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

[Sam Ravnborg]

Hi Paul.

On Fri, Jul 03, 2020 at 04:23:57PM +0200, Sam Ravnborg wrote:
> On Fri, Jul 03, 2020 at 04:13:41PM +0200, Paul Cercueil wrote:
> > 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 at vger.kernel.org> # 4.10
> > Signed-off-by: Paul Cercueil <paul at crapouillou.net>
> 
> As discussed on irc this looks correct to me too.
> 
> Reviewed-by: Sam Ravnborg <sam at ravnborg.org>
> 
> 
> I will apply later, but let's wait and see if Noralf or others
> have any feedback first.
I finally went back to this patch, I missed it yesterday.
Applied to drm-misc-fixes with a stable 5.4+ tag.

	Sam

> > ---
> >  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);
> > -- 
> > 2.27.0
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