[PATCH v3] drm/ast: Don't check new mode if CRTC is being disabled

[dann frazier]

On Thu, May 07, 2020 at 11:06:40AM +0200, Thomas Zimmermann wrote:
> Suspending failed because there's no mode if the CRTC is being
> disabled. Early-out in this case. This fixes runtime PM for ast.
> 
> v3:
> 	* fixed commit message
> v2:
> 	* added Tested-by/Reported-by tags
> 	* added Fixes tags and CC (Sam)
> 	* improved comment
> 
> Signed-off-by: Thomas Zimmermann <tzimmermann at suse.de>
> Reported-by: Cary Garrett <cogarre at gmail.com>
> Tested-by: Cary Garrett <cogarre at gmail.com>
> Fixes: b48e1b6ffd28 ("drm/ast: Add CRTC helpers for atomic modesetting")
> Cc: Thomas Zimmermann <tzimmermann at suse.de>
> Cc: Gerd Hoffmann <kraxel at redhat.com>
> Cc: Dave Airlie <airlied at redhat.com>
> Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> Cc: Sam Ravnborg <sam at ravnborg.org>
> Cc: <stable at vger.kernel.org> # v5.6+
> ---
>  drivers/gpu/drm/ast/ast_mode.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index 7a9f20a2fd303..0cbbb21edb4e1 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -801,6 +801,9 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
>  		return -EINVAL;
>  	}
>  
> +	if (!state->enable)
> +		return 0; /* no mode checks if CRTC is being disabled */
> +
>  	ast_state = to_ast_crtc_state(state);
>  
>  	format = ast_state->format;

hey,
  I'm seeing a regression that I bisected down to this change. I
installed GNOME on a couple of different server models that have
AMI-based BMCs, which provide a web-based graphics display (virtual
KVM). When I enter the lock screen on current upstream kernels, the
display freezes, and I see the following messages appear in syslog
whenever I generate keyboard/mouse events on that display:

Jan 19 20:34:53 starbuck gnome-shell[5002]: Failed to post KMS update: drmModeAtomicCommit: Invalid argument
Jan 19 20:34:53 starbuck gnome-shell[5002]: Page flip discarded: drmModeAtomicCommit: Invalid argument
Jan 19 20:34:53 starbuck gnome-shell[5002]: Failed to post KMS update: drmModeAtomicCommit: Invalid argument
Jan 19 20:34:53 starbuck gnome-shell[5002]: Page flip discarded: drmModeAtomicCommit: Invalid argument
Jan 19 20:34:53 starbuck gnome-shell[5002]: Failed to post KMS update: drmModeAtomicCommit: Invalid argument
Jan 19 20:34:53 starbuck gnome-shell[5002]: Page flip discarded: drmModeAtomicCommit: Invalid argument
Jan 19 20:34:53 starbuck gnome-shell[5002]: Failed to post KMS update: drmModeAtomicCommit: Invalid argument

If I back out this change w/ the following patch (code has evolved
slightly preventing a clean revert), then the lock screen once again
behaves normally:

diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
index 956c8982192b..336c545c46f5 100644
--- a/drivers/gpu/drm/ast/ast_mode.c
+++ b/drivers/gpu/drm/ast/ast_mode.c
@@ -1012,9 +1012,6 @@ static int ast_crtc_helper_atomic_check(struct drm_crtc *crtc,
 	const struct drm_format_info *format;
 	bool succ;
 
-	if (!crtc_state->enable)
-		return 0; /* no mode checks if CRTC is being disabled */
-
 	ast_state = to_ast_crtc_state(crtc_state);
 
 	format = ast_state->format;


Apologies for noticing so long after the fact. I don't normally run a
desktop environment on these servers, I just happened to be debugging
something recently that required it.

  -dann