[PATCH] drm/dp: Do not prune the last mode on the connector

[PATCH] drm/dp: Do not prune the last mode on the connector

[Manasi Navare]

Currently the drm_mode_prune_invalid() function will
prune all the modes if it finds that the mode-status
is not MODE_OK. But if it ends up pruning all modes
then there are no modes left for that connector which will
eventually result into a black screen as userspace sees no
modes from the kernel. This can happen pretty quickly in case of
eDP panel that has only mode that might get pruned.
This patch fixes this problem by checking if the mode being pruned
is the last mode on that connector and if so doesnt prune it.

Cc: dri-devel@lists.freedesktop.org
Cc: Keith Packard <keithp@keithp.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
---
 drivers/gpu/drm/drm_modes.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index 4a3f68a..a9369eb 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1185,7 +1185,8 @@ void drm_mode_prune_invalid(struct drm_device *dev,
 	struct drm_display_mode *mode, *t;
 
 	list_for_each_entry_safe(mode, t, mode_list, head) {
-		if (mode->status != MODE_OK) {
+		if (mode->status != MODE_OK &&
+		    !(list_is_last(&mode->head, mode_list))) {
 			list_del(&mode->head);
 			if (verbose) {
 				drm_mode_debug_printmodeline(mode);
-- 
2.1.4

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Re: [PATCH] drm/dp: Do not prune the last mode on the connector

[Keith Packard]

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Manasi Navare <manasi.d.navare@intel.com> writes:

> This patch fixes this problem by checking if the mode being pruned
> is the last mode on that connector and if so doesnt prune it.

I think you want to stop pruning when you've gotten to a single mode on
the list, not at the last mode in the list (which may well need to be
pruned).

This is entirely untested, but perhaps

+		    !(list_is_singular(mode_list))) {
        
is what you want?

-- 
-keith

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Re: [PATCH] drm/dp: Do not prune the last mode on the connector

[Manasi Navare]

On Wed, Sep 27, 2017 at 05:31:56PM -0700, Keith Packard wrote:
> Manasi Navare <manasi.d.navare@intel.com> writes:
> 
> > This patch fixes this problem by checking if the mode being pruned
> > is the last mode on that connector and if so doesnt prune it.
> 
> I think you want to stop pruning when you've gotten to a single mode on
> the list, not at the last mode in the list (which may well need to be
> pruned).
> 
> This is entirely untested, but perhaps
> 
> +		    !(list_is_singular(mode_list))) {
>         
> is what you want?
>

Thanks Keith. Yes thats correct, I got confused by the macro name.
But its correct I should use the list_is_singular instead.

Manasi
 
> -- 
> -keith


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[PATCH v2] drm/dp: Do not prune the last mode on the connector

[Manasi Navare]

Currently the drm_mode_prune_invalid() function will
prune all the modes if it finds that the mode-status
is not MODE_OK. But if it ends up pruning all modes
then there are no modes left for that connector which will
eventually result into a black screen as userspace sees no
modes from the kernel. This can happen pretty quickly in case of
eDP panel that has only mode that might get pruned.
This patch fixes this problem by checking if the mode being pruned
is the last mode(only mode) on that connector and if so doesnt prune it.

v2:
* Use correct macro from list.h (Keith Packard)

Cc: dri-devel@lists.freedesktop.org
Cc: Keith Packard <keithp@keithp.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: Ville Syrjala <ville.syrjala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
---
 drivers/gpu/drm/drm_modes.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
index 4a3f68a..9dc38a4 100644
--- a/drivers/gpu/drm/drm_modes.c
+++ b/drivers/gpu/drm/drm_modes.c
@@ -1185,7 +1185,8 @@ void drm_mode_prune_invalid(struct drm_device *dev,
 	struct drm_display_mode *mode, *t;
 
 	list_for_each_entry_safe(mode, t, mode_list, head) {
-		if (mode->status != MODE_OK) {
+		if (mode->status != MODE_OK &&
+		    !list_is_singular(mode_list)) {
 			list_del(&mode->head);
 			if (verbose) {
 				drm_mode_debug_printmodeline(mode);
-- 
2.1.4

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