[PATCH 0/5] drm/bridge: samsung-dsim: fix various modes with ADV7535 bridge

[Michael Tretter]

I tested the i.MX8M Nano EVK with the NXP supplied MIPI-DSI adapter,
which uses an ADV7535 MIPI-DSI to HDMI converter. I found that a few
modes were working, but in many modes my monitor stayed dark.

This series fixes the Samsung DSIM bridge driver to bring up a few more
modes:

The driver read the rate of the PLL ref clock only during probe.
However, if the clock is re-parented to the VIDEO_PLL, changes to the
pixel clock have an effect on the PLL ref clock. Therefore, the driver
must read and potentially update the PLL ref clock on every modeset.

I also found that the rounding mode of the porches and active area has
an effect on the working modes. If the driver rounds up instead of
rounding down and be calculates them in Hz instead of kHz, more modes
start to work.

The following table shows the modes that were working in my test without
this patch set and the modes that are working now:

|            Mode | Before | Now |
| 1920x1080-60.00 | X      | X   |
| 1920x1080-59.94 |        | X   |
| 1920x1080-50.00 |        | X   |
| 1920x1080-30.00 |        | X   |
| 1920x1080-29.97 |        | X   |
| 1920x1080-25.00 |        | X   |
| 1920x1080-24.00 |        |     |
| 1920x1080-23.98 |        |     |
| 1680x1050-59.88 |        | X   |
| 1280x1024-75.03 | X      | X   |
| 1280x1024-60.02 | X      | X   |
|  1200x960-59.99 |        | X   |
|  1152x864-75.00 | X      | X   |
|  1280x720-60.00 |        |     |
|  1280x720-59.94 |        |     |
|  1280x720-50.00 |        | X   |
|  1024x768-75.03 |        | X   |
|  1024x768-60.00 |        | X   |
|   800x600-75.00 | X      | X   |
|   800x600-60.32 | X      | X   |
|   720x576-50.00 | X      | X   |
|   720x480-60.00 |        |     |
|   720x480-59.94 | X      |     |
|   640x480-75.00 | X      | X   |
|   640x480-60.00 |        | X   |
|   640x480-59.94 |        | X   |
|   720x400-70.08 |        |     |

Interestingly, the 720x480-59.94 mode stopped working. However, I am
able to bring up the 720x480 modes by manually hacking the active area
(hsa) to 40 and carefully adjusting the clocks, but something still
seems to be off.

Unfortunately, a few more modes are still not working at all. The NXP
downstream kernel has some quirks to handle some of the modes especially
wrt. to the porches, but I cannot figure out, what the driver should
actually do in these cases. Maybe there is still an error in the
calculation of the porches and someone at NXP can chime in.

Michael

Signed-off-by: Michael Tretter <m.tretter@xxxxxxxxxxxxxx>
---
Marco Felsch (1):
      drm/bridge: samsung-dsim: add more mipi-dsi device debug information

Michael Tretter (4):
      drm/bridge: samsung-dsim: reread ref clock before configuring PLL
      drm/bridge: samsung-dsim: update PLL reference clock
      drm/bridge: samsung-dsim: adjust porches by rounding up
      drm/bridge: samsung-dsim: calculate porches in Hz

 drivers/gpu/drm/bridge/samsung-dsim.c | 42 +++++++++++++++++++++++++----------
 include/drm/bridge/samsung-dsim.h     |  1 +
 2 files changed, 31 insertions(+), 12 deletions(-)
---
base-commit: 2dde18cd1d8fac735875f2e4987f11817cc0bc2c
change-id: 20230818-samsung-dsim-42346444bce5

Best regards,
-- 
Michael Tretter <m.tretter@xxxxxxxxxxxxxx>