| Message ID | 20110726075720.GL9653@n2100.arm.linux.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Tue, 2011-07-26 at 08:57 +0100, Russell King - ARM Linux wrote: > Here's an updated patch. > > 8<---------- > From: Russell King <rmk+kernel@arm.linux.org.uk> > DMAEngine: Improve slave/cyclic documentation > > Improve the documentation for the slave and cyclic DMA engine support > reformatting it for easier reading, adding further APIs, splitting it > into five steps, and including references to the documentation in > dmaengine.h. > > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> > --- > Documentation/dmaengine.txt | 211 ++++++++++++++++++++++++++++++------------- > 1 files changed, 146 insertions(+), 65 deletions(-) > > diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt > index 5a0cb1e..8c2e888 100644 > --- a/Documentation/dmaengine.txt > +++ b/Documentation/dmaengine.txt > @@ -10,87 +10,168 @@ > Below is a guide to device driver writers on how to use the Slave-DMA API of the > DMA Engine. This is applicable only for slave DMA usage only. > > -The slave DMA usage consists of following steps > +The slave DMA usage consists of following steps: > 1. Allocate a DMA slave channel > 2. Set slave and controller specific parameters > 3. Get a descriptor for transaction > 4. Submit the transaction and wait for callback notification > +5. Issue pending requests Thanks Russell, Applied with change to 4 above. Moved "and wait for callback notification" to 5. > > 1. Allocate a DMA slave channel > -Channel allocation is slightly different in the slave DMA context, client > -drivers typically need a channel from a particular DMA controller only and even > -in some cases a specific channel is desired. To request a channel > -dma_request_channel() API is used. > - > -Interface: > -struct dma_chan *dma_request_channel(dma_cap_mask_t mask, > - dma_filter_fn filter_fn, > - void *filter_param); > -where dma_filter_fn is defined as: > -typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param); > - > -When the optional 'filter_fn' parameter is set to NULL dma_request_channel > -simply returns the first channel that satisfies the capability mask. Otherwise, > -when the mask parameter is insufficient for specifying the necessary channel, > -the filter_fn routine can be used to disposition the available channels in the > -system. The filter_fn routine is called once for each free channel in the > -system. Upon seeing a suitable channel filter_fn returns DMA_ACK which flags > -that channel to be the return value from dma_request_channel. A channel > -allocated via this interface is exclusive to the caller, until > -dma_release_channel() is called. > + > + Channel allocation is slightly different in the slave DMA context, > + client drivers typically need a channel from a particular DMA > + controller only and even in some cases a specific channel is desired. > + To request a channel dma_request_channel() API is used. > + > + Interface: > + struct dma_chan *dma_request_channel(dma_cap_mask_t mask, > + dma_filter_fn filter_fn, > + void *filter_param); > + where dma_filter_fn is defined as: > + typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param); > + > + The 'filter_fn' parameter is optional, but highly recommended for > + slave and cyclic channels as they typically need to obtain a specific > + DMA channel. > + > + When the optional 'filter_fn' parameter is NULL, dma_request_channel() > + simply returns the first channel that satisfies the capability mask. > + > + Otherwise, the 'filter_fn' routine will be called once for each free > + channel which has a capability in 'mask'. 'filter_fn' is expected to > + return 'true' when the desired DMA channel is found. > + > + A channel allocated via this interface is exclusive to the caller, > + until dma_release_channel() is called. > > 2. Set slave and controller specific parameters > -Next step is always to pass some specific information to the DMA driver. Most of > -the generic information which a slave DMA can use is in struct dma_slave_config. > -It allows the clients to specify DMA direction, DMA addresses, bus widths, DMA > -burst lengths etc. If some DMA controllers have more parameters to be sent then > -they should try to embed struct dma_slave_config in their controller specific > -structure. That gives flexibility to client to pass more parameters, if > -required. > - > -Interface: > -int dmaengine_slave_config(struct dma_chan *chan, > - struct dma_slave_config *config) > + > + Next step is always to pass some specific information to the DMA > + driver. Most of the generic information which a slave DMA can use > + is in struct dma_slave_config. This allows the clients to specify > + DMA direction, DMA addresses, bus widths, DMA burst lengths etc > + for the peripheral. > + > + If some DMA controllers have more parameters to be sent then they > + should try to embed struct