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Message-ID: <2f793737-17a1-7497-27c1-3feec713114b@amd.com>
Date: Mon, 5 Sep 2022 08:05:57 +0200
From: Christian König <christian.koenig@....com>
To: zhongpei <zhongpei@...inos.cn>, alexander.deucher@....com,
Xinhui.Pan@....com, airlied@...ux.ie, daniel@...ll.ch,
isabbasso@...eup.net
Cc: amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm:Fix the blank screen problem of some 1920x1080 75Hz
monitors using R520 graphics card
Am 05.09.22 um 05:23 schrieb zhongpei:
> We found that in the scenario of AMD R520 graphics card
> and some 1920x1080 monitors,when we switch the refresh rate
> of the monitor to 75Hz,the monitor will have a blank screen problem,
> and the restart cannot be restored.After testing, it is found that
> when we limit the maximum value of ref_div_max to 128,
> the problem can be solved.In order to keep the previous modification
> to be compatible with other monitors,we added a judgment
> when finding the minimum diff value in the loop of the
> amdgpu_pll_compute/radeon_compute_pll_avivo function.
> If no diff value of 0 is found when the maximum value of ref_div_max
> is limited to 100,continue to search when it is 128,
> and take the parameter with the smallest diff value.
Well that's at least better than what I've seen in previous tries to fix
this.
But as far as I can see this will certainly break some other monitors,
so that is pretty much a NAK.
Regards,
Christian.
>
> Signed-off-by: zhongpei <zhongpei@...inos.cn>
> ---
> drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c | 17 +++++++++++++----
> drivers/gpu/drm/radeon/radeon_display.c | 15 +++++++++++----
> 2 files changed, 24 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c
> index 0bb2466d539a..0c298faa0f94 100644
> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c
> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_pll.c
> @@ -84,12 +84,13 @@ static void amdgpu_pll_reduce_ratio(unsigned *nom, unsigned *den,
> 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)
> + unsigned int ref_div_limit, unsigned int *fb_div,
> + unsigned int *ref_div)
> {
>
> /* limit reference * post divider to a maximum */
> if (adev->family == AMDGPU_FAMILY_SI)
> - ref_div_max = min(100 / post_div, ref_div_max);
> + ref_div_max = min(ref_div_limit / post_div, ref_div_max);
> else
> ref_div_max = min(128 / post_div, ref_div_max);
>
> @@ -136,6 +137,7 @@ void amdgpu_pll_compute(struct amdgpu_device *adev,
> unsigned ref_div_min, ref_div_max, ref_div;
> unsigned post_div_best, diff_best;
> unsigned nom, den;
> + unsigned ref_div_limit, ref_limit_best;
>
> /* determine allowed feedback divider range */
> fb_div_min = pll->min_feedback_div;
> @@ -204,11 +206,12 @@ void amdgpu_pll_compute(struct amdgpu_device *adev,
> else
> post_div_best = post_div_max;
> diff_best = ~0;
> + ref_div_limit = ref_limit_best = 100;
>
> for (post_div = post_div_min; post_div <= post_div_max; ++post_div) {
> unsigned diff;
> amdgpu_pll_get_fb_ref_div(adev, nom, den, post_div, fb_div_max,
> - ref_div_max, &fb_div, &ref_div);
> + ref_div_max, ref_div_limit, &fb_div, &ref_div);
> diff = abs(target_clock - (pll->reference_freq * fb_div) /
> (ref_div * post_div));
>
> @@ -217,13 +220,19 @@ void amdgpu_pll_compute(struct amdgpu_device *adev,
>
> post_div_best = post_div;
> diff_best = diff;
> + ref_limit_best = ref_div_limit;
> }
> + if (post_div >= post_div_max && diff_best != 0 && ref_div_limit != 128) {
> + ref_div_limit = 128;
> + post_div = post_div_min - 1;
> + }
> +
> }
> post_div = post_div_best;
>
> /* get the feedback and reference divider for the optimal value */
> amdgpu_pll_get_fb_ref_div(adev, nom, den, post_div, fb_div_max, ref_div_max,
> - &fb_div, &ref_div);
> + ref_limit_best, &fb_div, &ref_div);
>
> /* reduce the numbers to a simpler ratio once more */
> /* this also makes sure that the reference divider is large enough */
> diff --git a/drivers/gpu/drm/radeon/radeon_display.c b/drivers/gpu/drm/radeon/radeon_display.c
> index f12675e3d261..0fcbf45a68db 100644
> --- a/drivers/gpu/drm/radeon/radeon_display.c
> +++ b/drivers/gpu/drm/radeon/radeon_display.c
> @@ -925,10 +925,10 @@ static void avivo_reduce_ratio(unsigned *nom, unsigned *den,
> */
> static void avivo_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)
> + unsigned ref_div_limit, unsigned *fb_div, unsigned *ref_div)
> {
> /* limit reference * post divider to a maximum */
> - ref_div_max = max(min(100 / post_div, ref_div_max), 1u);
> + ref_div_max = max(min(ref_div_limit / post_div, ref_div_max), 1u);
>
> /* get matching reference and feedback divider */
> *ref_div = min(max(den/post_div, 1u), ref_div_max);
> @@ -971,6 +971,7 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
> unsigned ref_div_min, ref_div_max, ref_div;
> unsigned post_div_best, diff_best;
> unsigned nom, den;
> + unsigned ref_div_limit, ref_limit_best;
>
> /* determine allowed feedback divider range */
> fb_div_min = pll->min_feedback_div;
> @@ -1042,11 +1043,12 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
> else
> post_div_best = post_div_max;
> diff_best = ~0;
> + ref_div_limit = ref_limit_best = 100;
>
> for (post_div = post_div_min; post_div <= post_div_max; ++post_div) {
> unsigned diff;
> avivo_get_fb_ref_div(nom, den, post_div, fb_div_max,
> - ref_div_max, &fb_div, &ref_div);
> + ref_div_max, ref_div_limit, &fb_div, &ref_div);
> diff = abs(target_clock - (pll->reference_freq * fb_div) /
> (ref_div * post_div));
>
> @@ -1055,13 +1057,18 @@ void radeon_compute_pll_avivo(struct radeon_pll *pll,
>
> post_div_best = post_div;
> diff_best = diff;
> + ref_limit_best = ref_div_limit;
> + }
> + if (post_div >= post_div_max && diff_best != 0 && ref_div_limit != 128) {
> + ref_div_limit = 128;
> + post_div = post_div_min - 1;
> }
> }
> post_div = post_div_best;
>
> /* get the feedback and reference divider for the optimal value */
> avivo_get_fb_ref_div(nom, den, post_div, fb_div_max, ref_div_max,
> - &fb_div, &ref_div);
> + ref_limit_best, &fb_div, &ref_div);
>
> /* reduce the numbers to a simpler ratio once more */
> /* this also makes sure that the reference divider is large enough */
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