linux-kernel - Re: [PATCH] drm: rcar_du: DRM_RCAR_DU optionally depends on RCAR_MIPI

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Message-ID: <166747314442.3962897.9754510086268412956@Monstersaurus>
Date:   Thu, 03 Nov 2022 10:59:04 +0000
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Randy Dunlap <rdunlap@...radead.org>, linux-kernel@...r.kernel.org
Cc:     Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>,
        LUU HOAI <hoai.luu.ub@...esas.com>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm: rcar_du: DRM_RCAR_DU optionally depends on RCAR_MIPI_DSI

Hi Randy,

Quoting Randy Dunlap (2022-11-03 06:06:45)
> ping. I have verified (on linux-next-20221103) that this is still needed.
> Thanks.
> 
> On 10/18/22 11:18, Randy Dunlap wrote:
> > When CONFIG_DRM_RCAR_DU=y and CONFIG_DRM_RCAR_MIPI_DSI=m, calls
> > from the builtin driver to the mipi driver fail due to linker
> > errors.
> > Since the RCAR_MIPI_DSI driver is not always required, fix the
> > build error by making DRM_RCAR_DU optionally depend on the
> > RCAR_MIPI_DSI Kconfig symbol. This prevents the problematic
> > kconfig combination without requiring that RCAR_MIPI_DSI always
> > be enabled.
> > 
> > aarch64-linux-ld: drivers/gpu/drm/rcar-du/rcar_du_crtc.o: in function `rcar_du_crtc_atomic_enable':
> > rcar_du_crtc.c:(.text+0x3a18): undefined reference to `rcar_mipi_dsi_pclk_enable'
> > aarch64-linux-ld: drivers/gpu/drm/rcar-du/rcar_du_crtc.o: in function `rcar_du_crtc_atomic_disable':
> > rcar_du_crtc.c:(.text+0x47cc): undefined reference to `rcar_mipi_dsi_pclk_disable'
> > 
> > Fixes: 957fe62d7d15 ("drm: rcar-du: Fix DSI enable & disable sequence")
> > Signed-off-by: Randy Dunlap <rdunlap@...radead.org>
> > Cc: Tomi Valkeinen <tomi.valkeinen+renesas@...asonboard.com>
> > Cc: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> > Cc: Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
> > Cc: LUU HOAI <hoai.luu.ub@...esas.com>
> > Cc: dri-devel@...ts.freedesktop.org
> > Cc: linux-renesas-soc@...r.kernel.org
> > Cc: David Airlie <airlied@...il.com>
> > Cc: Daniel Vetter <daniel@...ll.ch>
> > ---
> >  drivers/gpu/drm/rcar-du/Kconfig |    1 +
> >  1 file changed, 1 insertion(+)
> > 
> > diff -- a/drivers/gpu/drm/rcar-du/Kconfig b/drivers/gpu/drm/rcar-du/Kconfig
> > --- a/drivers/gpu/drm/rcar-du/Kconfig
> > +++ b/drivers/gpu/drm/rcar-du/Kconfig
> > @@ -4,6 +4,7 @@ config DRM_RCAR_DU
> >       depends on DRM && OF
> >       depends on ARM || ARM64
> >       depends on ARCH_RENESAS || COMPILE_TEST
> > +     depends on DRM_RCAR_MIPI_DSI || DRM_RCAR_MIPI_DSI=n

Please forgive my ignorance, but I don't understand how this works.
Could you explain what this is doing please?

I know you've explained above that it fixes it to optionally depend on
DRM_RCAR_MIPI_DSI ... but it's not making sense to me.

To me - this is saying we depend on DRM_RCAR_MIPI_DSI being enabled, or
not being enabled ... ? Which is like saying if (0 || 1) ?

I'm guessing I'm missing something obvious :-S

--
Kieran


> >       select DRM_KMS_HELPER
> >       select DRM_GEM_DMA_HELPER
> >       select VIDEOMODE_HELPERS
> 
> -- 
> ~Randy