On Fri, May 8, 2020 at 7:09 PM Rodrigo Vivi <[email protected]> wrote: > > On Fri, Apr 17, 2020 at 09:28:34PM +0300, Ville Syrjälä wrote: > > On Fri, Apr 17, 2020 at 08:10:26PM +0200, Daniel Vetter wrote: > > > On Fri, Apr 17, 2020 at 5:43 PM Ville Syrjälä > > > <[email protected]> wrote: > > > > > > > > On Fri, Apr 17, 2020 at 05:23:10PM +0200, Daniel Vetter wrote: > > > > > On Thu, Apr 16, 2020 at 08:04:20PM +0300, Ville Syrjala wrote: > > > > > > From: Ville Syrjälä <[email protected]> > > > > > > > > > > > > Revert back to comparing fb->format->format instead fb->format for > > > > > > the > > > > > > page flip ioctl. This check was originally only here to disallow > > > > > > pixel > > > > > > format changes, but when we changed it to do the pointer comparison > > > > > > we potentially started to reject some (but definitely not all) > > > > > > modifier > > > > > > changes as well. In fact the current behaviour depends on whether > > > > > > the > > > > > > driver overrides the format info for a specific format+modifier > > > > > > combo. > > > > > > Eg. on i915 this now rejects compression vs. no compression changes > > > > > > but > > > > > > does not reject any other tiling changes. That's just inconsistent > > > > > > nonsense. > > > > > > > > > > > > The main reason we have to go back to the old behaviour is to fix > > > > > > page > > > > > > flipping with Xorg. At some point Xorg got its atomic rights taken > > > > > > away > > > > > > and since then we can't page flip between compressed and > > > > > > non-compressed > > > > > > fbs on i915. Currently we get no page flipping for any games pretty > > > > > > much > > > > > > since Mesa likes to use compressed buffers. Not sure how > > > > > > compositors are > > > > > > working around this (don't use one myself). I guess they must be > > > > > > doing > > > > > > something to get non-compressed buffers instead. Either that or > > > > > > somehow no one noticed the tearing from the blit fallback. > > > > > > > > > > Mesa only uses compressed buffers if you enable modifiers, and > > > > > there's a > > > > > _loooooooooooot_ more that needs to be fixed in Xorg to enable that > > > > > for > > > > > real. Like real atomic support. > > > > > > > > Why would you need atomic for modifiers? Xorg doesn't even have > > > > any sensible framework for atomic and I suspect it never will. > > > > > > Frankly if no one cares about atomic in X I don't think we should do > > > work-arounds for lack of atomic in X. > > > > > > > > Without modifiers all you get is X tiling, > > > > > and that works just fine. > > > > > > > > > > Which would also fix this issue here you're papering over. > > > > > > > > > > So if this is the entire reason for this, I'm inclined to not do this. > > > > > Current Xorg is toast wrt modifiers, that's not news. > > > > > > > > Works just fine. Also pretty sure modifiers are even enabled by > > > > default now in modesetting. > > > > > > Y/CSS is harder to scan out, you need to verify with TEST_ONLY whether > > > it works. Otherwise good chances for some oddball black screens on > > > configurations that worked before. Which is why all non-atomic > > > compositors reverted modifiers by default again. > > > > Y alone is hard to scanout also, and yet we do nothing to reject that. > > It's just an inconsistent mess. > > > > If we really want to keep this check then we should rewrite it > > to be explicit: > > > > if (old_fb->format->format != new_fb->format->format || > > is_ccs(old_fb->modifier) != is_ccs(new_fb->modifier)) > > return -EINVAL; > > > > Now it's just a random thing that may even stop doing what it's > > currently doing if anyone touches their .get_format_info() > > implementation. > > > > > > > > > And as stated the current check doesn't have consistent behaviour > > > > anyway. You can still flip between different modifiers as long a the > > > > driver doesn't override .get_format_info() for one of them. The *only* > > > > case where that happens is CCS on i915. There is no valid reason to > > > > special case that one. > > > > > > The thing is, you need atomic to make CCS work reliably enough for > > > compositors and distros to dare enabling it by default. > > > > If it's not enabled by default then there is no harm in letting people > > explicitly enable it and get better performance. > > > > > CCS flipping > > > works with atomic. I really see no point in baking this in with as > > > uapi. > > > > It's just going back to the original intention of the check. > > Heck, the debug message doesn't even match what it's doing now. > > > > > Just fix Xorg. > > > > Be serious. No one is going to rewrite all the randr code to be atomic. > > I fully understand Daniel's concern here, but I also believe this won't be > done so soon at least. Meanwhile would it be acceptable to have a comment > with the code /* XXX: Xorg blah... */ or /* FIXME: After Xorg blah.. */ > ?
