On Tue, 2017-06-06 at 19:46 +0200, Mario Kleiner wrote: > On Thu, Jun 1, 2017 at 1:13 PM, Ben Hutchings > <ben.hutchi...@codethink.co.uk> wrote: > > On Tue, 2017-05-23 at 22:08 +0200, Greg Kroah-Hartman wrote: > >> 4.4-stable review patch. If anyone has any objections, please let me know. > >> > >> ------------------ > >> > >> From: Mario Kleiner <mario.kleiner...@gmail.com> > >> > >> commit d63c277dc672e0c568481af043359420fa9d4736 upstream. > >> > >> Avoid big roundoff errors in scanline/hactive durations for > >> high pixel clocks, especially for >= 500 Mhz, and thereby > >> program more accurate display fifo watermarks. > > [...] > >> --- a/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c > >> +++ b/drivers/gpu/drm/amd/amdgpu/dce_v10_0.c > >> @@ -1237,14 +1237,14 @@ static void dce_v10_0_program_watermarks > >> { > >> struct drm_display_mode *mode = &amdgpu_crtc->base.mode; > >> struct dce10_wm_params wm_low, wm_high; > >> - u32 pixel_period; > >> + u32 active_time; > >> u32 line_time = 0; > >> u32 latency_watermark_a = 0, latency_watermark_b = 0; > >> u32 tmp, wm_mask, lb_vblank_lead_lines = 0; > >> > >> if (amdgpu_crtc->base.enabled && num_heads && mode) { > >> - pixel_period = 1000000 / (u32)mode->clock; > >> - line_time = min((u32)mode->crtc_htotal * pixel_period, > >> (u32)65535); > >> + active_time = 1000000UL * (u32)mode->crtc_hdisplay / > >> (u32)mode->clock; > >> + line_time = min((u32) (1000000UL * (u32)mode->crtc_htotal / > >> (u32)mode->clock), (u32)65535); > > [...] > > > > Won't these multiplications overflow if a >4K display is attached to a > > 32-bit machine? > > > > Ben. > > > > Yes, indeed > 4k causes a new overflow problem! Thanks for catching this. > I will prepare a follow-up patch on top of this one, to use ... > > active_time = (u32) div_u64((u64) mode->crtc_hdisplay * 1000000, > (u32)mode->clock); > line_time = (u32) div_u64((u64) mode->crtc_htotal * 1000000, > (u32)mode->clock); > line_time = min(line_time, (u32) 65535); > > ...instead. > > Ok?
I think that would work. Ben. -- Ben Hutchings Software Developer, Codethink Ltd.