linux-kernel - Re: [PATCH v3 2/4] drm/qxl: unpin release objects

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Date:   Fri, 22 Jan 2021 09:13:42 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Gerd Hoffmann <kraxel@...hat.com>, dri-devel@...ts.freedesktop.org
Cc:     David Airlie <airlied@...ux.ie>,
        open list <linux-kernel@...r.kernel.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <virtualization@...ts.linux-foundation.org>,
        "open list:DRM DRIVER FOR QXL VIRTUAL GPU" 
        <spice-devel@...ts.freedesktop.org>,
        Dave Airlie <airlied@...hat.com>
Subject: Re: [PATCH v3 2/4] drm/qxl: unpin release objects

Hi

Am 20.01.21 um 12:12 schrieb Gerd Hoffmann:
> Balances the qxl_create_bo(..., pinned=true, ...);
> call in qxl_release_bo_alloc().
> 
> Signed-off-by: Gerd Hoffmann <kraxel@...hat.com>
> ---
>   drivers/gpu/drm/qxl/qxl_release.c | 1 +
>   1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/gpu/drm/qxl/qxl_release.c b/drivers/gpu/drm/qxl/qxl_release.c
> index 0fcfc952d5e9..add979cba11b 100644
> --- a/drivers/gpu/drm/qxl/qxl_release.c
> +++ b/drivers/gpu/drm/qxl/qxl_release.c
> @@ -166,6 +166,7 @@ qxl_release_free_list(struct qxl_release *release)
>   		entry = container_of(release->bos.next,
>   				     struct qxl_bo_list, tv.head);
>   		bo = to_qxl_bo(entry->tv.bo);
> +		bo->tbo.pin_count = 0; /* ttm_bo_unpin(&bo->tbo); */

This code looks like a workaround or a bug.

AFAICT the only place with pre-pinned BO is qdev->dumb_shadow_bo. Can 
you remove the pinned flag entirely and handle pinning as part of 
dumb_shadow_bo's code.

Otherwise maybe use

if (pin_count)
     ttm_bo_unpin();
WARN_ON(pin_count); /* should always be 0 now */

with a comment similar to the commit's description.

Best regards
Thomas

>   		qxl_bo_unref(&bo);
>   		list_del(&entry->tv.head);
>   		kfree(entry);
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer



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