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Wed, 09 Feb 2022 05:14:02 -0800 (PST) Message-ID: <78357e75dede2a7bff95126ff35784929335e918.camel@gmail.com> Subject: Re: [RFC][PATCH] Revert "drm/panel-simple: drop use of data-mapping property" From: Max Krummenacher To: Marek Vasut , Christoph Niedermaier , Laurent Pinchart Cc: "dri-devel@lists.freedesktop.org" , Sam Ravnborg , Maxime Ripard , Philipp Zabel , David Airlie , Daniel Vetter , Shawn Guo , Sascha Hauer , Pengutronix Kernel Team , Fabio Estevam , NXP Linux Team , "linux-arm-kernel@lists.infradead.org" , DenysDrozdov Date: Wed, 09 Feb 2022 14:14:01 +0100 In-Reply-To: References: <20220201110717.3585-1-cniedermaier@dh-electronics.com> <4a2f4707c03d4509aa5f3a388cbfbe04@dh-electronics.com> User-Agent: Evolution 3.34.4 MIME-Version: 1.0 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20220209_051404_539254_B3E6A215 X-CRM114-Status: GOOD ( 48.34 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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@ideasonboard.com] > > 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 > > > > Cc: Marek Vasut > > > > Cc: Sam Ravnborg > > > > Cc: Laurent Pinchart > > > > Cc: Maxime Ripard > > > > Cc: Philipp Zabel > > > > Cc: David Airlie > > > > Cc: Daniel Vetter > > > > Cc: Shawn Guo > > > > Cc: Sascha Hauer > > > > Cc: Pengutronix Kernel Team > > > > Cc: Fabio Estevam > > > > Cc: NXP Linux Team > > > > Cc: linux-arm-kernel@lists.infradead.org > > > > To: dri-devel@lists.freedesktop.org > > > > --- > > > > 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 > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel