linux-kernel - Re: [PATCH 02/10] drm/tidss: Use PM autosuspend

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Message-ID: <20231105225330.GA15635@pendragon.ideasonboard.com>
Date:   Mon, 6 Nov 2023 00:53:30 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
Cc:     Aradhya Bhatia <a-bhatia1@...com>,
        Devarsh Thakkar <devarsht@...com>,
        Jyri Sarha <jyri.sarha@....fi>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        Sakari Ailus <sakari.ailus@....fi>
Subject: Re: [PATCH 02/10] drm/tidss: Use PM autosuspend

Hi Tomi,

CC'ing Sakari for his expertise on runtime PM (I think he will soon
start wishing he would be ignorant in this area).

On Thu, Nov 02, 2023 at 08:34:45AM +0200, Tomi Valkeinen wrote:
> On 01/11/2023 15:54, Laurent Pinchart wrote:
> > On Wed, Nov 01, 2023 at 11:17:39AM +0200, Tomi Valkeinen wrote:
> >> Use runtime PM autosuspend feature, with 1s timeout, to avoid
> >> unnecessary suspend-resume cycles when, e.g. the userspace temporarily
> >> turns off the crtcs when configuring the outputs.
> >>
> >> Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
> >> ---
> >>   drivers/gpu/drm/tidss/tidss_drv.c | 8 +++++++-
> >>   1 file changed, 7 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/tidss/tidss_drv.c b/drivers/gpu/drm/tidss/tidss_drv.c
> >> index f403db11b846..64914331715a 100644
> >> --- a/drivers/gpu/drm/tidss/tidss_drv.c
> >> +++ b/drivers/gpu/drm/tidss/tidss_drv.c
> >> @@ -43,7 +43,9 @@ void tidss_runtime_put(struct tidss_device *tidss)
> >>   
> >>   	dev_dbg(tidss->dev, "%s\n", __func__);
> >>   
> >> -	r = pm_runtime_put_sync(tidss->dev);
> >> +	pm_runtime_mark_last_busy(tidss->dev);
> >> +
> >> +	r = pm_runtime_put_autosuspend(tidss->dev);
> >>   	WARN_ON(r < 0);
> >>   }
> >>   
> >> @@ -144,6 +146,9 @@ static int tidss_probe(struct platform_device *pdev)
> >>   
> >>   	pm_runtime_enable(dev);
> >>   
> >> +	pm_runtime_set_autosuspend_delay(dev, 1000);
> >> +	pm_runtime_use_autosuspend(dev);
> >> +
> >>   #ifndef CONFIG_PM
> >>   	/* If we don't have PM, we need to call resume manually */
> >>   	dispc_runtime_resume(tidss->dispc);
> > 
> > By the way, there's a way to handle this without any ifdef:
> > 
> > 	dispc_runtime_resume(tidss->dispc);
> > 
> > 	pm_runtime_set_active(dev);
> > 	pm_runtime_get_noresume(dev);
> > 	pm_runtime_enable(dev);
> > 	pm_runtime_set_autosuspend_delay(dev, 1000);
> > 	pm_runtime_use_autosuspend(dev);
> 
> I'm not sure I follow what you are trying to do here. The call to 
> dispc_runtime_resume() would crash if we have PM, as the HW would not be 
> enabled at that point.

Isn't dispc_runtime_resume() meant to enable the hardware ?

The idea is to enable the hardware, then enable runtime PM, and tell the
runtime PM framework that the device is enabled. If CONFIG_PM is not
set, the RPM calls will be no-ops, and the device will stay enable. If
CONFIG_PM is set, the device will be enabled, and will get disabled at
end of probe by a call to pm_runtime_put_autosuspend().

> And even if it wouldn't, we don't want to call dispc_runtime_resume()
> in probe when we have PM.

Don't you need to enable the device at probe time in order to reset it,
as done in later patches in the series ?

> > Then, in the error path,
> > 
> > 	pm_runtime_dont_use_autosuspend(dev);
> > 	pm_runtime_disable(dev);
> > 	pm_runtime_put_noidle(dev);
> > 
> > 	dispc_runtime_suspend(tidss->dispc);
> > 
> > And in remove:
> > 
> > 	pm_runtime_dont_use_autosuspend(dev);
> > 	pm_runtime_disable(dev);
> > 	if (!pm_runtime_status_suspended(dev))
> > 		dispc_runtime_suspend(tidss->dispc);
> > 	pm_runtime_set_suspended(dev);
> > 
> > And yes, runtime PM is a horrible API.
> > 
> >> @@ -215,6 +220,7 @@ static void tidss_remove(struct platform_device *pdev)
> >>   	/* If we don't have PM, we need to call suspend manually */
> >>   	dispc_runtime_suspend(tidss->dispc);
> >>   #endif
> >> +	pm_runtime_dont_use_autosuspend(dev);
> > 
> > This also needs to be done in the probe error path.
> 
> Oops. Right, I'll add that.

-- 
Regards,

Laurent Pinchart