| Message ID | 20180123142618.28384-2-philippe.cornu@st.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Philippe, On Tue, Jan 23, 2018 at 6:26 AM, Philippe Cornu <philippe.cornu@st.com> wrote: > The dw_mipi_dsi_host_transfer() must return the number of > bytes transmitted/received on success instead of 0. I'm a little confused. As of the latest drm-misc-next I'm looking at, this still has conflicting documentation. For ->transfer(): On success it shall return the number of bytes * transmitted for write packets or the number of bytes received for read * packets. While mipi_dsi_generic_read() says: * Return: The number of bytes successfully read or a negative error code on * failure. But it just returns the value that ->transfer() returns. So I'm not sure whether the documentation is still wrong, or if the implementation is. Anyway, I guess maybe that isn't super-critical to *this* patch, since we don't have RX support yet... > Note: nb_bytes is introduced in this patch as it will be > re-used with the future dcs/generic dsi read feature. It feels like you could just wait to add that when you need it? It really feels trivial and useless right now :) Brian > > Signed-off-by: Philippe Cornu <philippe.cornu@st.com> > --- > drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c > index f458798af788..096cf5e5bb30 100644 > --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c > +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c > @@ -403,7 +403,7 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host, > { > struct dw_mipi_dsi *dsi = host_to_dsi(host); > struct mipi_dsi_packet packet; > - int ret; > + int ret, nb_bytes; > > ret = mipi_dsi_create_packet(&packet, msg); > if (ret) { > @@ -413,7 +413,13 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host, > > dw_mipi_message_config(dsi, msg); > > - return dw_mipi_dsi_write(dsi, &packet); > + ret = dw_mipi_dsi_write(dsi, &packet); > + if (ret) > + return ret; > + > + nb_bytes = packet.size; > + > + return nb_bytes; > } > > static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = { > -- > 2.15.1 >
Hi Brian, And many thanks for your review. On 01/23/2018 10:38 PM, Brian Norris wrote: > Hi Philippe, > > On Tue, Jan 23, 2018 at 6:26 AM, Philippe Cornu <philippe.cornu@st.com> wrote: >> The dw_mipi_dsi_host_transfer() must return the number of >> bytes transmitted/received on success instead of 0. > > I'm a little confused. As of the latest drm-misc-next I'm looking at, > this still has conflicting documentation. > > For ->transfer(): > > On success it shall return the number of bytes > * transmitted for write packets or the number of bytes received for read > * packets. > > While mipi_dsi_generic_read() says: > > * Return: The number of bytes successfully read or a negative error code on > * failure. > > But it just returns the value that ->transfer() returns. > Not sure to follow you here: mipi_dsi_generic_read() will trig a dsi generic read so it has to return "the number of bytes received for read packets" as explained for the ->transfer() function... so it looks "coherent"... But maybe you want to point out something different? > So I'm not sure whether the documentation is still wrong, or if the > implementation is. > > Anyway, I guess maybe that isn't super-critical to *this* patch, since > we don't have RX support yet... > The main reason why I want to "fix" this is because I do not want to explain to our customers (writing dsi panel drivers) why we have a different returned value compare to other platforms : ) >> Note: nb_bytes is introduced in this patch as it will be >> re-used with the future dcs/generic dsi read feature. > > It feels like you could just wait to add that when you need it? It > really feels trivial and useless right now :) > > Brian > Thanks, I agree, I will write & send a simpler version. Philippe :-) >> >> Signed-off-by: Philippe Cornu <philippe.cornu@st.com> >> --- >> drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 10 ++++++++-- >> 1 file changed, 8 insertions(+), 2 deletions(-) >> >> diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c >> index f458798af788..096cf5e5bb30 100644 >> --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c >> +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c >> @@ -403,7 +403,7 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host, >> { >> struct dw_mipi_dsi *dsi = host_to_dsi(host); >> struct mipi_dsi_packet packet; >> - int ret; >> + int ret, nb_bytes; >> >> ret = mipi_dsi_create_packet(&packet, msg); >> if (ret) { >> @@ -413,7 +413,13 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host, >> >> dw_mipi_message_config(dsi, msg); >> >> - return dw_mipi_dsi_write(dsi, &packet); >> + ret = dw_mipi_dsi_write(dsi, &packet); >> + if (ret) >> + return ret; >> + >> + nb_bytes = packet.size; >> + >> + return nb_bytes; >> } >> >> static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = { >> -- >> 2.15.1 >> > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel >
