| Message ID | 1308227453-2034-1-git-send-email-shawn.guo@linaro.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Jun 16, 2011 at 08:30:53PM +0800, Shawn Guo wrote: > Here is the user story that tells the need of the new api. The > mxs-mmc is the mmc host controller for Freescale MXS architecture. > There are a pair of mmc host specific parameters max_seg_size and > max_segs that mxs-mmc host driver needs to tell mmc core, so that > mmc core can know how big each data segment could be and how many > segments could be handled one time in a scatter list by host driver. > > The mxs-mmc driver is one user of dmaengine mxs-dma, and it will call > mxs-dma to transfer data in scatter list. That is to say mxs-mmc has > no idea of what max_seg_size and max_segs should be, because they are > all mxs-dma capability parameters, and mxs-mmc needs to query them > from mxs-dma. This approach would make sense if mxs-mmc were generic, but it's tied to mxs-dma, so it can just as well call mxs-dma to find out how many segments it supports. > Right now, there is well defined dma api (dma_get_max_seg_size) for > mmc to query max_seg_size from dma driver, but the one for max_segs > is missing. That's why mxs-mmc driver has to hard-code it. > > The mxs-mmc is just one example to demonstrate the need of the new > api, and there are other mmc host drivers (mxcmmc on imx-dma is > another example) and possibly even other dmaengine users need this > new api to know the maximum segments that dma driver can handle per > dma call. Again, mxcmmc can just call imx-dma directly.
On 17 June 2011 14:40, Matthew Wilcox <matthew@wil.cx> wrote: > On Thu, Jun 16, 2011 at 08:30:53PM +0800, Shawn Guo wrote: >> Here is the user story that tells the need of the new api. The >> mxs-mmc is the mmc host controller for Freescale MXS architecture. >> There are a pair of mmc host specific parameters max_seg_size and >> max_segs that mxs-mmc host driver needs to tell mmc core, so that >> mmc core can know how big each data segment could be and how many >> segments could be handled one time in a scatter list by host driver. >> >> The mxs-mmc driver is one user of dmaengine mxs-dma, and it will call >> mxs-dma to transfer data in scatter list. That is to say mxs-mmc has >> no idea of what max_seg_size and max_segs should be, because they are >> all mxs-dma capability parameters, and mxs-mmc needs to query them >> from mxs-dma. > > This approach would make sense if mxs-mmc were generic, but it's tied to > mxs-dma, so it can just as well call mxs-dma to find out how many segments > it supports. > mxs-dma use the generic dmaengine.h. The patch is not only intended for mxs-mmc. MMCI and other mmc host drivers need a way to query max_seg_number. It would be possible to store this number within drivers/dmaengine but this would not work for omap_hsmmc that doesn't use drivers/dmaengine Regards, Per
On Fri, 17 Jun 2011 06:40:35 -0600 Matthew Wilcox <matthew@wil.cx> wrote: > On Thu, Jun 16, 2011 at 08:30:53PM +0800, Shawn Guo wrote: > > Here is the user story that tells the need of the new api. The > > mxs-mmc is the mmc host controller for Freescale MXS architecture. > > There are a pair of mmc host specific parameters max_seg_size and > > max_segs that mxs-mmc host driver needs to tell mmc core, so that > > mmc core can know how big each data segment could be and how many > > segments could be handled one time in a scatter list by host driver. > > > > The mxs-mmc driver is one user of dmaengine mxs-dma, and it will call > > mxs-dma to transfer data in scatter list. That is to say mxs-mmc has > > no idea of what max_seg_size and max_segs should be, because they are > > all mxs-dma capability parameters, and mxs-mmc needs to query them > > from mxs-dma. > > This approach would make sense if mxs-mmc were generic, but it's tied to > mxs-dma, so it can just as well call mxs-dma to find out how many segments > it supports. SCSI HBA drivers stores the max number of sg entries in host->sg_tablesize (and scsi-ml tells the block layer about the limit)? So if we have the generic API to handle the value, scsi HBA drivers (and scsi-ml) could use it too?
diff --git a/include/linux/device.h b/include/linux/device.h index c66111a..f1152c5 100644 --- a/include/linux/device.h +++ b/include/linux/device.h @@ -481,12 +481,20 @@ extern int devres_release_group(struct device *dev, void *id); extern void *devm_kzalloc(struct device *dev, size_t size, gfp_t gfp); extern void devm_kfree(struct device *dev, void *p); +/* + * device_dma_parameters is a property of DMA provider, and it belongs to the + * 'struct device' that actually provides DMA service, typically the drivers + * under drivers/dma, although in some cases the DMA provider and block device + * uses DMA service happen to be the same 'struct device'. + * + * It's not necessary for every single DMA providers to have this structure, + * because some DMA providers simply do not have these parameters/limitations. + * For those do have, the DMA providers should be responsible for setting the + * parameters up. + */ struct device_dma_parameters { - /* - * a low level driver may set these to teach IOMMU code about - * sg limitations. - */ unsigned int max_segment_size; + unsigned int max_segment_number; unsigned long segment_boundary_mask; }; diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h index ba8319a..fd314f4 100644 --- a/include/linux/dma-mapping.h +++ b/include/linux/dma-mapping.h @@ -131,6 +131,21 @@ static inline unsigned int dma_set_max_seg_size(struct device *dev, return -EIO; } +static inline unsigned int dma_get_max_seg_number(struct device *dev) +{ + return dev->dma_parms ? dev->dma_parms->max_segment_number : 1; +} + +static inline unsigned int dma_set_max_seg_number(struct device *dev, + unsigned int number) +{ + if (dev->dma_parms) { + dev->dma_parms->max_segment_number = number; + return 0; + } else + return -EIO; +} + static inline unsigned long dma_get_seg_boundary(struct device *dev) { return dev->dma_parms ?
Like dma_set(get)_max_seg_size for max_segment_size, the patch adds max_segment_number into device_dma_parameters and creates the corresponding API dma_set(get)_max_seg_number for it. Here is the user story that tells the need of the new api. The mxs-mmc is the mmc host controller for Freescale MXS architecture. There are a pair of mmc host specific parameters max_seg_size and max_segs that mxs-mmc host driver needs to tell mmc core, so that mmc core can know how big each data segment could be and how many segments could be handled one time in a scatter list by host driver. The mxs-mmc driver is one user of dmaengine mxs-dma, and it will call mxs-dma to transfer data in scatter list. That is to say mxs-mmc has no idea of what max_seg_size and max_segs should be, because they are all mxs-dma capability parameters, and mxs-mmc needs to query them from mxs-dma. Right now, there is well defined dma api (dma_get_max_seg_size) for mmc to query max_seg_size from dma driver, but the one for max_segs is missing. That's why mxs-mmc driver has to hard-code it. The mxs-mmc is just one example to demonstrate the need of the new api, and there are other mmc host drivers (mxcmmc on imx-dma is another example) and possibly even other dmaengine users need this new api to know the maximum segments that dma driver can handle per dma call. Signed-off-by: Shawn Guo <shawn.guo@linaro.org> --- Reasons for resend: * Cc linux-scsi for comment, per request from FUJITA Tomonori * Take suggestion from Per Forlin to change patch subject to dma-mapping include/linux/device.h | 16 ++++++++++++---- include/linux/dma-mapping.h | 15 +++++++++++++++ 2 files changed, 27 insertions(+), 4 deletions(-)