dma_slave_config in their controller > + specific structure. That gives flexibility to client to pass more > + parameters, if required. > + > + Interface: > + int dmaengine_slave_config(struct dma_chan *chan, > + struct dma_slave_config *config) > + > + Please see the dma_slave_config structure definition in dmaengine.h > + for a detailed explaination of the struct members. Please note > + that the 'direction' member will be going away as it duplicates the > + direction given in the prepare call. > > 3. Get a descriptor for transaction > -For slave usage the various modes of slave transfers supported by the > -DMA-engine are: > -slave_sg - DMA a list of scatter gather buffers from/to a peripheral > -dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the > + > + For slave usage the various modes of slave transfers supported by the > + DMA-engine are: > + > + slave_sg - DMA a list of scatter gather buffers from/to a peripheral > + dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the > operation is explicitly stopped. > -The non NULL return of this transfer API represents a "descriptor" for the given > -transaction. > > -Interface: > -struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_sg)( > + A non-NULL return of this transfer API represents a "descriptor" for > + the given transaction. > + > + Interface: > + struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_sg)( > struct dma_chan *chan, > struct scatterlist *dst_sg, unsigned int dst_nents, > struct scatterlist *src_sg, unsigned int src_nents, > unsigned long flags); > -struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)( > + > + struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)( > struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len, > size_t period_len, enum dma_data_direction direction); > > -4. Submit the transaction and wait for callback notification > -To schedule the transaction to be scheduled by dma device, the "descriptor" > -returned in above (3) needs to be submitted. > -To tell the dma driver that a transaction is ready to be serviced, the > -descriptor->submit() callback needs to be invoked. This chains the descriptor to > -the pending queue. > -The transactions in the pending queue can be activated by calling the > -issue_pending API. If channel is idle then the first transaction in queue is > -started and subsequent ones queued up. > -On completion of the DMA operation the next in queue is submitted and a tasklet > -triggered. The tasklet would then call the client driver completion callback > -routine for notification, if set. > -Interface: > -void dma_async_issue_pending(struct dma_chan *chan); > - > -============================================================================== > - > -Additional usage notes for dma driver writers > -1/ Although DMA engine specifies that completion callback routines cannot submit > -any new operations, but typically for slave DMA subsequent transaction may not > -be available for submit prior to callback routine being called. This requirement > -is not a requirement for DMA-slave devices. But they should take care to drop > -the spin-lock they might be holding before calling the callback routine > + Once a descriptor has been obtained, the callback information can be > + added and must then be submitted. Some DMA engine drivers may hold a > + spinlock between a successful preparation and submission so it is > + important that these two operations are closely paired. > + > + Note: > + Although the async_tx API specifies that completion callback > + routines cannot submit any new operations, this is not the > + case for slave/cyclic DMA. > + > + For slave DMA, the subsequent transaction may not be available > + for submission prior to callback function being invoked, so > + slave DMA callbacks are permitted to prepare and submit a new > + transaction. > + > + For cyclic DMA, a callback function may wish to terminate the > + DMA via dmaengine_terminate_all(). > + > + Therefore, it is important that DMA engine drivers drop any > + locks before calling the callback function which may cause a > + deadlock. > + > + Note that callbacks will always be invoked from the DMA > + engines tasklet, never from interrupt context. > + > +4. Submit the transaction > + > + Once the descriptor has been prepared and the callback information > + added, it must be placed on the DMA engine drivers pending queue. > + > + Interface: > + dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc) > + > + This returns a cookie can be used to check the progress of DMA engine > + activity via other DMA engine calls not covered in this document. > + > + dmaengine_submit() will not start the DMA operation, it merely adds > + it to the pending queue. For this, see step 5, dma_async_issue_pending. > + > +5. Issue pending DMA requests and wait for callback notification > + > + The transactions in the pending queue can be activated by