Re: [PATCH v2 5/5] drm/i915: Bump gen4+ fb size limits to 32kx32k

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Thu, Sep 20, 2018 at 08:46:42PM +0100, Chris Wilson wrote:
> Quoting Ville Syrjälä (2018-09-20 20:41:30)
> > On Thu, Sep 20, 2018 at 09:09:03AM +0100, Chris Wilson wrote:
> > > Quoting Ville Syrjälä (2018-09-19 17:59:51)
> > > > On Thu, Sep 13, 2018 at 11:01:40PM +0300, Ville Syrjala wrote:
> > > > > From: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > > 
> > > > > With gtt remapping in place we can use arbitraily large framebuffers.
> > > > > Let's bump the limits as high as we can (32k-1). Going beyond that
> > > > > would require switching our s16.16 src coordinate representation to
> > > > > something with more spare bits.
> > > > > 
> > > > > Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > > > > ---
> > > > >  drivers/gpu/drm/i915/intel_display.c | 4 ++--
> > > > >  1 file changed, 2 insertions(+), 2 deletions(-)
> > > > > 
> > > > > diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
> > > > > index 346572cf734a..0ee6255cd040 100644
> > > > > --- a/drivers/gpu/drm/i915/intel_display.c
> > > > > +++ b/drivers/gpu/drm/i915/intel_display.c
> > > > > @@ -15527,8 +15527,8 @@ int intel_modeset_init(struct drm_device *dev)
> > > > >               dev->mode_config.max_width = 4096;
> > > > >               dev->mode_config.max_height = 4096;
> > > > >       } else {
> > > > > -             dev->mode_config.max_width = 8192;
> > > > > -             dev->mode_config.max_height = 8192;
> > > > > +             dev->mode_config.max_width = 32767;
> > > > > +             dev->mode_config.max_height = 32767;
> > > > 
> > > > It appears that neither Mesa nor glamor will check whether window system
> > > > buffers exceed the capabilities of the 3D engine. So trying to use a >16k
> > > > trips an assert when genxml tries to pack the surface_state.
> > > > 
> > > > So looks like we'll need to limit this to 16k for gen7+, and leave it
> > > > at 8k for gen4+. If userspace gets smarter later on we could add a new
> > > > client cap to expose higher limits.
> > > 
> > > At which point, the client can just ignore this field and just use
> > > rejection criteria from addfb2 and/or setcrtc (or the atomic variant).
> > 
> > I suppose. Though probing the max size using addfb might be a bit
> > tedious. That's assuming the client wants to report the max in some
> > way, as X does.
> > 
> > > 
> > > Or we can just keep this field as meaning the maximum size of a single
> > > CRTC and just ignore it entirely in -modesetting for fb size as we do
> > > elsewhere.
> > 
> > Would require changing the core addfb code to ignore these
> > limits for i915 but keep chekcing them for the other drivers.
> > So a bit of work, and I'm not really sure what the actual
> > benefit for i915 would be.
> 
> Why is the core addfb using these fields? Since when did they *stop*
> being per-CRTC limits?

Looks like addfb has been using them since the beginning:

commit f453ba0460742ad027ae0c4c7d61e62817b3e7ef
Author: Dave Airlie <airlied@redhat.com>
Date:   Fri Nov 7 14:05:41 2008 -0800

    DRM: add mode setting support

And looks like they never matched the per-crtc limits for i915 either.
Until HSW hdisplay limit was 4k but max_width was already set to 8k
in:

commit 79e539453b34e35f39299a899d263b0a1f1670bd
Author: Jesse Barnes <jbarnes@virtuousgeek.org>
Date:   Fri Nov 7 14:24:08 2008 -0800

    DRM: i915: add mode setting support

-- 
Ville Syrjälä
Intel
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