linux-kernel - Re: [PATCH 2/3] drm/panthor: Retry OPP transition to suspension state a few times

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Message-ID: <20241014092855.5c761b13@collabora.com>
Date: Mon, 14 Oct 2024 09:28:55 +0200
From: Boris Brezillon <boris.brezillon@...labora.com>
To: Adrián Larumbe <adrian.larumbe@...labora.com>
Cc: Steven Price <steven.price@....com>, Liviu Dudau <liviu.dudau@....com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
 <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
 <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, kernel@...labora.com,
 dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] drm/panthor: Retry OPP transition to suspension
 state a few times

On Fri, 11 Oct 2024 23:57:00 +0100
Adrián Larumbe <adrian.larumbe@...labora.com> wrote:

> When the device's runtime PM suspend callback is invoked, the switch to
> a suspension OPP might sometimes fail. Although this is beyond the
> control of the Panthor driver, we can attempt suspending it more than
> once as a defensive strategy.
> 
> Signed-off-by: Adrián Larumbe <adrian.larumbe@...labora.com>
> ---
>  drivers/gpu/drm/panthor/panthor_device.c | 8 +++++++-
>  1 file changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_device.c b/drivers/gpu/drm/panthor/panthor_device.c
> index cedd3cbcb47d..5430557bd0b8 100644
> --- a/drivers/gpu/drm/panthor/panthor_device.c
> +++ b/drivers/gpu/drm/panthor/panthor_device.c
> @@ -490,6 +490,7 @@ int panthor_device_resume(struct device *dev)
>  int panthor_device_suspend(struct device *dev)
>  {
>  	struct panthor_device *ptdev = dev_get_drvdata(dev);
> +	unsigned int susp_retries;
>  	int ret, cookie;
>  
>  	if (atomic_read(&ptdev->pm.state) != PANTHOR_DEVICE_PM_STATE_ACTIVE)
> @@ -522,7 +523,12 @@ int panthor_device_suspend(struct device *dev)
>  		drm_dev_exit(cookie);
>  	}
>  
> -	ret = panthor_devfreq_suspend(ptdev);
> +	for (susp_retries = 0; susp_retries < 5; susp_retries++) {
> +		ret = panthor_devfreq_suspend(ptdev);
> +		if (!ret)
> +			break;
> +	}

This retry logic should probably be moved to panthor_devfreq_suspend(),
but as Liviu said, I think we need to better understand why it takes
several attempts for an OPP transition to succeed.

> +
>  	if (ret) {
>  		if (panthor_device_is_initialized(ptdev) &&
>  		    drm_dev_enter(&ptdev->base, &cookie)) {