Re: [PATCH v2] drm/i915/fbdev: Enable late fbdev initial configuration

[Jani Nikula <jani.nikula@linux.intel.com>]

On Tue, 24 Apr 2018, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> Quoting José Roberto de Souza (2018-04-19 00:41:58)
>> If the initial fbdev configuration(intel_fbdev_initial_config()) runs and
>> there still no sink connected it will cause
>> drm_fb_helper_initial_config() to return 0 as no error happened(but
>> internally the return is -EAGAIN).
>> Because no framebuffer was allocated, when a sink is connected
>> intel_fbdev_output_poll_changed() will not execute
>> drm_fb_helper_hotplug_event() that would trigger another try to do the
>> initial fbdev configuration.
>> 
>> So here allowing drm_fb_helper_hotplug_event() to be executed when there
>> is not frambebuffer allocated and fbdev was not setup yet.
>> 
>> This issue also happens when a MST DP sink is connected since boot, as
>> the MST topology is discovered in parallel if intel_fbdev_initial_config()
>> is executed before the first sink MST is discovered it will cause this
>> same issue.
>> 
>> This is a follow up patch of
>> https://patchwork.freedesktop.org/patch/196089/
>> 
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104158
>> Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=104425
>> Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
>> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
>> Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
>> ---
>> 
>> Changes from v1:
>> - not creating a dump framebuffer anymore, instead just allowing
>> drm_fb_helper_hotplug_event() to execute when fbdev is not setup yet.
>> 
>>  drivers/gpu/drm/i915/intel_fbdev.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
>> index 7d41d139341b..e9e02b58b7be 100644
>> --- a/drivers/gpu/drm/i915/intel_fbdev.c
>> +++ b/drivers/gpu/drm/i915/intel_fbdev.c
>> @@ -807,7 +807,7 @@ void intel_fbdev_output_poll_changed(struct drm_device *dev)
>>                 return;
>>  
>>         intel_fbdev_sync(ifbdev);
>> -       if (ifbdev->vma)
>> +       if (ifbdev->vma || ifbdev->helper.deferred_setup)
>
> Feels slightly dodgy, vma can only be set and deferred_setup only be
> cleared at runtime, so at worst we may miss sending a hpd event during a
> runtime configuration phase. Which is probably just as well.
>
> What happens if we send two hpd events, and the first gets a deferred setup
> that fails. Do we hit the previous error condition? At least we are not
> hitting the condition of running the hotplug event while trying to do
> the initial configuration, but does the deferred setup have the same
> bugs?
>
>>                 drm_fb_helper_hotplug_event(&ifbdev->helper);
>
> I fear this is just poking the bear,
> Acked-by: Chris Wilson <chris@chris-wilson.co.uk>

Thanks for the patch and the ack. Pushed. If it's not a fix, at least it
papers over the regression for now...

BR,
Jani.



> -Chris
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-- 
Jani Nikula, Intel Open Source Technology Center
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