On Fri, Oct 30, 2020 at 02:19:45PM +0000, Chris Wilson wrote: > Quoting Ville Syrjala (2020-10-22 20:42:56) > > From: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > > > The new >8k CEA modes have dotclocks reaching 5.94 GHz, which > > means our clock*1000 will now overflow the 32bit unsigned > > integer. Switch to 64bit maths to avoid it. > > > > Cc: stable@xxxxxxxxxxxxxxx > > Reported-by: Randy Dunlap <rdunlap@xxxxxxxxxxxxx> > > Signed-off-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> > > --- > > An interesting question how many other place might suffer from similar > > overflows. I think i915 should be mostly OK. The one place I know we use > > Hz instead kHz is the hsw DPLL code, which I would prefer we also change > > to use kHz. The other concern is whether we have any potential overflows > > before we check this against the platform's max dotclock. > > > > I do have this unreviewed igt series > > https://patchwork.freedesktop.org/series/69531/ which extends the > > current testing with some other forms of invalid modes. Could probably > > extend that with a mode.clock=INT_MAX test to see if anything else might > > trip up. > > > > No idea about other drivers. > > > > drivers/gpu/drm/drm_modes.c | 4 ++-- > > 1 file changed, 2 insertions(+), 2 deletions(-) > > > > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c > > index 501b4fe55a3d..511cde5c7fa6 100644 > > --- a/drivers/gpu/drm/drm_modes.c > > +++ b/drivers/gpu/drm/drm_modes.c > > @@ -762,7 +762,7 @@ int drm_mode_vrefresh(const struct drm_display_mode *mode) > > if (mode->htotal == 0 || mode->vtotal == 0) > > return 0; > > > > - num = mode->clock * 1000; > > + num = mode->clock; > > den = mode->htotal * mode->vtotal; > > You don't want to promote den to u64 while you are here? We are at > 8kx4k, throw in dblscan and some vscan, and we could soon have wacky > refresh rates. i915 has 16kx8k hard limit currently, and we reject vscan>1 (wish we could also reject DBLSCAN). So we should not hit that, at least not yet. Other drivers might not be so strict I guess. I have a nagging feeling that other places are in danger of overflows if we try to push the current limits significantly. But I guess no real harm in going full 64bit here, except maybe making it a bit slower. -- Ville Syrjälä Intel
