[RFC v2 1/8] drm/fb-helper: Add fb_deferred_io support

[Noralf Trønnes]

Den 20.04.2016 13:12, skrev Daniel Vetter:
> On Mon, Apr 18, 2016 at 05:15:03PM +0200, Noralf Trønnes wrote:
>> Den 13.04.2016 13:09, skrev Daniel Vetter:
>>> On Fri, Apr 08, 2016 at 07:05:03PM +0200, Noralf Trønnes wrote:
>>>> This adds deferred io support if CONFIG_FB_DEFERRED_IO is enabled.
>>>> Accumulated fbdev framebuffer changes are signaled using the callback
>>>> (struct drm_framebuffer_funcs *)->dirty()
>>>>
>>>> The drm_fb_helper_sys_*() functions will accumulate changes and
>>>> schedule fb_info.deferred_work _if_ fb_info.fbdefio is set.
>>>> This worker is used by the deferred io mmap code to signal that it
>>>> has been collecting page faults. The page faults and/or other changes
>>>> are then merged into a drm_clip_rect and passed to the framebuffer
>>>> dirty() function.
>>>>
>>>> The driver is responsible for setting up the fb_info.fbdefio structure
>>>> and calling fb_deferred_io_init() using the provided callback:
>>>> (struct fb_info *)->fbdefio->deferred_io = drm_fb_helper_deferred_io;
>>>>
>>>> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>
>>> For this one it'd be awesome to throw patches for qxl/udl on top to remove
>>> their own hand-rolled implementations. Just to maximize the testing
>>> coverage of this new code. Should be doable to set up a qxl virtual
>>> machine quickly, but even without that we should be able to pull it in
>>> (since it's mostly just about removing code from these two drivers).
>> There are three fb_deferred_io users in drivers/gpu/drm: qxl, udl and
>> vmwgfx.
>>
>> drivers/gpu/drm/vmwgfx
>> It doesn't use drm_fb_helper (uses the cfb_{fillrect,copyarea,imageblit}
>> functions directly). This made me think that I should probably add
>> fb_deferred_io support to drm_fb_helper_cfb_*() as well.
> Yup, that one is special and can be ignored.
>
>> drivers/gpu/drm/udl
>> First of all it has had deferred io disabled by default since 2013
>> (commit 677d23b). Secondly it handles damage directly in it's
>> fb_{fillrect,copyarea,imageblit} functions, but defers to the next call if
>> it is in atomic context. My patch always defers those function to a worker.
>> The driver uses the drm_fb_helper_sys_* functions, so my patch would mess
>> it up if someone would enable deferred io (module_param: fb_defio).
>> So this driver isn't a good candidate for easy conversion also because it
>> has different code paths for fbdev mmap damage and the other damages
>> (although the code is similar). But it needs a patch to use the sys_*()
>> functions directly.
> Since it's disabled by default I'd just do a conversion. It should result
> largely in deleting code and just using the fb helpers. What's special
> with the mmap handling, and do we care?

The git log mentions page list corruption, but I realised that I can
just disable the deferred mmap code and keep the rest.