On Wed, 24 Sep 2014, Hans de Goede <hdegoede@xxxxxxxxxx> wrote: > 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) ? Mostly in preparation for a future where we expose an arbitrary range, say 0..100 or 0..255 to the userspace. BR, Jani. > > 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 -- Jani Nikula, Intel Open Source Technology Center _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx http://lists.freedesktop.org/mailman/listinfo/intel-gfx