Here's a few numbers: - skl shipped in Aug 2015, so about 5 years. Since then would we like to have modifiers enabled for intel, because it costs us quite a bit of performance. This isn't new at all. - the last Xorg release is from May 2018, so two years. Meanwhile even patches to fix some of the atomic mixups in -modesetting landed, but they never shipped so not useful. - I spent a few hours (which really is nothing) reading Xorg code yesterday, and I concur with Daniel Stone's napkin estimate that this will take about half to one year to fix properly. It's not happening, no one is working on that. Conclusion: No one cares about modifiers on Xorg-modesetting. I don't see why the kernel should bend over for that. Once that has changed (I'm not betting on that) and there's clear effort behind modifiers for Xorg-modesetting I guess we can look into stop-gap measures, but meanwhile the best imo is to not disturb the dead. Cheers, Daniel > > > > > -Daniel > > > > > > > > > > > > -Daniel > > > > > > > > > > > > > > > > > Looking back at the original discussion on this change we pretty > > > > > > much > > > > > > just did it in the name of skipping a few extra pointer > > > > > > dereferences. > > > > > > However, I've decided not to revert the whole thing in case someone > > > > > > has since started to depend on these changes. None of the other > > > > > > checks > > > > > > are relevant for i915 anyways. > > > > > > > > > > > > Cc: [email protected] > > > > > > Cc: Laurent Pinchart <[email protected]> > > > > > > Fixes: dbd4d5761e1f ("drm: Replace 'format->format' comparisons to > > > > > > just 'format' comparisons") > > > > > > Signed-off-by: Ville Syrjälä <[email protected]> > > > > > > --- > > > > > > drivers/gpu/drm/drm_plane.c | 2 +- > > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/drivers/gpu/drm/drm_plane.c > > > > > > b/drivers/gpu/drm/drm_plane.c > > > > > > index d6ad60ab0d38..f2ca5315f23b 100644 > > > > > > --- a/drivers/gpu/drm/drm_plane.c > > > > > > +++ b/drivers/gpu/drm/drm_plane.c > > > > > > @@ -1153,7 +1153,7 @@ int drm_mode_page_flip_ioctl(struct > > > > > > drm_device *dev, > > > > > > if (ret) > > > > > > goto out; > > > > > > > > > > > > - if (old_fb->format != fb->format) { > > > > > > + if (old_fb->format->format != fb->format->format) { > > > > > > DRM_DEBUG_KMS("Page flip is not allowed to change frame > > > > > > buffer format.\n"); > > > > > > ret = -EINVAL; > > > > > > goto out; > > > > > > -- > > > > > > 2.24.1 > > > > > > > > > > > > _______________________________________________ > > > > > > dri-devel mailing list > > > > > > [email protected] > > > > > > https://lists.freedesktop.org/mailman/listinfo/dri-devel > > > > > > > > > > -- > > > > > Daniel Vetter > > > > > Software Engineer, Intel Corporation > > > > > http://blog.ffwll.ch > > > > > > > > -- > > > > Ville Syrjälä > > > > Intel > > > > > > > > > > > > -- > > > Daniel Vetter > > > Software Engineer, Intel Corporation > > > +41 (0) 79 365 57 48 - http://blog.ffwll.ch > > > > -- > > Ville Syrjälä > > Intel > > _______________________________________________ > > dri-devel mailing list > > [email protected] > > https://lists.freedesktop.org/mailman/listinfo/dri-devel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch _______________________________________________ Intel-gfx mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/intel-gfx
