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

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Date:   Mon, 30 Jul 2018 19:28:09 +0530
From:   Souptick Joarder <jrdr.linux@...il.com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.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()

On Sun, Jul 29, 2018 at 1:50 AM, Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> 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.

No, any extention of drm_fbdev_cma_set_suspend_unlocked() will not have
any impact on driver because with this patch we will be retaining the original
suspend/resume logic of the rcar-du driver and further this driver is not going
to use drm_fbdev_cma_set_suspend_unlocked().


> 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().

The consumers of drm_fbdev_cma_set_suspend_unlocked() are -
drivers/gpu/drm/arm/hdlcd_drv.c
drivers/gpu/drm/drm_fb_cma_helper.c

and both will be converted to use API drm_mode_config_helper_suspend/resume().
As there will be no more consumer of drm_fbdev_cma_set_suspend_unlocked() , we
can remove this wrapper API forever :)

>
>> > 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.

Sure, I will remove it in v2.

>
>> >> -       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
>
>
>