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From:   Souptick Joarder <jrdr.linux@gmail.com>
Date:   Mon, 30 Jul 2018 20:43:13 +0530
Message-ID: <CAFqt6zb_8a8G1DRRVpYDEjvzhgOzOK-O4K+oFzhVE-ELyX8Djw@mail.gmail.com>
Subject: Re: [PATCH] drm/rcar-du: Convert drm_atomic_helper_suspend/resume()
To:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        airlied@linux.ie, Daniel Vetter <daniel@ffwll.ch>
Cc:     Vaishali Thakkar <vthakkar@vaishalithakkar.in>,
        Ajit Linux <ajitn.linux@gmail.com>,
        dri-devel@lists.freedesktop.org, linux-renesas-soc@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Jul 30, 2018 at 7:54 PM, Laurent Pinchart
<laurent.pinchart@ideasonboard.com> wrote:
> Hi Souptick,
>
> On Monday, 30 July 2018 16:58:09 EEST Souptick Joarder wrote:
>> On Sun, Jul 29, 2018 at 1:50 AM, Laurent Pinchart wrote:
>> > 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@gmail.com>
>> >>>> Signed-off-by: Ajit Negi <ajitn.linux@gmail.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().
>
> My point is that if the fb cma helpers gets later extended with a feature that
> need special handling and suspend/resume time, with the
> drm_fbdev_cma_set_suspend_unlocked() function properly updated to take that
> feature into account, driver using those helpers but converted to
> drm_atomic_helper_suspend/resume() will break.
>
>> > 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 :)
>
> OK, if you remove the function completely then anyone wanting to extend the
> fbdev cma helpers in the way described above will notice that something will
> need to be done, so it's fine. Please thus make sure that you go all the way
> to removing that function.
>

Sure, once both the drivers are converted to use
drm_mode_config_helper_suspend/resume()
and goes into linus's tree, then we can remove it.

But will wait for some more feedback before concluding on this.

Dave/ Daniel, Would you like to add any feedback ?

>> >>> 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.
>> >>
>> >> >> -               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
>
>
>