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

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Date:   Thu, 2 Nov 2023 08:34:45 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To:     Laurent Pinchart <laurent.pinchart@...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
Subject: Re: [PATCH 02/10] drm/tidss: Use PM autosuspend

On 01/11/2023 15:54, Laurent Pinchart wrote:
> Hi Tomi,
> 
> Thank you for the patch.
> 
> 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. And even if it wouldn't, we don't want to call 
dispc_runtime_resume() in probe when we have PM.

> 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.

  Tomi