This patch limits the ref_div_max value to 100, during the calculation of PLL feedback reference divider. With current value (128), the produced fb_ref_div value generates unstable output at particular frequencies. Radeon driver limits this value at 100. On Oland, when we try to setup mode 2048x1280@60 (a bit weird, I know), it demands a clock of 221270 Khz. It's been observed that the PLL calculations using values 128 and 100 are vastly different, and look like this: +------------------------------------------+ |Parameter |AMDGPU |Radeon | | | | | +-------------+----------------------------+ |Clock feedback | | |divider max | 128 | 100 | |cap value | | | | | | | | | | | +------------------------------------------+ |ref_div_max | | | | | 42 | 20 | | | | | | | | | +------------------------------------------+ |ref_div | 42 | 20 | | | | | +------------------------------------------+ |fb_div | 10326 | 8195 | +------------------------------------------+ |fb_div | 1024 | 163 | +------------------------------------------+ |fb_dev_p | 4 | 9 | |frac fb_de^_p| | | +----------------------------+-------------+ With ref_div_max value clipped at 100, AMDGPU driver can also drive videmode 2048x1280@60 (221Mhz) and produce proper output without any blanking and distortion on the screen. PS: This value was changed from 128 to 100 in Radeon driver also, here: https://github.com/freedesktop/drm-tip/commit/4b21ce1b4b5d262e7d4656b8ececc891fc3cb806 Cc: Alex Deucher <Alexander.Deucher@xxxxxxx> Cc: Christian König <christian.koenig@xxxxxxx> Cc: Eddy Qin <Eddy.Qin@xxxxxxx> Signed-off-by: Shashank Sharma <shashank.sharma@xxxxxxx> --- drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c index 1f2305b7bd13..23a2e1ebf78a 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c @@ -85,7 +85,7 @@ static void amdgpu_pll_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_ unsigned *fb_div, unsigned *ref_div) { /* limit reference * post divider to a maximum */ - ref_div_max = min(128 / post_div, ref_div_max); + ref_div_max = min(100 / post_div, ref_div_max); /* get matching reference and feedback divider */ *ref_div = min(max(DIV_ROUND_CLOSEST(den, post_div), 1u), ref_div_max); -- 2.25.1 _______________________________________________ amd-gfx mailing list amd-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/amd-gfx
