linux-kernel - Re: [PATCH v8 05/18] drm/bridge: Move legacy bridge driver out of imx directory for multi-platform use

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Message-ID: <20260203140945.GC12013@killaraus>
Date: Tue, 3 Feb 2026 16:09:45 +0200
From: Laurent Pinchart <laurent.pinchart@...asonboard.com>
To: Luca Ceresoli <luca.ceresoli@...tlin.com>
Cc: Damon Ding <damon.ding@...k-chips.com>, andrzej.hajda@...el.com,
	neil.armstrong@...aro.org, rfoss@...nel.org,
	dmitry.baryshkov@....qualcomm.com, jonas@...boo.se,
	jernej.skrabec@...il.com, maarten.lankhorst@...ux.intel.com,
	mripard@...nel.org, tzimmermann@...e.de, airlied@...il.com,
	simona@...ll.ch, shawnguo@...nel.org, s.hauer@...gutronix.de,
	kernel@...gutronix.de, festevam@...il.com, inki.dae@...sung.com,
	sw0312.kim@...sung.com, kyungmin.park@...sung.com, krzk@...nel.org,
	alim.akhtar@...sung.com, jingoohan1@...il.com,
	p.zabel@...gutronix.de, hjc@...k-chips.com, heiko@...ech.de,
	andy.yan@...k-chips.com, dianders@...omium.org,
	m.szyprowski@...sung.com, jani.nikula@...el.com,
	linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
	imx@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org,
	linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH v8 05/18] drm/bridge: Move legacy bridge driver out of
 imx directory for multi-platform use

On Tue, Feb 03, 2026 at 11:11:50AM +0100, Luca Ceresoli wrote:
> On Tue Feb 3, 2026 at 2:31 AM CET, Damon Ding wrote:
> > On 2/2/2026 10:54 AM, Damon Ding wrote:
> >> On 1/31/2026 8:33 PM, Luca Ceresoli wrote:
> >>> On Wed Dec 17, 2025 at 10:33 AM CET, Damon Ding wrote:
> >>>> As suggested by Dmitry, the DRM legacy bridge driver can be pulled
> >>>> out of imx/ subdir for multi-platform use. The driver is also renamed
> >>>> to make it more generic and suitable for platforms other than i.MX.
> >>>>
> >>>> Signed-off-by: Damon Ding <damon.ding@...k-chips.com>
> >>>> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
> >>>> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> >>>>
> >>>> ---
> >>>>
> >>>> Changes in v7:
> >>>> - Rename legacy-bridge to of-display-mode-bridge.
> >>>> - Remove unnecessary API drm_bridge_is_legacy().
> >>>
> >>> ...
> >>>
> >>>> --- a/drivers/gpu/drm/bridge/Kconfig
> >>>> +++ b/drivers/gpu/drm/bridge/Kconfig
> >>>> @@ -244,6 +244,16 @@ config DRM_NXP_PTN3460
> >>>>       help
> >>>>         NXP PTN3460 eDP-LVDS bridge chip driver.
> >>>>
> >>>> +config DRM_OF_DISPLAY_MODE_BRIDGE
> >>>> +    tristate
> >>>> +    depends on DRM_BRIDGE && OF
> >>>> +    help
> >>>> +      This is a DRM bridge implementation that uses
> >>>> of_get_drm_display_mode
> >>>> +      to acquire display mode.
> >>>> +
> >>>> +      Newer designs should not use this bridge and should use proper
> >>>> panel
> >>>> +      driver instead.
> >>>
> >>> "Newer designs should not use this bridge", but in patch 8 you are
> >>> introducing a new use ot devm_drm_of_display_mode_bridge(). Shouldn't you
> >>> instead "use proper panel driver instead" in patch 8?
> >>>
> >>> Can you point to the conversation where the converstaion where Dmitry
> >>> suggested this change? Maybe it already contains the answer to my
> >>> qustion. Also adding a link to that conversation in the commit message
> >>> woule be useful.
> >>>
> >>
> >> First of all, thanks for your reviews on this patch series.
> >>
> >> link: https://lore.kernel.org/all/
> >> xwenycscalzdlpuxytorbiyvej3k7pv3lhxwtadilxq65ipwsv@...xm53w5e22/
> >>
> >> I think it may be a misleading issue caused by directly copying the
> >> previous Kconfig description. Now that the new
> >> devm_drm_of_display_mode_bridge() helper has been added, drivers using
> >> the panel-bridge framework can rely on it to maintain compatibility with
> >> legacy display mode parsing.
> 
> Ah, I think I got the point: the mode description in device tree is legacy,
> but the driver itself is not legacy and will be current until we need to
> support legacy device tree. Correct?
> 
> If that's correct, this patch looks OK to me with a new Kconfig help text.

The devm_drm_of_display_mode_bridge() function needs documentation
though, with a warning that tells it must not be used in new drivers.
Catching new users in checkpatch.pl (or somewhere else) would be ideal.

I would also not create a separate module for this and move the function
to drm_bridge.c, but I don't mind that much if the consensus is that a
separate module is better.

> >> It would be better to update the comment as follows:
> >>
> >> This is a DRM bridge implementation that uses of_get_drm_display_mode to
> >> acquire display mode.
> >>
> >> It exists for compatibility with legacy display mode parsing, in order
> >> to conform to the panel-bridge framework.
> >>
> >
> > Dmitry, what's you take on this?
> 
> Dmitry's opinion would be much more relevant than mine. I don't know much
> myself about this driver.

-- 
Regards,

Laurent Pinchart