Re: [PATCH RESEND v2 06/25] drm/fb_helper: Create a wrapper for remove_conflicting_framebuffers

[Archit Taneja <architt@codeaurora.org>]

On 07/29/2015 12:16 AM, Daniel Vetter wrote:
> On Wed, Jul 22, 2015 at 02:58:01PM +0530, Archit Taneja wrote:
>> Some drm drivers call remove_conflicting_framebuffers. Create a
>> drm_fb_helper function that wraps around these calls.
>>
>> This is part of an effort to prevent drm drivers from calling fbdev
>> functions directly, in order to make fbdev emulation a top level drm
>> option.
>>
>> v2:
>> - Added kerneldocs
>> - Follow the drm way of aligning of arguments in func definitions
>>
>> Signed-off-by: Archit Taneja <architt@codeaurora.org>
>> ---
>>   drivers/gpu/drm/drm_fb_helper.c | 15 +++++++++++++++
>>   include/drm/drm_fb_helper.h     |  4 ++++
>>   2 files changed, 19 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
>> index 9620aa5..86e4e2c 100644
>> --- a/drivers/gpu/drm/drm_fb_helper.c
>> +++ b/drivers/gpu/drm/drm_fb_helper.c
>> @@ -894,6 +894,21 @@ void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, int state)
>>   }
>>   EXPORT_SYMBOL(drm_fb_helper_set_suspend);
>>
>> +/**
>> + * drm_fb_helper_remove_conflicting_framebuffers - wrapper around
>> + *						remove_conflicting_framebuffers
>> + * @fb_helper: driver-allocated fbdev helper
>> + *
>> + * A wrapper around remove_conflicting_framebuffers implemented by fbdev core
>> + */
>> +int drm_fb_helper_remove_conflicting_framebuffers(struct apertures_struct *a,
>> +						  const char *name,
>> +						  bool primary)
>> +{
>> +	return remove_conflicting_framebuffers(a, name, primary);
>> +}
>> +EXPORT_SYMBOL(drm_fb_helper_remove_conflicting_framebuffers);
>
> Chris Wilson reported on irc that if he builds with I915_FBDEV=n then
> there's a missing symbol problem here because i915 wants to kick out other
> framebuffers (well we have to for correctness) even when fbdev emulation
> is disabled. If you look at i915_dma.c you'll see that the call to
> remove_conflicting_framebuffers is conditional upon CONFIG_FB and not
> CONFIG_I915_FBDEV.
>
> I think the proper solution here would be to provide a static inline
> helper for remove_conflicting_framebuffer itself when CONFIG_FB=n, since a
> all drivers who call this still want to call this even when fbdev
> emulation is disabled.
>
> Plan B would be to move this into core drm and make the static inline one
> selected for CONFIG_FB=n. If you do that then maybe also rename it to
> drm_remove_conflicting_framebuffer since this really is only tangetial to
> fbdev emulation.

The remove_conflicting_framebuffers calls do_unregister_framebuffer(),
which seems to be quite central to fb core, and can't just work without
other fb core funcs.

What I don't get is, if legacy fb was never enabled, how did we end up
registering fbs in the first place?

Could you briefly explain what these other 'framebuffers' are that
remove_conflicting_framebuffers removes? The comments say that they are
firmware allocated fbs. I'm not well versed with what happens in
desktop graphics.

Archit

>
> Anyway current patch unfortunately won't work since we really must remove
> other framebuffers even in the FB=y, I915_FBDEV=n case. So I dropped it
> from drm-misc for now. Unfortunately that means all the driver conversions
> won't apply anymore either :(
>
> Thanks, Daniel
>> +
>>   static int setcolreg(struct drm_crtc *crtc, u16 red, u16 green,
>>   		     u16 blue, u16 regno, struct fb_info *info)
>>   {
>> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
>> index ef32500..cbdc69d 100644
>> --- a/include/drm/drm_fb_helper.h
>> +++ b/include/drm/drm_fb_helper.h
>> @@ -168,6 +168,10 @@ void drm_fb_helper_cfb_imageblit(struct fb_info *info,
>>
>>   void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, int state);
>>
>> +int drm_fb_helper_remove_conflicting_framebuffers(struct apertures_struct *a,
>> +						  const char *name,
>> +						  bool primary);
>> +
>>   int drm_fb_helper_setcmap(struct fb_cmap *cmap, struct fb_info *info);
>>
>>   int drm_fb_helper_hotplug_event(struct drm_fb_helper *fb_helper);
>> --
>> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
>> hosted by The Linux Foundation
>>
>

-- 
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum,
a Linux Foundation Collaborative Project
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