calling the > + issue_pending API. If channel is idle then the first transaction in > + queue is started and subsequent ones queued up. > + > + On completion of each DMA operation, the next in queue is started and > + a tasklet triggered. The tasklet will then call the client driver > + completion callback routine for notification, if set. > + > + Interface: > + void dma_async_issue_pending(struct dma_chan *chan); > + > +Further APIs: > + > +1. int dmaengine_terminate_all(struct dma_chan *chan) > + > + This causes all activity for the DMA channel to be stopped, and may > + discard data in the DMA FIFO which hasn't been fully transferred. > + No callback functions will be called for any incomplete transfers. > + > +2. int dmaengine_pause(struct dma_chan *chan) > + > + This pauses activity on the DMA channel without data loss. > + > +3. int dmaengine_resume(struct dma_chan *chan) > + > + Resume a previously paused DMA channel. It is invalid to resume a > + channel which is not currently paused. > + > +4. enum dma_status dma_async_is_tx_complete(struct dma_chan *chan, > + dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used) > + > + This can be used to check the status of the channel. Please see > + the documentation in include/linux/dmaengine.h for a more complete > + description of this API. > + > + This can be used in conjunction with dma_async_is_complete() and > + the cookie returned from 'descriptor->submit()' to check for > + completion of a specific DMA transaction. > + > + Note: > + Not all DMA engine drivers can return reliable information for > + a running DMA channel. It is recommended that DMA engine users > + pause or stop (via dmaengine_terminate_all) the channel before > + using this API. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Tue, Jul 26, 2011 at 3:05 PM, Vinod Koul <vkoul@infradead.org> wrote: > On Tue, 2011-07-26 at 08:57 +0100, Russell King - ARM Linux wrote: >> Here's an updated patch. >> >> 8<---------- >> From: Russell King <rmk+kernel@arm.linux.org.uk> >> DMAEngine: Improve slave/cyclic documentation >> >> Improve the documentation for the slave and cyclic DMA engine support >> reformatting it for easier reading, adding further APIs, splitting it >> into five steps, and including references to the documentation in >> dmaengine.h. >> >> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> >> --- >> Documentation/dmaengine.txt | 211 ++++++++++++++++++++++++++++++------------- >> 1 files changed, 146 insertions(+), 65 deletions(-) >> >> diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt >> index 5a0cb1e..8c2e888 100644 >> --- a/Documentation/dmaengine.txt >> +++ b/Documentation/dmaengine.txt >> @@ -10,87 +10,168 @@ >> Below is a guide to device driver writers on how to use the Slave-DMA API of the >> DMA Engine. This is applicable only for slave DMA usage only. >> >> -The slave DMA usage consists of following steps >> +The slave DMA usage consists of following steps: >> 1. Allocate a DMA slave channel >> 2. Set slave and controller specific parameters >> 3. Get a descriptor for transaction >> 4. Submit the transaction and wait for callback notification >> +5. Issue pending requests > Thanks Russell, > > Applied with change to 4 above. Moved "and wait for callback > notification" to 5. > Dear Vinod, Since it came from the RMK, most probably it'll be the best. But applying patches upon personal timeout seems very dangerous. People not responding doesn't mean only either people agree completely or they don't care. Some might be interested but too busy with current tasks that they need time to check... please make some policy for such cases. It already happened with the patch from Rob, which you probably have to revert. IMHO, if nobody replied, maybe you could first ack the patch and wait for, say a week, before applying? That way people will know they have to hurry if they care otherwise the patch is going upstream as such. Thanks -Jassi
On Tue, Jul 26, 2011 at 08:07:44PM +0530, Jassi Brar wrote: > Dear Vinod, > > Since it came from the RMK, most probably it'll be the best. > > But applying patches upon personal timeout seems very dangerous. Ehh what? Is there any contention over this documentation patch? It's not adding anything new, it's just documenting the facts as they stand today about the API and its use. > People not responding doesn't mean only either people agree completely > or they don't care. Some might be interested but too busy with current tasks > that they need time to check... please make some policy for such cases. > > It already happened with the patch from Rob, which you probably have to > revert. > > IMHO, if nobody replied, maybe you could first ack the patch and wait > for, say a week, before applying? > That way people will know they have to hurry if they care otherwise > the patch is going upstream as such. A week is far too long. That's how patches get lost and missed.
