Re: [PATCH v2 0/2] Fixes for omapdrm console

[Tony Lindgren <tony@atomide.com>]

* Thomas Zimmermann <tzimmermann@suse.de> [240227 07:56]:
> Am 27.02.24 um 08:06 schrieb Tony Lindgren:
> > * Tony Lindgren <tony@atomide.com> [240226 13:26]:
> > > * Thomas Zimmermann <tzimmermann@suse.de> [240226 09:10]:
> > > > Am 26.02.24 um 10:01 schrieb Tomi Valkeinen:
> > > > > On 26/02/2024 10:26, Tomi Valkeinen wrote:
> > > > > > How is it broken? I don't usually use the console (or fbdev) but
> > > > > > enabling it now, it seems to work fine for me, on DRA76 EVM with
> > > > > > HDMI output.
> > > > Omapdrm implements drm_framebuffer_funcs.dirty withomap_framebuffer_dirty().
> > > > AFAIK DRM semantics requires to run the dirty helper after writing to the
> > > > framebuffer's memory. Userspace does this via the DIRTYFB ioctl. [1] But (at
> > > > least) for correctness the console needs to do the same.
> > > > 
> > > > [1] https://elixir.bootlin.com/linux/v6.7.6/source/drivers/gpu/drm/drm_ioctl.c#L679
> > > Yes I noticed console not updating and bisected it down to the two
> > > commits listed. I did the bisect on a droid4 though with command mode
> > > LCD. I did not test with HDMI, will give that a try too.
> > I can reproduce the cache issue with Tomi's omapfb-tests [2] below:
> > 
> > while true;
> >        do dd if=/dev/urandom of=/dev/fb0
> >        ~/src/omapfb-tests/test
> >        sleep 1
> > done
> > 
> > That produces short random data stripes on the test image.
> > 
> > > > > After applying your patches, I see a lot of cache-related artifacts on
> > > > > the screen when updating the fb.
> > > > I guess we might need a dma-specific mmap helper to make this work
> > > > correctly.
> > Comparing the difference between drm_gem_mmap_obj() and
> > fb_deferred_io_mmap(), the following test patch makes the cache issue
> > go away for me. Not sure if this can be set based on some flag, or if
> > we need a separate fb_deferred_io_wc_mmap() or something like that?
> > 
> > [2] https://github.com/tomba/omapfb-tests
> > 
> > 8< --------------------
> > diff --git a/drivers/video/fbdev/core/fb_defio.c b/drivers/video/fbdev/core/fb_defio.c
> > --- a/drivers/video/fbdev/core/fb_defio.c
> > +++ b/drivers/video/fbdev/core/fb_defio.c
> > @@ -224,6 +224,7 @@ static const struct address_space_operations fb_deferred_io_aops = {
> >   int fb_deferred_io_mmap(struct fb_info *info, struct vm_area_struct *vma)
> >   {
> >   	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
> > +	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));
> 
> Great, that's exactly what I had in mind!

OK :)

> My proposal is to add this mmap function directly to omapdrm. I'll later
> take care of integrating this into the overall framework. I have a few other
> ideas in mind that are related to this issue. Ok?

OK that sounds good to me, I'll post v3 set of patches.

Regards,

Tony