[PATCH 4.19 regression fix 2/2] staging: vboxvideo: Change address of scanout buffer on page-flip

[Steve Longerbeam]

Hi Hans,


On 09/10/2018 11:30 AM, Hans de Goede wrote:
> Commit 2408898e3b6c ("staging: vboxvideo: Add page-flip support") only
> calls vbox_crtc_do_set_base() on page-flips, but despite that function's
> name it only pins the new fb, unpins the old fb and sets
> vbox_crtc->fb_offset. It does not program the hardware to scan out at the
> new vbox_crtc->fb_offset value.

Has that always been the case of vbox_crtc_do_set_base()? Or was
there a recent commit that changed that behavior?

I tested this patch using a Weston EGL mock navigation test app around
4.14 time-frame, that exercises page flip and it was scanning out the
new fb, but maybe what I was looking at was a scan-out of an old/now stale
fb from a previous page-flip.

In any case thanks for fixing.

Steve

> This was causing only every other frame (assuming page-flipping between 2
> buffers) to be shown since we kept scanning out of the old (now unpinned!)
> buffer.
>
> This commit fixes this by adding code to vbox_crtc_page_flip() to tell
> the hardware to scanout from the new fb_offset.
>
> Fixes: 2408898e3b6c ("staging: vboxvideo: Add page-flip support")
> Cc: Steve Longerbeam <steve_longerbeam at mentor.com>
> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
> ---
>   drivers/staging/vboxvideo/vbox_mode.c | 5 +++++
>   1 file changed, 5 insertions(+)
>
> diff --git a/drivers/staging/vboxvideo/vbox_mode.c b/drivers/staging/vboxvideo/vbox_mode.c
> index a83eac8668d0..79836c8fb909 100644
> --- a/drivers/staging/vboxvideo/vbox_mode.c
> +++ b/drivers/staging/vboxvideo/vbox_mode.c
> @@ -323,6 +323,11 @@ static int vbox_crtc_page_flip(struct drm_crtc *crtc,
>   	if (rc)
>   		return rc;
>   
> +	mutex_lock(&vbox->hw_mutex);
> +	vbox_set_view(crtc);
> +	vbox_do_modeset(crtc, &crtc->mode);
> +	mutex_unlock(&vbox->hw_mutex);
> +
>   	spin_lock_irqsave(&drm->event_lock, flags);
>   
>   	if (event)