Hi, On 09/24/2014 05:54 PM, Joe Konno wrote: > From: Joe Konno <joe.konno@xxxxxxxxx> > > 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 I wonder why do scaling at all, why not simply shift hw_min - hw_max range to 0 - (hw_max - hw_min) range and set max_brightness as seen by userspace to (hw_max - hw_min) ? Regards, Hans > > Signed-off-by: Joe Konno <joe.konno@xxxxxxxxx> > --- > drivers/gpu/drm/i915/intel_panel.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c > index f17ada3..dcdfbb3 100644 > --- a/drivers/gpu/drm/i915/intel_panel.c > +++ b/drivers/gpu/drm/i915/intel_panel.c > @@ -421,7 +421,7 @@ static uint32_t scale(uint32_t source_val, > /* 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(target_val, source_max - source_min); > target_val += target_min; > > return target_val; > _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
