linux-kernel - Re: [PATCH 3/5] drm/amd: fix fb references in async update

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Message-ID: <e421e3c9-abb0-5763-1aa0-1e21e0abd09f@amd.com>
Date:   Mon, 4 Mar 2019 15:51:44 +0000
From:   "Kazlauskas, Nicholas" <Nicholas.Kazlauskas@....com>
To:     Helen Koike <helen.koike@...labora.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
CC:     Stéphane Marchesin <marcheu@...gle.com>,
        Sean Paul <seanpaul@...gle.com>,
        David Airlie <airlied@...ux.ie>,
        "daniel.vetter@...ll.ch" <daniel.vetter@...ll.ch>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Tomasz Figa <tfiga@...omium.org>,
        "boris.brezillon@...labora.com" <boris.brezillon@...labora.com>,
        "kernel@...labora.com" <kernel@...labora.com>
Subject: Re: [PATCH 3/5] drm/amd: fix fb references in async update

On 3/4/19 9:49 AM, Helen Koike wrote:
> Async update callbacks are expected to set the old_fb in the new_state
> so prepare/cleanup framebuffers are balanced.
> 
> Calling drm_atomic_set_fb_for_plane() (which gets a reference of the new
> fb and put the old fb) is not required, as it's taken care by
> drm_mode_cursor_universal() when calling drm_atomic_helper_update_plane().
> 
> Suggested-by: Boris Brezillon <boris.brezillon@...labora.com>
> Signed-off-by: Helen Koike <helen.koike@...labora.com>

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@....com>

I guess the swap itself should be enough here as per the commit description.

It would have been nice if this patch dropped the old_plane_state->fb != 
new_plane_state->fb check too at the same time, but I suppose I can drop 
that later. It'll help us pass those failing IGT tests as well.

Nicholas Kazlauskas


> 
> ---
> Hello,
> 
> As mentioned in the cover letter,
> I tested on the rockchip and on i915 using igt plane_cursor_legacy and
> kms_cursor_legacy and I didn't see any regressions.
> But I couldn't test on AMD because I don't have the hardware and I would
> appreciate if anyone could test it.
> 
> Also, I didn't CC to stable here as I saw the async_update function was only
> added on v4.20, please let me know if I should CC to stable.
> 
> Thanks!
> Helen
> 
>   drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> index 3a6f595f295e..bc02800254bf 100644
> --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> @@ -3760,8 +3760,7 @@ static void dm_plane_atomic_async_update(struct drm_plane *plane,
>   	struct drm_plane_state *old_state =
>   		drm_atomic_get_old_plane_state(new_state->state, plane);
>   
> -	if (plane->state->fb != new_state->fb)
> -		drm_atomic_set_fb_for_plane(plane->state, new_state->fb);
> +	swap(plane->state->fb, new_state->fb);
>   
>   	plane->state->src_x = new_state->src_x;
>   	plane->state->src_y = new_state->src_y;
>