Re: [PATCH] drm/dbi: Fix SPI Type 1 (9-bit) transfer

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi Noralf,

Le dim. 5 juil. 2020 à 17:58, Noralf Trønnes <noralf@xxxxxxxxxxx> a écrit :


Den 03.07.2020 16.13, skrev Paul Cercueil:
The function mipi_dbi_spi1_transfer() will transfer its payload as 9-bit data, the 9th (MSB) bit being the data/command bit. In order to do that, it unpacks the 8-bit values into 16-bit values, then sets the 9th bit if
 the byte corresponds to data, clears it otherwise. The 7 MSB are
padding. The array of now 16-bit values is then passed to the SPI core
 for transfer.

This function was broken since its introduction, as the length of the SPI transfer was set to the payload size before its conversion, but the
 payload doubled in size due to the 8-bit -> 16-bit conversion.

 Fixes: 02dd95fe3169 ("drm/tinydrm: Add MIPI DBI support")
 Cc: <stable@xxxxxxxxxxxxxxx> # 4.10

The code was moved to drm_mipi_dbi.c in 5.4 so this patch won't apply
before that.

I believe I can submit a patch for pre-5.4 too.

 Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
 ---

Thanks for fixing this, clearly I didn't test this. Probably because the
aux spi ip block on the Raspberry Pi that can do 9 bit didn't have a
driver at the time. Did you actually test this or was it spotted reading
the code?

I did test it on hardware, yes - that's how I spotted the bug.

-Paul

Reviewed-by: Noralf Trønnes <noralf@xxxxxxxxxxx>

  drivers/gpu/drm/drm_mipi_dbi.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_mipi_dbi.c b/drivers/gpu/drm/drm_mipi_dbi.c
 index bb27c82757f1..bf7888ad9ad4 100644
 --- a/drivers/gpu/drm/drm_mipi_dbi.c
 +++ b/drivers/gpu/drm/drm_mipi_dbi.c
@@ -923,7 +923,7 @@ static int mipi_dbi_spi1_transfer(struct mipi_dbi *dbi, int dc,
  			}
  		}

 -		tr.len = chunk;
 +		tr.len = chunk * 2;
  		len -= chunk;

  		ret = spi_sync(spi, &m);







[Index of Archives]     [Linux Kernel]     [Kernel Development Newbies]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite Hiking]     [Linux Kernel]     [Linux SCSI]

  Powered by Linux