Re: [PATCH v1 1/2] drm/bridge/synopsys: dsi: Fix dsi_host_transfer() return value

Philippe CORNU
2018-01-24T13:34:17Z

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
>>
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