From 673e7bbdb3920b62cfc6c710bea626b0a9b0f43a Mon Sep 17 00:00:00 2001 From: "U. Artie Eoff" Date: Mon, 29 Sep 2014 15:49:32 -0700 Subject: drm/i915: intel_backlight scale() math WA 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 Note that for easier backporting this commit adds a duplicated macro. A follow-up cleanup patch rectifies this for 3.18+ 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 Cc: stable@vger.kernel.org Reviewed-By: Joe Konno [danvet: Add backporting note.] Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_panel.c | 8 +++++--- 1 file changed, 5 insertions(+), 3 deletions(-) (limited to 'drivers/gpu/drm/i915/intel_panel.c') diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index 18784470a760..97ff71f40dd3 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; -- cgit v1.2.3 From 2e5416252af5239ddcd92bc858a494c1ca842778 Mon Sep 17 00:00:00 2001 From: "U. Artie Eoff" Date: Mon, 29 Sep 2014 15:49:33 -0700 Subject: drm/i915: Move DIV_ROUND_CLOSEST_ULL macro to header Move the duplicated DIV_ROUND_CLOSEST_ULL macro into the intel_drv.h header file so that it can be shared between intel_display.c and intel_panel.c. Signed-off-by: U. Artie Eoff Reviewed-By: Joe Konno Signed-off-by: Daniel Vetter --- drivers/gpu/drm/i915/intel_display.c | 3 --- drivers/gpu/drm/i915/intel_drv.h | 3 +++ drivers/gpu/drm/i915/intel_panel.c | 3 --- 3 files changed, 3 insertions(+), 6 deletions(-) (limited to 'drivers/gpu/drm/i915/intel_panel.c') diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c index 507370513f3d..6a0cc367934d 100644 --- a/drivers/gpu/drm/i915/intel_display.c +++ b/drivers/gpu/drm/i915/intel_display.c @@ -73,9 +73,6 @@ static const uint32_t intel_cursor_formats[] = { DRM_FORMAT_ARGB8888, }; -#define DIV_ROUND_CLOSEST_ULL(ll, d) \ -({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; }) - static void intel_increase_pllclock(struct drm_device *dev, enum pipe pipe); static void intel_crtc_update_cursor(struct drm_crtc *crtc, bool on); diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h index 07ce04683c30..ba715229a540 100644 --- a/drivers/gpu/drm/i915/intel_drv.h +++ b/drivers/gpu/drm/i915/intel_drv.h @@ -35,6 +35,9 @@ #include #include +#define DIV_ROUND_CLOSEST_ULL(ll, d) \ +({ unsigned long long _tmp = (ll)+(d)/2; do_div(_tmp, d); _tmp; }) + /** * _wait_for - magic (register) wait macro * diff --git a/drivers/gpu/drm/i915/intel_panel.c b/drivers/gpu/drm/i915/intel_panel.c index 97ff71f40dd3..0e018cb49147 100644 --- a/drivers/gpu/drm/i915/intel_panel.c +++ b/drivers/gpu/drm/i915/intel_panel.c @@ -398,9 +398,6 @@ 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 * -- cgit v1.2.3