linux-kernel - Re: [PATCH v2] virtgpu: don't reset on shutdown

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Message-ID: <d6315206-6ef5-4c44-8450-85aac01946c9@suse.de>
Date: Thu, 17 Apr 2025 09:07:34 +0200
From: Thomas Zimmermann <tzimmermann@...e.de>
To: Gerd Hoffmann <kraxel@...hat.com>, "Michael S. Tsirkin" <mst@...hat.com>
Cc: linux-kernel@...r.kernel.org, Eric Auger <eric.auger@...hat.com>,
 Eric Auger <eauger@...hat.com>, Jocelyn Falempe <jfalempe@...hat.com>,
 David Airlie <airlied@...hat.com>,
 Gurchetan Singh <gurchetansingh@...omium.org>, Chia-I Wu
 <olvaffe@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Simona Vetter <simona@...ll.ch>,
 Jason Wang <jasowang@...hat.com>, Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
 Eugenio Pérez <eperezma@...hat.com>,
 dri-devel@...ts.freedesktop.org, virtualization@...ts.linux.dev
Subject: Re: [PATCH v2] virtgpu: don't reset on shutdown

Hi

Am 16.04.25 um 15:57 schrieb Gerd Hoffmann:
> On Tue, Apr 15, 2025 at 10:00:48AM -0400, Michael S. Tsirkin wrote:
>> On Tue, Apr 15, 2025 at 01:16:32PM +0200, Gerd Hoffmann wrote:
>>>    Hi,
>>>
>>>> +static void virtio_gpu_shutdown(struct virtio_device *vdev)
>>>> +{
>>>> +	/*
>>>> +	 * drm does its own synchronization on shutdown.
>>>> +	 * Do nothing here, opt out of device reset.
>>>> +	 */
>>> I think a call to 'drm_dev_unplug()' is what you need here.
>>>
>>> take care,
>>>    Gerd
>> My patch reverts the behaviour back to what it was, so pls go
>> ahead and send a patch on top? I won't be able to explain
>> what it does and why it's needed.
> See below.  Untested.
>
> Eric, can you give this a spin?
>
> thanks,
>    Gerd
>
> ----------------------- cut here -------------------------------
>  From f3051dd52cb2004232941e6d2cbc0c694e290534 Mon Sep 17 00:00:00 2001
> From: Gerd Hoffmann <kraxel@...hat.com>
> Date: Wed, 16 Apr 2025 15:53:04 +0200
> Subject: [PATCH] drm/virtio: implement virtio_gpu_shutdown
>
> Calling drm_dev_unplug() is the drm way to say the device
> is gone and can not be accessed any more.
>
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
>   drivers/gpu/drm/virtio/virtgpu_drv.c | 8 ++++----
>   1 file changed, 4 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_drv.c b/drivers/gpu/drm/virtio/virtgpu_drv.c
> index e32e680c7197..71c6ccad4b99 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_drv.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_drv.c
> @@ -130,10 +130,10 @@ static void virtio_gpu_remove(struct virtio_device *vdev)
>   
>   static void virtio_gpu_shutdown(struct virtio_device *vdev)
>   {
> -	/*
> -	 * drm does its own synchronization on shutdown.
> -	 * Do nothing here, opt out of device reset.
> -	 */
> +	struct drm_device *dev = vdev->priv;
> +
> +	/* stop talking to the device */
> +	drm_dev_unplug(dev);
>   }

It's the correct approach but also requires drm_dev_enter() and 
drm_dev_exit() around all of the driver's hardware access.

Best regards
Thomas

>   
>   static void virtio_gpu_config_changed(struct virtio_device *vdev)

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)