Re: [PATCH] Revert "drm/bridge: lt9611: Do not generate HFP/HBP/HSA and EOT packet"

[Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>]

On 02/08/2023 21:45, Marek Vasut wrote:
> On 8/2/23 20:16, Dmitry Baryshkov wrote:
> > On Wed, 2 Aug 2023 at 20:34, Marek Vasut <marex@xxxxxxx> wrote:
> > > On 8/2/23 15:38, Dmitry Baryshkov wrote:
> > > > On 02/08/2023 11:52, Neil Armstrong wrote:
> > > > > This reverts commit [1] to fix display regression on the 
> > > > > Dragonboard 845c
> > > > > (SDM845) devboard.
> > > > >
> > > > > There's a mismatch on the real action of the following flags:
> > > > > - MIPI_DSI_MODE_VIDEO_NO_HSA
> > > > > - MIPI_DSI_MODE_VIDEO_NO_HFP
> > > > > - MIPI_DSI_MODE_VIDEO_NO_HBP
> > > > > which leads to a non-working display on qcom platforms.
> > > > >
> > > > > [1] 8ddce13ae696 ("drm/bridge: lt9611: Do not generate HFP/HBP/HSA and
> > > > > EOT packet")
> > > > >
> > > > > Cc: Marek Vasut <marex@xxxxxxx>
> > > > > Cc: Robert Foss <rfoss@xxxxxxxxxx>
> > > > > Cc: Jagan Teki <jagan@xxxxxxxxxxxxxxxxxxxx>
> > > > > Cc: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx>
> > > > > Cc: Abhinav Kumar <quic_abhinavk@xxxxxxxxxxx>
> > > > > Fixes: 8ddce13ae69 ("drm/bridge: lt9611: Do not generate HFP/HBP/HSA
> > > > > and EOT packet")
> > > > > Reported-by: Amit Pundir <amit.pundir@xxxxxxxxxx>
> > > > > Link:
> > > > > https://lore.kernel.org/r/CAMi1Hd0TD=2z_=bcDrht3H_wiLvAFcv8Z-U_r_KUOoeMc6UMjw@xxxxxxxxxxxxxx/
> > > > > Signed-off-by: Neil Armstrong <neil.armstrong@xxxxxxxxxx>
> > > > > ---
> > > > >    drivers/gpu/drm/bridge/lontium-lt9611.c | 4 +---
> > > > >    1 file changed, 1 insertion(+), 3 deletions(-)
> > > > Acked-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxx> #fix db845c
> > > >
> > > > The boards broken by [1] are used in production by different parties
> > > > since 5.10, breaking them doesn't seem more acceptable than breaking 
> > > > the
> > > > new out-of-tree iMX8m hardware.
> > >
> > > The MX8M is also in-tree, so this does not apply.
> >
> > v6.5-rc4:
> >
> > $ git grep lontium,lt9611 | grep -v 9611uxc
> > Documentation/devicetree/bindings/display/bridge/lontium,lt9611.yaml:$id:
> > http://devicetree.org/schemas/display/bridge/lontium,lt9611.yaml#
> > Documentation/devicetree/bindings/display/bridge/lontium,lt9611.yaml:
> >      - lontium,lt9611
> > Documentation/devicetree/bindings/display/bridge/lontium,lt9611.yaml:
> >        compatible = "lontium,lt9611";
> > arch/arm64/boot/dts/qcom/sdm845-db845c.dts: compatible = 
> > "lontium,lt9611";
> > drivers/gpu/drm/bridge/lontium-lt9611.c: { "lontium,lt9611", 0 },
> > drivers/gpu/drm/bridge/lontium-lt9611.c: { .compatible = 
> > "lontium,lt9611" },
> >
> > next-20230802:
> >
> > $ git grep lontium,lt9611 | grep -v 9611uxc
> > Documentation/devicetree/bindings/display/bridge/lontium,lt9611.yaml:$id:
> > http://devicetree.org/schemas/display/bridge/lontium,lt9611.yaml#
> > Documentation/devicetree/bindings/display/bridge/lontium,lt9611.yaml:
> >      - lontium,lt9611
> > Documentation/devicetree/bindings/display/bridge/lontium,lt9611.yaml:
> >        compatible = "lontium,lt9611";
> > arch/arm64/boot/dts/qcom/sdm845-db845c.dts: compatible = 
> > "lontium,lt9611";
> > drivers/gpu/drm/bridge/lontium-lt9611.c: { "lontium,lt9611", 0 },
> > drivers/gpu/drm/bridge/lontium-lt9611.c: { .compatible = 
> > "lontium,lt9611" },
> >
> > Your device is not in the tree. Your commit broke existing users.
>
> These devices are in tree:
> arch/arm64/boot/dts/freescale/imx8mm-data-modul-edm-sbc.dts
> arch/arm64/boot/dts/freescale/imx8mp-data-modul-edm-sbc.dts
>
> The LT9211 and LT9611 are both expansion modules handled by DTOs and 
> bound to the DSIM (which is also in tree).

And they DT for them is not in the tree, that was my point. You have 
broken the existing user for the DTBO that is not present even in 
linux-next.

> > Can we please end the argument, land the fix (this revert) for 6.5 and
> > work on the solution for 6.6 or 6.7?
>
> I would much prefer a solution which does not break my existing use 
> case. It is still not even clear whether the problem really is on MX8M 
> side at all, or whether it is QCOM misinterpreting flags. I cannot debug 
> the later, since I have no access to that platform, nor its documentation.

You can get the RB1 for $199 and check the DSI behaviour on that 
platform. It has newer bridge, but the DSI controller is (mostly) the same.

--
With best wishes
Dmitry