From 7301757ea1fbead24f7c5687f828940a698a95db Mon Sep 17 00:00:00 2001 From: Shashank Sharma Date: Fri, 20 Aug 2021 10:20:02 +0530 Subject: drm/amdgpu/OLAND: clip the ref divider max value MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 V1: Got acks from: Acked-by: Alex Deucher Acked-by: Christian König V2: - Restricting the changes only for OLAND, just to avoid any regression for other cards. - Changed unsigned -> unsigned int to make checkpatch quiet. V3: Apply the change on SI family (not only oland) (Christian) Cc: Alex Deucher Cc: Christian König Cc: Eddy Qin Reviewed-by: Christian König Signed-off-by: Shashank Sharma Signed-off-by: Alex Deucher --- drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) (limited to 'drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h') diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h index db6136f68b82..44a583d6c9b4 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h @@ -24,7 +24,8 @@ #ifndef __AMDGPU_PLL_H__ #define __AMDGPU_PLL_H__ -void amdgpu_pll_compute(struct amdgpu_pll *pll, +void amdgpu_pll_compute(struct amdgpu_device *adev, + struct amdgpu_pll *pll, u32 freq, u32 *dot_clock_p, u32 *fb_div_p, -- cgit v1.2.3-70-g09d2