On Tue, Jul 26, 2011 at 10:50 PM, Russell King - ARM Linux <linux@arm.linux.org.uk> wrote: > On Tue, Jul 26, 2011 at 08:07:44PM +0530, Jassi Brar wrote: >> Dear Vinod, >> >> Since it came from the RMK, most probably it'll be the best. >> >> But applying patches upon personal timeout seems very dangerous. > > Ehh what? Is there any contention over this documentation patch? I haven't yet read it... even after reading I would object only if I found your patch disturbing enough to disrupt my bowel movements. Which I don't think would be the case. I just observed it is second time that Vinod applied a patch without any ack or prior alert. > >> People not responding doesn't mean only either people agree completely >> or they don't care. Some might be interested but too busy with current tasks >> that they need time to check... please make some policy for such cases. >> >> It already happened with the patch from Rob, which you probably have to >> revert. >> >> IMHO, if nobody replied, maybe you could first ack the patch and wait >> for, say a week, before applying? >> That way people will know they have to hurry if they care otherwise >> the patch is going upstream as such. > > A week is far too long. That's how patches get lost and missed. > He may decide to wait shorter, but imho a week after the first ack isn't that long.
On Tue, Jul 26, 2011 at 11:55 AM, Jassi Brar <jassisinghbrar@gmail.com> wrote: > On Tue, Jul 26, 2011 at 10:50 PM, Russell King - ARM Linux > <linux@arm.linux.org.uk> wrote: >> On Tue, Jul 26, 2011 at 08:07:44PM +0530, Jassi Brar wrote: >>> Dear Vinod, >>> >>> Since it came from the RMK, most probably it'll be the best. >>> >>> But applying patches upon personal timeout seems very dangerous. >> >> Ehh what? Is there any contention over this documentation patch? > I haven't yet read it... even after reading I would object only if I found > your patch disturbing enough to disrupt my bowel movements. Which > I don't think would be the case. > > I just observed it is second time that Vinod applied a patch without any > ack or prior alert. Applying patches without waiting for other Acks is absolutely a reasonable thing for a maintainer to do. The job of maintainership is to apply good judgement on when patches can immediately be applied (and therefore no longer consuming limited attention) and when patches need further acks. g.
On Tue, Jul 26, 2011 at 11:25:13PM +0530, Jassi Brar wrote: > On Tue, Jul 26, 2011 at 10:50 PM, Russell King - ARM Linux > <linux@arm.linux.org.uk> wrote: > > On Tue, Jul 26, 2011 at 08:07:44PM +0530, Jassi Brar wrote: > >> Dear Vinod, > >> > >> Since it came from the RMK, most probably it'll be the best. > >> > >> But applying patches upon personal timeout seems very dangerous. > > > > Ehh what? Is there any contention over this documentation patch? > I haven't yet read it... even after reading I would object only if I found > your patch disturbing enough to disrupt my bowel movements. Which > I don't think would be the case. > > I just observed it is second time that Vinod applied a patch without any > ack or prior alert. That's what happens - no one says "I'm going to apply this patch" before they apply it. They just apply it to their tree and move on. Vinod, being the nominated maintainer for the slave DMA engine support has the authority to do that for that area of code.
