linux-kernel - Re: [PATCH] drm/rcar-du: Convert drm_atomic_helper

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Message-ID: <10502231.oSnn9dME1M@avalon>
Date:   Sat, 28 Jul 2018 23:20:07 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Souptick Joarder <jrdr.linux@...il.com>
Cc:     Vaishali Thakkar <vthakkar@...shalithakkar.in>, airlied@...ux.ie,
        Ajit Linux <ajitn.linux@...il.com>,
        dri-devel@...ts.freedesktop.org, linux-renesas-soc@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH] drm/rcar-du: Convert drm_atomic_helper_suspend/resume()

Hi Souptick,

Thank you for the patch.

On Saturday, 28 July 2018 21:50:58 EEST Souptick Joarder wrote:
> On Sat, Jul 28, 2018 at 11:20 PM, Vaishali Thakkar wrote:
> > On Sat, Jul 28, 2018 at 9:10 PM, Souptick Joarder wrote:
> >> convert drm_atomic_helper_suspend/resume() to use
> >> drm_mode_config_helper_suspend/resume().
> > 
> > Hi Souptick,
> > 
> > Thanks for your patch.
> > 
> >> Signed-off-by: Souptick Joarder <jrdr.linux@...il.com>
> >> Signed-off-by: Ajit Negi <ajitn.linux@...il.com>
> >> ---
> >> 
> >>  drivers/gpu/drm/rcar-du/rcar_du_drv.c | 21 ++-------------------
> >>  1 file changed, 2 insertions(+), 19 deletions(-)
> >> 
> >> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >> b/drivers/gpu/drm/rcar-du/rcar_du_drv.c index 02aee6c..288220f 100644
> >> --- a/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >> +++ b/drivers/gpu/drm/rcar-du/rcar_du_drv.c
> >> @@ -357,32 +357,15 @@ static void rcar_du_lastclose(struct drm_device
> >> *dev)
> >> 
> >>  static int rcar_du_pm_suspend(struct device *dev)
> >>  {
> >>         struct rcar_du_device *rcdu = dev_get_drvdata(dev);
> >> -       struct drm_atomic_state *state;
> >> 
> >> -       drm_kms_helper_poll_disable(rcdu->ddev);
> >> -       drm_fbdev_cma_set_suspend_unlocked(rcdu->fbdev, true);
> >> -
> >> -       state = drm_atomic_helper_suspend(rcdu->ddev);
> >> -       if (IS_ERR(state)) {
> >> -               drm_fbdev_cma_set_suspend_unlocked(rcdu->fbdev, false);
> > 
> > I don't think we can use drm_mode_config_helper_(suspend/resume)
> > API here as this file uses CMA functions.
> 
> drm_fbdev_cma_set_suspend_unlocked() is wrapper function which
> invokes drm_fb_helper_set_suspend_unlocked().
> 
> Where the new API drm_mode_config_helper_suspend/resume() directly invokes
> drm_fb_helper_set_suspend_unlocked(). So it is safe to replace exiting
> code with API drm_mode_config_helper_suspend/resume().

I agree that they're functionally equivalent for now, but what if 
drm_fbdev_cma_set_suspend_unlocked() gets extended later ? This change risks 
introducing a breakage that could could unnoticed at that point. At the very 
least you should add a comment in drm_fbdev_cma_set_suspend_unlocked() to 
explain that any extension of the function should also address all drivers 
using drm_mode_config_helper_suspend() and drm_mode_config_helper_resume().

> > And from git grep it seems that there are very few drivers using it at the
> > moment, so not sure if introducing new API functions similar to 
> > drm_mode_config will make sense or not.
> 
> https://www.kernel.org/doc/html/latest/gpu/todo.html
> 
> It was picked up from TODO list after discussing with
> Daniel.
> 
> > Thanks.
> > 
> >> -               drm_kms_helper_poll_enable(rcdu->ddev);
> >> -               return PTR_ERR(state);
> >> -       }
> >> -
> >> -       rcdu->suspend_state = state;

Additionally, I think you can remove the suspend_state field from the rcdu 
structure.

> >> -       return 0;
> >> +       return drm_mode_config_helper_suspend(rcdu->ddev);
> >>  }
> >>  
> >>  static int rcar_du_pm_resume(struct device *dev)
> >>  {
> >>         struct rcar_du_device *rcdu = dev_get_drvdata(dev);
> >> 
> >> -       drm_atomic_helper_resume(rcdu->ddev, rcdu->suspend_state);
> >> -       drm_fbdev_cma_set_suspend_unlocked(rcdu->fbdev, false);
> >> -       drm_kms_helper_poll_enable(rcdu->ddev);
> >> -
> >> -       return 0;
> >> +       return drm_mode_config_helper_resume(rcdu->ddev);
> >>  }
> >>  #endif

-- 
Regards,

Laurent Pinchart