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7301757ea1
mirror_ubuntu-kernels/drivers/gpu
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Shashank Sharma 7301757ea1 drm/amdgpu/OLAND: clip the ref divider max value 
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:
4b21ce1b4b

V1:
Got acks from:
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Acked-by: Christian König <christian.koenig@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@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Eddy Qin <Eddy.Qin@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Shashank Sharma <shashank.sharma@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
2021-08-24 15:35:25 -04:00
..
drm drm/amdgpu/OLAND: clip the ref divider max value 2021-08-24 15:35:25 -04:00
host1x gpu: host1x: Split up client initalization and registration 2021-05-17 12:31:05 +02:00
ipu-v3 gpu: ipu-v3: Add Rec.709 limited range support to DP 2021-05-10 17:20:29 +02:00
trace
vga vgaarb: don't pass a cookie to vga_client_register 2021-07-21 10:29:10 +02:00
Makefile