Am Samstag, den 19.02.2022, 09:37 +0000 schrieb Christoph Niedermaier: > From: Max Krummenacher [mailto:max.oss.09@xxxxxxxxx] > Sent: Wednesday, February 9, 2022 2:14 PM > > Hi > > > > Am Mittwoch, den 09.02.2022, 00:52 +0100 schrieb Marek Vasut: > > > On 2/8/22 22:27, Christoph Niedermaier wrote: > > > > From: Laurent Pinchart [mailto:laurent.pinchart@xxxxxxxxxxxxxxxx] > > > > Sent: Thursday, February 3, 2022 12:46 AM > > > > > Hi Christoph, > > > > > > > > > > > > > Hi Laurent, > > > > > > > > > On Tue, Feb 01, 2022 at 12:07:17PM +0100, Christoph Niedermaier wrote: > > > > > > Without the data-mapping devicetree property my display won't > > > > > > work properly. It is flickering, because the bus flags won't > > > > > > be assigned without a defined bus format by the imx parallel > > > > > > display driver. There was a discussion about the removal [1] > > > > > > and an agreement that a better solution is needed, but it is > > > > > > missing so far. So what would be the better approach? > > > > > > > > > > > > [1] https://patchwork.freedesktop.org/patch/357659/?series=74705&rev=1 > > > > > > > > > > > > This reverts commit d021d751c14752a0266865700f6f212fab40a18c. > > > > > > > > > > > > Signed-off-by: Christoph Niedermaier <cniedermaier@xxxxxxxxxxxxxxxxxx> > > > > > > Cc: Marek Vasut <marex@xxxxxxx> > > > > > > Cc: Sam Ravnborg <sam@xxxxxxxxxxxx> > > > > > > Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx> > > > > > > Cc: Maxime Ripard <mripard@xxxxxxxxxx> > > > > > > Cc: Philipp Zabel <p.zabel@xxxxxxxxxxxxxx> > > > > > > Cc: David Airlie <airlied@xxxxxxxx> > > > > > > Cc: Daniel Vetter <daniel@xxxxxxxx> > > > > > > Cc: Shawn Guo <shawnguo@xxxxxxxxxx> > > > > > > Cc: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx> > > > > > > Cc: Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx> > > > > > > Cc: Fabio Estevam <festevam@xxxxxxxxx> > > > > > > Cc: NXP Linux Team <linux-imx@xxxxxxx> > > > > > > Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx > > > > > > To: dri-devel@xxxxxxxxxxxxxxxxxxxxx > > > > > > --- > > > > > > drivers/gpu/drm/panel/panel-simple.c | 11 +++++++++++ > > > > > > 1 file changed, 11 insertions(+) > > > > > > > > > > > > diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c > > > > > > index 3c08f9827acf..2c683d94a3f3 100644 > > > > > > --- a/drivers/gpu/drm/panel/panel-simple.c > > > > > > +++ b/drivers/gpu/drm/panel/panel-simple.c > > > > > > @@ -453,6 +453,7 @@ static int panel_dpi_probe(struct device *dev, > > > > > > struct panel_desc *desc; > > > > > > unsigned int bus_flags; > > > > > > struct videomode vm; > > > > > > + const char *mapping; > > > > > > int ret; > > > > > > > > > > > > np = dev->of_node; > > > > > > @@ -477,6 +478,16 @@ static int panel_dpi_probe(struct device *dev, > > > > > > of_property_read_u32(np, "width-mm", &desc->size.width); > > > > > > of_property_read_u32(np, "height-mm", &desc->size.height); > > > > > > > > > > > > + of_property_read_string(np, "data-mapping", &mapping); > > > > > > + if (!strcmp(mapping, "rgb24")) > > > > > > + desc->bus_format = MEDIA_BUS_FMT_RGB888_1X24; > > > > > > + else if (!strcmp(mapping, "rgb565")) > > > > > > + desc->bus_format = MEDIA_BUS_FMT_RGB565_1X16; > > > > > > + else if (!strcmp(mapping, "bgr666")) > > > > > > + desc->bus_format = MEDIA_BUS_FMT_RGB666_1X18; > > > > > > + else if (!strcmp(mapping, "lvds666")) > > > > > > + desc->bus_format = MEDIA_BUS_FMT_RGB666_1X24_CPADHI; > > > > > > > > > > You're right that there's an issue, but a revert isn't the right option. > > > > > The commit you're reverting never made it in a stable release, because > > > > > it was deemed to not be a good enough option. > > > > > > > > > > First of all, any attempt to fix this should include an update to the DT > > > > > binding. Second, as this is about DPI panels, the LVDS option should be > > > > > dropped. Finally, I've shared some initial thoughts in [1], maybe you > > > > > can reply to that e-mail to continue the discussion there ? > > > > > > > > According to your thoughts in [1] you mean that the bus format should be > > > > build out of the devicetree properties bus-width and data-shift. It would > > > > be possible for evenly structured busses like RGB888_1X24 and RGB666_1X18, > > > > but what about a bus like RGB565_1X16, where each color has different > > > > bus width. Also the order of the colors should be defined to differ > > > > between busses like RGB888_1X24 and GBR888_1X24. > > > > Are there any ideas how can this be covered? > > > > > > Maybe with props like these ? > > > > > > channel-width -- width of each color channel > > > channel-shift -- shift of each color channel > > > channel-map -- mapping of each color channel > > > > > > So for RGB888 > > > channel-width = <8 8 8>; > > > channel-shift = <0 0 0>; > > > channel-map = "RGB"; // or something ? > > > > > > For BGR565 panel connected to RGB24 scanout > > > channel-width = <5 6 5>; > > > channel-shift = <3 2 3>; > > > channel-map = "BGR"; // or something ? > > > > > > For BGR565 panel connected to RGB565 scanout > > > channel-width = <5 6 5>; > > > channel-shift = <0 0 0>; > > > channel-map = "BGR"; // or something ? > > > > > > > To me this looks like it goes into the wrong direction. > > The goal is to set bus_format to one of the > > possible enum values. > > Using such a generic approach it would be possible to request bus > > formats for which no enum value is currently defined, i.e. the > > BGR565 example does not have a matching bus_format in > > media-bus-format.h. > > > > What about keeping the solution which the revert would give. > > Optionally with a changed property name s/data-mapping/bus-format/ > > and a changed list of allowed strings to better match between the > > dt string and the enum name, i.e. s/"rgb24"/"RGB888_1X24"/. > > This would allow to extend DT binding and > > code to possible newly > > required values like e.g. MEDIA_BUS_FMT_BGR888_1X24. > > > > Alternatively one could use the bus-width and data-shift > > properties and allow for (bus-width + data-shift) to be one > > of 16, 18, 24 and assume RGB. I.e. one could only specify > > MEDIA_BUS_FMT_RGB565_1X16, MEDIA_BUS_FMT_RGB666_1X18, > > MEDIA_BUS_FMT_RGB888_1X24 respectively. > > > > Max > > > > Hi Laurent, > > In which direction should it go to find an acceptable solution? Hi I sent a proposal as RFC to show how this could look in the implementation. https://lore.kernel.org/all/20220222084723.14310-1-max.krummenacher@xxxxxxxxxxx/ Max > > Regards > Christoph