Hi Philippe, On Wed, Jan 24, 2018 at 01:33:54PM +0000, Philippe CORNU wrote: > On 01/23/2018 10:38 PM, Brian Norris wrote: > > Hi Philippe, > > > > On Tue, Jan 23, 2018 at 6:26 AM, Philippe Cornu <philippe.cornu@st.com> wrote: > >> The dw_mipi_dsi_host_transfer() must return the number of > >> bytes transmitted/received on success instead of 0. > > > > I'm a little confused. As of the latest drm-misc-next I'm looking at, > > this still has conflicting documentation. > > > > For ->transfer(): > > > > On success it shall return the number of bytes > > * transmitted for write packets or the number of bytes received for read > > * packets. > > > > While mipi_dsi_generic_read() says: > > > > * Return: The number of bytes successfully read or a negative error code on > > * failure. > > > > But it just returns the value that ->transfer() returns. > > > > Not sure to follow you here: mipi_dsi_generic_read() will trig a dsi > generic read so it has to return "the number of bytes received for read > packets" as explained for the ->transfer() function... so it looks > "coherent"... > > But maybe you want to point out something different? Actually, reading back what I wrote, I'm not sure it made sense. I think *I* was confusing "supporting TX only" with "supporting TX and RX". I believe the documentation isn't conflicting, but your current patch is a little misleading. With your current patch, you're returning the 'mipi_dsi_packet::size', which is the sum of both TX and RX. Since we only support TX right now, I suppose that actually is fine (because 'rx_len == 0'). But if we start supporting RX too, then this field is not the right one to return. Anyway, maybe this patch was fine as it was. But when you get RX support, this will have to be something like: if (msg->rx_len) return msg->rx_len; else return packet.size; BTW, does anyone actually care about seeing the number of TX bytes returned? That seems weird, because I wouldn't expect you'd get a good result from a partial TX (dunno about partial RX). And I also see that there are other drivers that get this all wrong too. See mtk_dsi_host_transfer(), which only returns 0 for TX and 'recv_cnt' for RX. So all-in-all, maybe my problem isn't that the documentation is conflicting, exactly, but that the requirements are somewhat odd, such that either implementations get it wrong (2 of 3 that I've looked at!), or they have to write somewhat odd special-casing. > > So I'm not sure whether the documentation is still wrong, or if the > > implementation is. > > > > Anyway, I guess maybe that isn't super-critical to *this* patch, since > > we don't have RX support yet... > > > > The main reason why I want to "fix" this is because I do not want to > explain to our customers (writing dsi panel drivers) why we have a > different returned value compare to other platforms : ) Brian
On 24.01.2018 19:37, Brian Norris wrote: > Hi Philippe, > > On Wed, Jan 24, 2018 at 01:33:54PM +0000, Philippe CORNU wrote: >> On 01/23/2018 10:38 PM, Brian Norris wrote: >>> Hi Philippe, >>> >>> On Tue, Jan 23, 2018 at 6:26 AM, Philippe Cornu <philippe.cornu@st.com> wrote: >>>> The dw_mipi_dsi_host_transfer() must return the number of >>>> bytes transmitted/received on success instead of 0. >>> I'm a little confused. As of the latest drm-misc-next I'm looking at, >>> this still has conflicting documentation. >>> >>> For ->transfer(): >>> >>> On success it shall return the number of bytes >>> * transmitted for write packets or the number of bytes received for read >>> * packets. >>> >>> While mipi_dsi_generic_read() says: >>> >>> * Return: The number of bytes successfully read or a negative error code on >>> * failure. >>> >>> But it just returns the value that ->transfer() returns. >>> >> Not sure to follow you here: mipi_dsi_generic_read() will trig a dsi >> generic read so it has to return "the number of bytes received for read >> packets" as explained for the ->transfer() function... so it looks >> "coherent"... >> >> But maybe you want to point out something different? > Actually, reading back what I wrote, I'm not sure it made sense. I think > *I* was