Re: [PATCH] drm: rcar_du: DRM_RCAR_DU optionally depends on RCAR_MIPI_DSI

[Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>]

Quoting Javier Martinez Canillas (2022-11-03 11:53:14)
> Hello Kieran,
> 
> On 11/3/22 11:59, Kieran Bingham wrote:
> > 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@infradead.org>
> >>> Cc: Tomi Valkeinen <tomi.valkeinen+renesas@ideasonboard.com>
> >>> Cc: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> >>> Cc: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
> >>> Cc: LUU HOAI <hoai.luu.ub@renesas.com>
> >>> Cc: dri-devel@lists.freedesktop.org
> >>> Cc: linux-renesas-soc@vger.kernel.org
> >>> Cc: David Airlie <airlied@gmail.com>
> >>> Cc: Daniel Vetter <daniel@ffwll.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
> >
> 
> What this Kconfig expression is saying is that it depends on DRM_RCAR_MIPI_DSI=y
> if DRM_RCAR_DU=y and DRM_RCAR_MIPI_DSI=m if DRM_RCAR_DU=m. But that the it can
> also be satisfied if is not set DRM_RCAR_MIPI_DSI.
> 
> This is usually used to make sure that you don't end with a configuration where
> DRM_RCAR_MIPI_DSI=y and DRM_RCAR_DU=m or DRM_RCAR_MIPI_DSI=m and DRM_RCAR_DU=y.
> 
> Randy, I think that it's more idiomatic though to it express as following:
> 
> depends on DRM_RCAR_MIPI_DSI || !DRM_RCAR_MIPI_DSI

Ok - thanks, so it's the module part that breaks. I never build modules,
always builtin - so it doesn't hit me ;-)

Anyway - it certainly makes sense now I think so either as posted, or
with the idiomatic proposal from Javier:

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> 
> -- 
> Best regards,
> 
> Javier Martinez Canillas
> Core Platforms
> Red Hat
>