Hi
On Wed, Nov 27, 2013 at 9:24 PM, Paulo Zanoni przanoni@gmail.com wrote:
From: Paulo Zanoni paulo.r.zanoni@intel.com
Sometimes we want to disable all the screens on a system, because that will allow the graphics card to be put into low-power states. The problem is that, for example, while all screens are disabled, if we get a hotplug interrupt, fbcon will decide to set a mode instead of keeping everything disabled, which will remove us from our low power states.
Let's assume that if there's a DRM master, it will be able to do whatever is appropriate when we get the hotplug.
This problem can be reproduced by the runtime PM test program from intel-gpu-tools: we disable all the screens so the graphics device can be put into D3, then something triggers a hotplug interrupt, fbcon sets a mode and breaks our test suite. The problem can be reproduced more easily by the "i2c" subtest.
Other approaches considered for the problem: - Return "false" if "bound == 0" and the caller of drm_fb_helper_is_bound is a hotplug handler. This would break the case where the machine boots with no outputs connected, then the user plugs a monitor. - Add a new IOCTL to force fbcon to not set modes. This would keep all the current applications behaving the same, but adding a new IOCTL is not always the greatest idea. - Return false only if "dev->primary->master && bound == 0". This was my first implementation, but Chris suggested we should do the check irrespective of the "bound" variable.
Thanks to Daniel Vetter for the investigation, ideas and the implementation of the hotplug alternative.
v2: - Do the check first, irrespective of "bound". - Cc dri-devel
Thank god all that will get dropped with CONFIG_FB=n. Anyhow:
Reviewed-by: David Herrmann dh.herrmann@gmail.com
Thanks David
Cc: dri-devel@lists.freedesktop.org Credits-to: Daniel Vetter daniel.vetter@ffwll.ch Signed-off-by: Paulo Zanoni paulo.r.zanoni@intel.com
drivers/gpu/drm/drm_fb_helper.c | 6 ++++++ 1 file changed, 6 insertions(+)
diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index 0a19401..98a0363 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -359,6 +359,11 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper) struct drm_crtc *crtc; int bound = 0, crtcs_bound = 0;
/* Sometimes user space wants everything disabled, so don't steal the* display if there's a master. */if (dev->primary->master)return false;list_for_each_entry(crtc, &dev->mode_config.crtc_list, head) { if (crtc->fb) crtcs_bound++;@@ -368,6 +373,7 @@ static bool drm_fb_helper_is_bound(struct drm_fb_helper *fb_helper)
if (bound < crtcs_bound) return false;
return true;}
-- 1.8.3.1
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