confusing "supporting TX only" with "supporting TX and RX". I > believe the documentation isn't conflicting, but your current patch is a > little misleading. > > With your current patch, you're returning the 'mipi_dsi_packet::size', > which is the sum of both TX and RX. I did not found docs saying mipi_dsi_packet::size is a sum of tx and rx. tx and rx packets are two different packets, so they do not sum up. But thanks for bringing it up, it shows docs are incomplete/misleading. > Since we only support TX right now, > I suppose that actually is fine (because 'rx_len == 0'). But if we start > supporting RX too, then this field is not the right one to return. > > Anyway, maybe this patch was fine as it was. But when you get RX > support, this will have to be something like: > > if (msg->rx_len) > return msg->rx_len; > else > return packet.size; > > BTW, does anyone actually care about seeing the number of TX bytes > returned? That seems weird, because I wouldn't expect you'd get a good > result from a partial TX (dunno about partial RX). And I also see that > there are other drivers that get this all wrong too. See > mtk_dsi_host_transfer(), which only returns 0 for TX and 'recv_cnt' for > RX. As far as I remember MIPI DSI standard does not allow partial TX, it is all-or-nothing operation. > > So all-in-all, maybe my problem isn't that the documentation is > conflicting, exactly, but that the requirements are somewhat odd, such > that either implementations get it wrong (2 of 3 that I've looked at!), > or they have to write somewhat odd special-casing. mipi_dsi_host_ops::transfer in case of write sends only tx packet, in case of read it sends tx packets and receives rx packet, so it can be confusing what it should return in case of read. IMO changing mipi_dsi_host_ops::transfer to always return number of bytes RECEIVED or error should make it clearer and simpler. +CC Thierry Regards Andrzej > >>> So I'm not sure whether the documentation is still wrong, or if the >>> implementation is. >>> >>> Anyway, I guess maybe that isn't super-critical to *this* patch, since >>> we don't have RX support yet... >>> >> The main reason why I want to "fix" this is because I do not want to >> explain to our customers (writing dsi panel drivers) why we have a >> different returned value compare to other platforms : ) > Brian > _______________________________________________ > dri-devel mailing list > dri-devel@lists.freedesktop.org > https://lists.freedesktop.org/mailman/listinfo/dri-devel
On Thu, Jan 25, 2018 at 4:16 AM, Andrzej Hajda <a.hajda@samsung.com> wrote: > On 24.01.2018 19:37, Brian Norris wrote: >> With your current patch, you're returning the 'mipi_dsi_packet::size', >> which is the sum of both TX and RX. > > I did not found docs saying mipi_dsi_packet::size is a sum of tx and rx. > tx and rx packets are two different packets, so they do not sum up. > But thanks for bringing it up, it shows docs are incomplete/misleading. Ugh, I misread that again. No, mipi_dsi_packet::size is NOT claimed to contain both TX and RX. It just says "size of the packet", and packet clearly does not hold the RX data anyway. I don't know what's happening to my reading comprehension... But the mismatch on whether drivers implement these correctly and whether any callers actually care about the documented semantics still stands. Brian
diff --git a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c index f458798af788..096cf5e5bb30 100644 --- a/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c +++ b/drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c @@ -403,7 +403,7 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host, { struct dw_mipi_dsi *dsi = host_to_dsi(host); struct mipi_dsi_packet packet; - int ret; + int ret, nb_bytes; ret = mipi_dsi_create_packet(&packet, msg); if (ret) { @@ -413,7 +413,13 @@ static ssize_t dw_mipi_dsi_host_transfer(struct mipi_dsi_host *host, dw_mipi_message_config(dsi, msg); - return dw_mipi_dsi_write(dsi, &packet); + ret = dw_mipi_dsi_write(dsi, &packet); + if (ret) + return ret; + + nb_bytes = packet.size; + + return nb_bytes; } static const struct mipi_dsi_host_ops dw_mipi_dsi_host_ops = {
The dw_mipi_dsi_host_transfer() must return the number of bytes transmitted/received on success instead of 0. Note: nb_bytes is introduced in this patch as it will be re-used with the future dcs/generic dsi read feature. Signed-off-by: Philippe Cornu <philippe.cornu@st.com> --- drivers/gpu/drm/bridge/synopsys/dw-mipi-dsi.c | 10 ++++++++-- 1 file changed, 8 insertions(+), 2 deletions(-)