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 <alexander.deucher@xxxxxxx> Acked-by: Christian König <christian.koenig@xxxxxxx> 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 <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 | 20 +++++++++++++------- drivers/gpu/drm/amd/amdgpu/amdgpu_pll.h | 3 ++- drivers/gpu/drm/amd/amdgpu/atombios_crtc.c | 2 +- 3 files changed, 16 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c index f2e20666c9c1..4eaec446b49d 100644 --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c @@ -80,12 +80,17 @@ static void amdgpu_pll_reduce_ratio(unsigned *nom, unsigned *den, * Calculate feedback and reference divider for a given post divider. Makes * sure we stay within the limits. */ -static void amdgpu_pll_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_div, - unsigned fb_div_max, unsigned ref_div_max, - unsigned *fb_div, unsigned *ref_div) +static void amdgpu_pll_get_fb_ref_div(struct amdgpu_device *adev, unsigned int nom, + unsigned int den, unsigned int post_div, + unsigned int fb_div_max, unsigned int ref_div_max, + unsigned int *fb_div, unsigned int *ref_div) { + /* limit reference * post divider to a maximum */ - ref_div_max = min(128 / post_div, ref_div_max); + if (adev->family == AMDGPU_FAMILY_SI) + ref_div_max = min(100 / post_div, ref_div_max); + else + ref_div_max = min(128 / 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); @@ -112,7 +117,8 @@ static void amdgpu_pll_get_fb_ref_div(unsigned nom, unsigned den, unsigned post_ * Try to calculate the PLL parameters to generate the given frequency: * dot_clock = (ref_freq * feedback_div) / (ref_div * post_div) */ -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, @@ -199,7 +205,7 @@ void amdgpu_pll_compute(struct amdgpu_pll *pll, for (post_div = post_div_min; post_div <= post_div_max; ++post_div) { unsigned diff; - amdgpu_pll_get_fb_ref_div(nom, den, post_div, fb_div_max, + amdgpu_pll_get_fb_ref_div(adev, nom, den, post_div, fb_div_max, ref_div_max, &fb_div, &ref_div); diff = abs(target_clock - (pll->reference_freq * fb_div) / (ref_div * post_div)); @@ -214,7 +220,7 @@ void amdgpu_pll_compute(struct amdgpu_pll *pll, post_div = post_div_best; /* get the feedback and reference divider for the optimal value */ - amdgpu_pll_get_fb_ref_div(nom, den, post_div, fb_div_max, ref_div_max, + amdgpu_pll_get_fb_ref_div(adev, nom, den, post_div, fb_div_max, ref_div_max, &fb_div, &ref_div); /* reduce the numbers to a simpler ratio once more */ 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, diff --git a/drivers/gpu/drm/amd/amdgpu/atombios_crtc.c b/drivers/gpu/drm/amd/amdgpu/atombios_crtc.c index 159a2a4385a1..afad094f84c2 100644 --- a/drivers/gpu/drm/amd/amdgpu/atombios_crtc.c +++ b/drivers/gpu/drm/amd/amdgpu/atombios_crtc.c @@ -851,7 +851,7 @@ void amdgpu_atombios_crtc_set_pll(struct drm_crtc *crtc, struct drm_display_mode pll->reference_div = amdgpu_crtc->pll_reference_div; pll->post_div = amdgpu_crtc->pll_post_div; - amdgpu_pll_compute(pll, amdgpu_crtc->adjusted_clock, &pll_clock, + amdgpu_pll_compute(adev, pll, amdgpu_crtc->adjusted_clock, &pll_clock, &fb_div, &frac_fb_div, &ref_div, &post_div); amdgpu_atombios_crtc_program_ss(adev, ATOM_DISABLE, amdgpu_crtc->pll_id, -- 2.25.1