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Date:   Fri, 23 Jun 2023 20:52:27 +0300
From:   Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To:     Geert Uytterhoeven <geert@linux-m68k.org>
Cc:     Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>,
        David Airlie <airlied@gmail.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        Magnus Damm <magnus.damm@gmail.com>,
        dri-devel@lists.freedesktop.org, linux-renesas-soc@vger.kernel.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 06/39] drm: renesas: shmobile: Add support for Runtime PM
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Hi Geert,

On Fri, Jun 23, 2023 at 07:41:36PM +0200, Geert Uytterhoeven wrote:
> On Fri, Jun 23, 2023 at 5:34 PM Laurent Pinchart wrote:
> > On Fri, Jun 23, 2023 at 05:22:45PM +0200, Geert Uytterhoeven wrote:
> > > On Fri, Jun 23, 2023 at 5:11 PM Laurent Pinchart wrote:
> > > > On Fri, Jun 23, 2023 at 06:07:44PM +0300, Laurent Pinchart wrote:
> > > > > On Thu, Jun 22, 2023 at 11:21:18AM +0200, Geert Uytterhoeven wrote:
> > > > > > The SH-Mobile LCD Controller is part of a PM Domain on all relevant SoCs
> > > > > > (clock domain on all, power domain on some).  Hence it may not be
> > > > > > sufficient to manage the LCDC module clock explicitly (e.g. if the
> > > > > > selected clock source differs from SHMOB_DRM_CLK_BUS).
> > > > > >
> > > > > > Fix this by using Runtime PM instead.
> > > > > >
> > > > > > Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
> > > > > > ---
> > > > > >  drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c | 11 ++++++++++-
> > > > > >  drivers/gpu/drm/renesas/shmobile/shmob_drm_drv.c  |  5 +++++
> > > > > >  2 files changed, 15 insertions(+), 1 deletion(-)
> > > > > >
> > > > > > diff --git a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > > > > > index fbfd906844da490c..84dbf35025d7be63 100644
> > > > > > --- a/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > > > > > +++ b/drivers/gpu/drm/renesas/shmobile/shmob_drm_crtc.c
> > > > > > @@ -9,6 +9,7 @@
> > > > > >
> > > > > >  #include <linux/backlight.h>
> > > > > >  #include <linux/clk.h>
> > > > > > +#include <linux/pm_runtime.h>
> > > > > >
> > > > > >  #include <drm/drm_crtc.h>
> > > > > >  #include <drm/drm_crtc_helper.h>
> > > > > > @@ -170,10 +171,16 @@ static void shmob_drm_crtc_start(struct shmob_drm_crtc *scrtc)
> > > > > >     if (WARN_ON(format == NULL))
> > > > > >             return;
> > > > > >
> > > > > > +   ret = pm_runtime_resume_and_get(sdev->dev);
> > > > > > +   if (ret)
> > > > > > +           return;
> > > > > > +
> > > > > >     /* Enable clocks before accessing the hardware. */
> > > > > >     ret = shmob_drm_clk_on(sdev);
> > > > >
> > > > > This would be best located in the runtime PM resume handler. Same for
> > > > > disabling clocks in the runtime PM suspend handler.
> > > >
> > > > The driver should then depend on CONFIG_PM. There's no indirect
> > > > dependency through CONFIG_DRM as far as I can tell, but there's one
> > > > through ARCH_SHMOBILE. This then got me puzzled, as ARCH_SHMOBILE is
> > > > defined in arch/sh/Kconfig, and this driver depends on ARM. Am I missing
> > > > something ?
> > >
> > > Vommit 4bd65789ba847f39 ("drm: shmobile: Make DRM_SHMOBILE visible on
> > > Renesas SoC platforms") in drm-next:
> > >
> > > -       depends on DRM && ARM
> > > -       depends on ARCH_SHMOBILE || COMPILE_TEST
> > > +       depends on DRM
> > > +       depends on ARCH_RENESAS || ARCH_SHMOBILE || COMPILE_TEST
> >
> > That's better indeed :-)
> >
> > A dependency on CONFIG_PM is still needed as ARCH_RENESAS doesn't depend
> > on it.
> 
> ARCH_RMOBILE selects PM, so PM will be enabled on affected platforms.

Which also means that you will never test compilation without CONFIG_PM,
while bots will. There's a risk of introducing compilation warnings.

-- 
Regards,

Laurent Pinchart