On 9/17/25 4:54 PM, Alexey Minnekhanov wrote: > On 17.09.2025 16:59, Konrad Dybcio wrote: >> On 9/17/25 3:09 AM, Paul Sajna wrote: >>> Add display dimensions for proper scaling >>> >>> Signed-off-by: Paul Sajna <[email protected]> >>> --- >>> arch/arm64/boot/dts/qcom/sdm845-lg-judyln.dts | 7 +++++++ >>> 1 file changed, 7 insertions(+) >>> >>> diff --git a/arch/arm64/boot/dts/qcom/sdm845-lg-judyln.dts >>> b/arch/arm64/boot/dts/qcom/sdm845-lg-judyln.dts >>> index >>> e84b45ed82fd13850ea7ec1f34ddac5b59fc1434..8c1692f86e6ceea7b718361965e78f95d39373bb >>> 100644 >>> --- a/arch/arm64/boot/dts/qcom/sdm845-lg-judyln.dts >>> +++ b/arch/arm64/boot/dts/qcom/sdm845-lg-judyln.dts >>> @@ -23,6 +23,13 @@ framebuffer@9d400000 { >>> format = "a8r8g8b8"; >>> lab-supply = <&lab>; >>> ibb-supply = <&ibb>; >>> + >>> + panel = <&fb_panel>; >>> + >>> + fb_panel: fb-panel { >>> + width-mm = <65>; >>> + height-mm = <140>; >> >> It'd be nicer if you moved these properties to the actual panel >> node (the DSI one) and referenced that one instead (I think that >> should work) >> >> Konrad >> > > Hi! > > First of all this code doesn't work well for upstream, because it causes > errors with dtbs checks like: > > framebuffer@9d400000 (simple-framebuffer): 'fb-panel' does not match any of > the regexes: '^[a-zA-Z0-9-]+-supply$', '^pinctrl-[0-9]+$' > > ^^ The subnode is not allowed by bindings. > > The whole reasoning for this little hack is that the upstream > recommended approach to solve the "unknown DPI" for framebuffer issue > is to put width-mm, height-mm into real panel node and and reference it > in simple-fb node - sonds very nice in theory, but also doesn't work > well in practice, and explanation why will take a bit longer, please > bear with me for a minute. > > If we do as recommended, device tree structure will look like this: > > framebuffer@9d400000 { > ... > panel = <&display_panel>; > }; > > soc@0 { > .... > > mdss { > ... > dsi0 { > ... > display_panel: panel@0 { > reg = <0>; > compatible = "lg,sw49410"; > ... > width-mm = <65>; > height-mm = <140>; > }; > ... > > Then, to my understanding, due to how fw-devlink works, the panel=<&..> > link from simplefb node to display_panel node creates a probe-time > dependency, so that the whole display stack probes first: MDSS, DSI > controller, maybe even Adreno GPU, *AND* panel all probe first, thus > making the mere existence of simple-framebuffer pointless. > > Additionally, simple-framebuffer probes succesfully after that, > creating "second GPU" entry in as /dev/dri/card1 making it look like > system has 2 GPUS, which confuses almost every window manager in > userspace later. Normally, if simplefb probes first, it gets unloaded > and replaced by MDSS and does not cause any chaos. In the end the whole > situation looks even more silly than the fake panel subnode hack. > > Therefore for upstream I'd recommend to just drop any fb-panel hacks and > to not use panel=<&...> with reference to real panel either. > > It would all be much much easier if we could just specify width-mm/ > height-mm directly in simplefb node, but DT maintainers rejected that idea.
Would adding post-init-providers = <&real_panel> help? Konrad
