[PATCH v2 0/6] Pinephone video out fixes (flipping between two frames)

[Frank Oltmanns <frank@oltmanns.dev>]

On some pinephones the video output sometimes freezes (flips between two
frames) [1]. It seems to be that the reason for this behaviour is that
PLL-MIPI, PLL-GPU and GPU are operating outside their limits.

In this patch series I propose the followin changes:
  1. sunxi-ng: Adhere to the following constraints given in the
     Allwinner A64 Manual regarding PLL-MIPI:
      * M/N <= 3
      * (PLL_VIDEO0)/M >= 24MHz
      * 500MHz <= clockrate <= 1400MHz

  2. Choose a higher clock rate for the ST7703 based XDB599 panel, so
     that the panel function well with the Allwinner A64 SOC. PLL-MIPI
     must run between 500 MHz and 1.4 GHz. As PLL-MIPI runs at 6 times
     the panel's clock rate, we need the panel's clock to be at least
     83.333 MHz.

  3. Increase the minimum frequency in the A64 DTS OPPs from 120 MHz to
     192 MHz. This further reduces the issue.

Unfortunately, with these patches the issue [1] is not completely gone,
but becomes less likely.

Note, that when pinning the GPU to 432 MHz the issue completely
disappears for me. I've searched the BSP and could not find any
indication that supports the idea of having the three OPPs. The only
frequency I found in the BPSs for A64 is 432 MHz, that has also proven
stable for me. So, while increasing the minimum frequency to 192 MHz
reduces the issue, should we maybe instead set the GPU to a fixed 432
MHz instead?

I very much appreciate your feedback!

[1] https://gitlab.com/postmarketOS/pmaports/-/issues/805

Signed-off-by: Frank Oltmanns <frank@oltmanns.dev>
---
Changes in v2:
- dts: Increase minimum GPU frequency to 192 MHz.
- nkm and a64: Add minimum and maximum rate for PLL-MIPI.
- nkm: Use the same approach for skipping invalid rates in
  ccu_nkm_find_best() as in ccu_nkm_find_best_with_parent_adj().
- nkm: Improve names for ratio struct members and hence get rid of
  describing comments.
- nkm and a64: Correct description in the commit messages: M/N <= 3
- Remove patches for nm as they were not needed.
- st7703: Rework the commit message to cover more background for the
  change.
- Link to v1: https://lore.kernel.org/r/20231218-pinephone-pll-fixes-v1-0-e238b6ed6dc1@oltmanns.dev

---
Frank Oltmanns (6):
      clk: sunxi-ng: nkm: Support constraints on m/n ratio and parent rate
      clk: sunxi-ng: a64: Add constraints on PLL-MIPI's n/m ratio and parent rate
      clk: sunxi-ng: nkm: Support minimum and maximum rate
      clk: sunxi-ng: a64: Set minimum and maximum rate for PLL-MIPI
      drm/panel: st7703: Drive XBD599 panel at higher clock rate
      arm64: dts: allwinner: a64: Fix minimum GPU OPP rate

 arch/arm64/boot/dts/allwinner/sun50i-a64.dtsi |  4 ++--
 drivers/clk/sunxi-ng/ccu-sun50i-a64.c         | 14 +++++++----
 drivers/clk/sunxi-ng/ccu_nkm.c                | 34 +++++++++++++++++++++++++++
 drivers/clk/sunxi-ng/ccu_nkm.h                |  4 ++++
 drivers/gpu/drm/panel/panel-sitronix-st7703.c | 14 +++++------
 5 files changed, 56 insertions(+), 14 deletions(-)
---
base-commit: 059c53e877ca6e723e10490c27c1487a63e66efe
change-id: 20231218-pinephone-pll-fixes-0ccdfde273e4

Best regards,
-- 
Frank Oltmanns <frank@oltmanns.dev>