On Tue, 2011-07-26 at 23:25 +0530, Jassi Brar wrote: > On Tue, Jul 26, 2011 at 10:50 PM, Russell King - ARM Linux > <linux@arm.linux.org.uk> wrote: > > On Tue, Jul 26, 2011 at 08:07:44PM +0530, Jassi Brar wrote: > >> Dear Vinod, > >> > >> Since it came from the RMK, most probably it'll be the best. > >> > >> But applying patches upon personal timeout seems very dangerous. > > > > Ehh what? Is there any contention over this documentation patch? > I haven't yet read it... even after reading I would object only if I found > your patch disturbing enough to disrupt my bowel movements. Which > I don't think would be the case. Jassi, Since this was a doc patch, I applied it soon enough, doesn't sound dangerous to me ! If you have any updates you would like, pls feel free to send a patch. > > I just observed it is second time that Vinod applied a patch without any > ack or prior alert. And you can't ignore the fact that you had almost _two_ weeks to ack the patch from Rob, but.... You will get ample time to ack a patch, if you don't you can always point out and I will do the right thing, which in this case was to revert. > > > > >> People not responding doesn't mean only either people agree completely > >> or they don't care. Some might be interested but too busy with current tasks > >> that they need time to check... please make some policy for such cases. > >> > >> It already happened with the patch from Rob, which you probably have to > >> revert. > >> > >> IMHO, if nobody replied, maybe you could first ack the patch and wait > >> for, say a week, before applying? > >> That way people will know they have to hurry if they care otherwise > >> the patch is going upstream as such. > > > > A week is far too long. That's how patches get lost and missed. > > > He may decide to wait shorter, but imho a week after the first ack > isn't that long. > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
On Tue, Jul 26, 2011 at 03:05:33PM +0530, Vinod Koul wrote: > On Tue, 2011-07-26 at 08:57 +0100, Russell King - ARM Linux wrote: > > Here's an updated patch. > > > > 8<---------- > > From: Russell King <rmk+kernel@arm.linux.org.uk> > > DMAEngine: Improve slave/cyclic documentation > > > > Improve the documentation for the slave and cyclic DMA engine support > > reformatting it for easier reading, adding further APIs, splitting it > > into five steps, and including references to the documentation in > > dmaengine.h. > > > > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> > > --- > > Documentation/dmaengine.txt | 211 ++++++++++++++++++++++++++++++------------- > > 1 files changed, 146 insertions(+), 65 deletions(-) > > > > diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt > > index 5a0cb1e..8c2e888 100644 > > --- a/Documentation/dmaengine.txt > > +++ b/Documentation/dmaengine.txt > > @@ -10,87 +10,168 @@ > > Below is a guide to device driver writers on how to use the Slave-DMA API of the > > DMA Engine. This is applicable only for slave DMA usage only. > > > > -The slave DMA usage consists of following steps > > +The slave DMA usage consists of following steps: > > 1. Allocate a DMA slave channel > > 2. Set slave and controller specific parameters > > 3. Get a descriptor for transaction > > 4. Submit the transaction and wait for callback notification > > +5. Issue pending requests > Thanks Russell, > > Applied with change to 4 above. Moved "and wait for callback > notification" to 5. BTW, did you apply this one or the later one with the improved documentation for dma mapping and fixed interface for slave transfers etc. ?
On Wed, 2011-07-27 at 10:01 +0100, Russell King - ARM Linux wrote: > On Tue, Jul 26, 2011 at 03:05:33PM +0530, Vinod Koul wrote: > > On Tue, 2011-07-26 at 08:57 +0100, Russell King - ARM Linux wrote: > > > Here's an updated patch. > > > > > > 8<---------- > > > From: Russell King <rmk+kernel@arm.linux.org.uk> > > > DMAEngine: Improve slave/cyclic documentation > > > > > > Improve the documentation for the slave and cyclic DMA engine support > > > reformatting it for easier reading, adding further APIs, splitting it > > > into five steps, and including references to the documentation in > > > dmaengine.h. > > > > > > Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk> > > > --- > > > Documentation/dmaengine.txt | 211 ++++++++++++++++++++++++++++++------------- > > > 1 files changed, 146 insertions(+), 65 deletions(-) > > > > > > diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt > > > index 5a0cb1e..8c2e888 100644 > > > --- a/Documentation/dmaengine.txt > > > +++ b/Documentation/dmaengine.txt > > > @@ -10,87 +10,168 @@ > > > Below is a guide to device driver writers on how to use the Slave-DMA API of the > > > DMA Engine. This is applicable only for slave DMA usage only. > > > > > > -The slave DMA usage consists of following steps > > > +The slave DMA usage consists of following steps: > > > 1. Allocate a DMA slave channel > > > 2. Set slave and controller specific parameters > > > 3. Get a descriptor for transaction > > > 4. Submit the transaction and wait for callback notification > > > +5. Issue pending requests > > Thanks Russell, > > > > Applied with change to 4 above. Moved "and wait for callback > > notification" to 5. > > BTW, did you apply this one or the later one with the improved > documentation for dma mapping and fixed interface for slave > transfers etc. ? I changed it to second one, not pushed yet. I am rebasing the tree to 3.0. You should see updated version in tree later in the evening today
