On Tue, 2014-09-30 at 10:04 +0200, Daniel Vetter wrote: > On Mon, Sep 29, 2014 at 03:49:32PM -0700, U. Artie Eoff wrote: > > Improper truncated integer division in the scale() function causes > > actual_brightness != brightness. This (partial) work-around should be > > sufficient for a majority of use-cases, but it is by no means a complete > > solution. > > > > TODO: Determine how best to scale "user" values to "hw" values, and > > vice-versa, when the ranges are of different sizes. That would be a > > buggy scenario even with this work-around. > > > > The issue was introduced in the following (v3.17-rc1) commit: > > > > 6dda730 drm/i915: respect the VBT minimum backlight brightness > > > > v2: (thanks to Chris Wilson) clarify commit message, use rounded division > > macro > > > > v3: -DIV_ROUND_CLOSEST() fails to build with CONFIG_X86_32=y. (Jani) > > -Use DIV_ROUND_CLOSEST_ULL() instead. (Damien) > > -v1 and v2 originally authored by Joe Konno. > > > > Signed-off-by: U. Artie Eoff <ullysses.a.e...@intel.com> > > Is there some bug report, internal jira, mailing list reference or similar > about this? > > Note that at least for OTC jira tasks we now want them to be added to > commit message with e.g. > > OTC-Jria: VIZ-4932 >
Yes, the OTC-Jira task is: VIZ-4395. I'll resubmit with amended commit message. > And I guess I should merge patch 2 before patch 1, right? No, patch 1 before patch 2. Thanks, --U. Artie > > Cheers, Daniel > > > --- > > drivers/gpu/drm/i915/intel_panel.c | 8 +++++--- > > 1 file changed, 5 insertions(+), 3 deletions(-) > > > > diff --git a/drivers/gpu/drm/i915/intel_panel.c > > b/drivers/gpu/drm/i915/intel_panel.c > > index f17ada3..f7da913 100644 > > --- a/drivers/gpu/drm/i915/intel_panel.c > > +++ b/drivers/gpu/drm/i915/intel_panel.c > > @@ -398,6 +398,9 @@ intel_panel_detect(struct drm_device *dev) > > } > > } > > > > +#define DIV_ROUND_CLOSEST_ULL(ll, d) \ > > +({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; }) > > + > > /** > > * scale - scale values from one range to another > > * > > @@ -419,9 +422,8 @@ static uint32_t scale(uint32_t source_val, > > source_val = clamp(source_val, source_min, source_max); > > > > /* avoid overflows */ > > - target_val = (uint64_t)(source_val - source_min) * > > - (target_max - target_min); > > - do_div(target_val, source_max - source_min); > > + target_val = DIV_ROUND_CLOSEST_ULL((uint64_t)(source_val - source_min) * > > + (target_max - target_min), source_max - source_min); > > target_val += target_min; > > > > return target_val; > > -- > > 1.9.3 > > > > _______________________________________________ > > Intel-gfx mailing list > > Intel-gfx@lists.freedesktop.org > > http://lists.freedesktop.org/mailman/listinfo/intel-gfx > _______________________________________________ Intel-gfx mailing list Intel-gfx@lists.freedesktop.org http://lists.freedesktop.org/mailman/listinfo/intel-gfx