[PATCH v3] drm/amdgpu/OLAND: clip the ref divider max value
Shashank Sharma
shashank.sharma at amd.com
Fri Aug 20 13:54:14 UTC 2021
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.
V3: Apply the change on SI family (not only oland) (Christian)
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..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
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