diff --git a/Documentation/dmaengine.txt b/Documentation/dmaengine.txt index 5a0cb1e..8c2e888 100644 --- a/Documentation/dmaengine.txt +++ b/Documentation/dmaengine.txt @@ -10,87 +10,168 @@ Below is a guide to device driver writers on how to use the Slave-DMA API of the DMA Engine. This is applicable only for slave DMA usage only. -The slave DMA usage consists of following steps +The slave DMA usage consists of following steps: 1. Allocate a DMA slave channel 2. Set slave and controller specific parameters 3. Get a descriptor for transaction 4. Submit the transaction and wait for callback notification +5. Issue pending requests 1. Allocate a DMA slave channel -Channel allocation is slightly different in the slave DMA context, client -drivers typically need a channel from a particular DMA controller only and even -in some cases a specific channel is desired. To request a channel -dma_request_channel() API is used. - -Interface: -struct dma_chan *dma_request_channel(dma_cap_mask_t mask, - dma_filter_fn filter_fn, - void *filter_param); -where dma_filter_fn is defined as: -typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param); - -When the optional 'filter_fn' parameter is set to NULL dma_request_channel -simply returns the first channel that satisfies the capability mask. Otherwise, -when the mask parameter is insufficient for specifying the necessary channel, -the filter_fn routine can be used to disposition the available channels in the -system. The filter_fn routine is called once for each free channel in the -system. Upon seeing a suitable channel filter_fn returns DMA_ACK which flags -that channel to be the return value from dma_request_channel. A channel -allocated via this interface is exclusive to the caller, until -dma_release_channel() is called. + + Channel allocation is slightly different in the slave DMA context, + client drivers typically need a channel from a particular DMA + controller only and even in some cases a specific channel is desired. + To request a channel dma_request_channel() API is used. + + Interface: + struct dma_chan *dma_request_channel(dma_cap_mask_t mask, + dma_filter_fn filter_fn, + void *filter_param); + where dma_filter_fn is defined as: + typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param); + + The 'filter_fn' parameter is optional, but highly recommended for + slave and cyclic channels as they typically need to obtain a specific + DMA channel. + + When the optional 'filter_fn' parameter is NULL, dma_request_channel() + simply returns the first channel that satisfies the capability mask. + + Otherwise, the 'filter_fn' routine will be called once for each free + channel which has a capability in 'mask'. 'filter_fn' is expected to + return 'true' when the desired DMA channel is found. + + A channel allocated via this interface is exclusive to the caller, + until dma_release_channel() is called. 2. Set slave and controller specific parameters -Next step is always to pass some specific information to the DMA driver. Most of -the generic information which a slave DMA can use is in struct dma_slave_config. -It allows the clients to specify DMA direction, DMA addresses, bus widths, DMA -burst lengths etc. If some DMA controllers have more parameters to be sent then -they should try to embed struct dma_slave_config in their controller specific -structure. That gives flexibility to client to pass more parameters, if -required. - -Interface: -int dmaengine_slave_config(struct dma_chan *chan, - struct dma_slave_config *config) + + Next step is always to pass some specific information to the DMA + driver. Most of the generic information which a slave DMA can use + is in struct dma_slave_config. This allows the clients to specify + DMA direction, DMA addresses, bus widths, DMA burst lengths etc + for the peripheral. + + If some DMA controllers have more parameters to be sent then they + should try to embed struct dma_slave_config in their controller + specific structure. That gives flexibility to client to pass more + parameters, if required. + + Interface: + int dmaengine_slave_config(struct dma_chan *chan, + struct dma_slave_config *config) + + Please see the dma_slave_config structure definition in dmaengine.h + for a detailed explaination of the struct members. Please note + that the 'direction' member will be going away as it duplicates the + direction given in the prepare call. 3. Get a descriptor for transaction -For slave usage the various modes of slave transfers supported by the -DMA-engine are: -slave_sg - DMA a list of scatter gather buffers from/to a peripheral -dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the + + For slave usage the various modes of slave transfers supported by the + DMA-engine are: + + slave_sg - DMA a list of scatter gather buffers from/to a peripheral + dma_cyclic - Perform a cyclic DMA operation from/to a peripheral till the operation is explicitly stopped. -The non NULL return of this transfer API represents a "descriptor" for the given -transaction. -Interface: -struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_sg)( + A non-NULL return of this transfer API represents a "descriptor" for + the given transaction. + + Interface: + struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_sg)( struct dma_chan *chan, struct scatterlist *dst_sg, unsigned int dst_nents, struct scatterlist *src_sg, unsigned int src_nents, unsigned long flags); -struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)( + + struct dma_async_tx_descriptor *(*chan->device->device_prep_dma_cyclic)( struct dma_chan *chan, dma_addr_t buf_addr, size_t buf_len, size_t period_len, enum dma_data_direction direction); -4. Submit the transaction and wait for callback notification -To schedule the transaction to be scheduled by dma device, the "descriptor" -returned in above (3) needs to be submitted. -To tell the dma driver that a transaction is ready to be serviced, the -descriptor->submit() callback needs to be invoked. This chains the descriptor to -the pending queue. -The transactions in the pending queue can be activated by calling the -issue_pending API. If channel is idle then the first transaction in queue is -started and subsequent ones queued up. -On completion of the DMA operation the next in queue is submitted and a tasklet -triggered. The tasklet would then call the client driver completion callback -routine for notification, if set. -Interface: -void dma_async_issue_pending(struct dma_chan *chan); - -============================================================================== - -Additional usage notes for dma driver writers -1/ Although DMA engine specifies that completion callback routines cannot submit -any new operations, but typically for slave DMA subsequent transaction may not -be available for submit prior to callback routine being called. This requirement -is not a requirement for DMA-slave devices. But they should take care to drop -the spin-lock they might be holding before calling the callback routine + Once a descriptor has been obtained, the callback information can be + added and must then be submitted. Some DMA engine drivers may hold a + spinlock between a successful preparation and submission so it is + important that these two operations are closely paired. + + Note: + Although the async_tx API specifies that completion callback + routines cannot submit any new operations, this is not the + case for slave/cyclic DMA. + + For slave DMA, the subsequent transaction may not be available + for submission prior to callback function being invoked, so + slave DMA callbacks are permitted to prepare and submit a new + transaction. + + For cyclic DMA, a callback function may wish to terminate the + DMA via dmaengine_terminate_all(). + + Therefore, it is important that DMA engine drivers drop any + locks before calling the callback function which may cause a + deadlock. + + Note that callbacks will always be invoked from the DMA + engines tasklet, never from interrupt context. + +4. Submit the transaction + + Once the descriptor has been prepared and the callback information + added, it must be placed on the DMA engine drivers pending queue. + + Interface: + dma_cookie_t dmaengine_submit(struct dma_async_tx_descriptor *desc) + + This returns a cookie can be used to check the progress of DMA engine + activity via other DMA engine calls not covered in this document. + + dmaengine_submit() will not start the DMA operation, it merely adds + it to the pending queue. For this, see step 5, dma_async_issue_pending. + +5. Issue pending DMA requests and wait for callback notification + + The transactions in the pending queue can be activated by calling the + issue_pending API. If channel is idle then the first transaction in + queue is started and subsequent ones queued up. + + On completion of each DMA operation, the next in queue is started and + a tasklet triggered. The tasklet will then call the client driver + completion callback routine for notification, if set. + + Interface: + void dma_async_issue_pending(struct dma_chan *chan); + +Further APIs: + +1. int dmaengine_terminate_all(struct dma_chan *chan) + + This causes all activity for the DMA channel to be stopped, and may + discard data in the DMA FIFO which hasn't been fully transferred. + No callback functions will be called for any incomplete transfers. + +2. int dmaengine_pause(struct dma_chan *chan) + + This pauses activity on the DMA channel without data loss. + +3. int dmaengine_resume(struct dma_chan *chan) + + Resume a previously paused DMA channel. It is invalid to resume a + channel which is not currently paused. + +4. enum dma_status dma_async_is_tx_complete(struct dma_chan *chan, + dma_cookie_t cookie, dma_cookie_t *last, dma_cookie_t *used) + + This can be used to check the status of the channel. Please see + the documentation in include/linux/dmaengine.h for a more complete + description of this API. + + This can be used in conjunction with dma_async_is_complete() and + the cookie returned from 'descriptor->submit()' to check for + completion of a specific DMA transaction. + + Note: + Not all DMA engine drivers can return reliable information for + a running DMA channel. It is recommended that DMA engine users + pause or stop (via dmaengine_terminate_all) the channel before + using this API.