[PATCH v2] drm/amdgpu/OLAND: clip the ref divider max value
Christian König
christian.koenig at amd.com
Fri Aug 20 06:38:13 UTC 2021
Sounds like a good idea to me, but I would limit this generally or at
least for the whole generation and not just one particular chipset.
Regards,
Christian.
Am 20.08.21 um 08:05 schrieb Sharma, Shashank:
> From 4841e5ba60e33ff798bde6cb69fbd7e137b6db9c Mon Sep 17 00:00:00 2001
> From: Shashank Sharma <shashank.sharma at amd.com>
> Date: Fri, 20 Aug 2021 10:20:02 +0530
> Subject: [PATCH v2] 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 at 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 at 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 at amd.com>
> Acked-by: Christian König <christian.koenig at amd.com>
>
> V2:
> - Restricting the changes only for OLAND, just to avoid any regression
> for other cards.
> - Changed unsigned -> unsigned int to make checkpatch quiet.
>
> Cc: Alex Deucher <Alexander.Deucher at amd.com>
> Cc: Christian König <christian.koenig at amd.com>
> Cc: Eddy Qin <Eddy.Qin at amd.com>
> Signed-off-by: Shashank Sharma <shashank.sharma at amd.com>
> ---
> 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..6d04c1d25bfb 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->asic_type == CHIP_OLAND)
> + 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,
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