linux-kernel - Re: [PATCH] drm: bridge: fix unmet dependency on DRM_KMS_HELPER for DRM_PANEL

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Date:   Tue, 26 Oct 2021 01:10:12 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Julian Braha <julianbraha@...il.com>
Cc:     robert.foss@...aro.org, a.hajda@...sung.com,
        narmstrong@...libre.com, jonas@...boo.se, jernej.skrabec@...il.com,
        airlied@...ux.ie, daniel@...ll.ch, jagan@...rulasolutions.com,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: bridge: fix unmet dependency on DRM_KMS_HELPER for
 DRM_PANEL_BRIDGE

Hi Julian,

On Mon, Oct 25, 2021 at 02:51:47PM -0400, Julian Braha wrote:
> On Monday, October 25, 2021 1:47:35 PM EDT you wrote:
> > On Mon, Oct 25, 2021 at 01:42:02PM -0400, Julian Braha wrote:
> > > When DRM_CHIPONE_ICN6211 is selected, and DRM_KMS_HELPER is not selected,
> > > Kbuild gives the following warning:
> > > 
> > > WARNING: unmet direct dependencies detected for DRM_PANEL_BRIDGE
> > >   Depends on [n]: HAS_IOMEM [=y] && DRM_BRIDGE [=y] && DRM_KMS_HELPER [=n]
> > >   Selected by [y]:
> > >   - DRM_CHIPONE_ICN6211 [=y] && HAS_IOMEM [=y] && DRM [=y] && DRM_BRIDGE [=y] && OF [=y]
> > > 
> > > This is because DRM_CHIPONE_ICN6211 selects DRM_PANEL_BRIDGE
> > > without depending on or selecting DRM_KMS_HELPER,
> > > despite DRM_PANEL_BRIDGE depending on DRM_KMS_HELPER.
> > > 
> > > This unmet dependency bug was detected by Kismet,
> > > a static analysis tool for Kconfig.
> > > Please advise if this is not the appropriate solution.
> > 
> > Shouldn't DRM_PANEL_BRIDGE select DRM_KMS_HELPER instead of depending on
> > it ?
> > 
> > > Fixes: ce517f18944e ("drm: bridge: Add Chipone ICN6211 MIPI-DSI to RGB bridge")
> > > Reviewed-by: Robert Foss <robert.foss@...aro.org>
> > > Signed-off-by: Julian Braha <julianbraha@...il.com>
> > > ---
> > >  drivers/gpu/drm/bridge/Kconfig | 1 +
> > >  1 file changed, 1 insertion(+)
> > > 
> > > diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
> > > index 431b6e12a81f..a630cb8fd1c8 100644
> > > --- a/drivers/gpu/drm/bridge/Kconfig
> > > +++ b/drivers/gpu/drm/bridge/Kconfig
> > > @@ -30,6 +30,7 @@ config DRM_CDNS_DSI
> > >  config DRM_CHIPONE_ICN6211
> > >  	tristate "Chipone ICN6211 MIPI-DSI/RGB Converter bridge"
> > >  	depends on OF
> > > +  select DRM_KMS_HELPER
> > >  	select DRM_MIPI_DSI
> > >  	select DRM_PANEL_BRIDGE
> > >  	help
> 
> Hi Laurent,
> 
> Either a "select" or a "depends" will resolve this issue,

Mixing "select" and "depends" usually lead to be results. DRM_KMS_HELPER
is a symbol that is mostly selected (I think there are a handful of
occurrences of "depends", which should probably be fixed).

> but most similar devices in this Kconfig file select DRM_KMS_HELPER.
> Is there something different about DRM_CHIPONE_ICN6211 that I have missed?

There isn't anything fundamentally different, but because DRM_KMS_HELPER
is meant to be selected and not depended on, I think we should fix that
for DRM_PANEL_BRIDGE, and it will fix the issue with
DRM_CHIPONE_ICN6211. The dependency on the KMS helpers come from
drm_panel_bridge.c, not from chipone-icn6211.c as far as I can tell, so
it would also be more correct.

-- 
Regards,

Laurent Pinchart