[H/OEM-5.10][PATCH 0/1] i915 doesn't support some high pixel clock 4k * 60Hz monitors

[Jeremy Szu]

BugLink: https://bugs.launchpad.net/bugs/1922372

[Impact]

 * Some 4K monitors can not display as maximum resolution from i915 graphic.

 * In some 4k monitors, it's support higher pixel clock

The following is the case I have:

Modeline "Mode 0" 533.25 3840 3888 3920 4000 2160 2163 2168 2222 +hsync -vsync

Which will be dropped because the mode rate is greater than i915 maximum data rate.
kernel: [drm:drm_mode_debug_printmodeline [drm]] Modeline "3840x2160": 60 533250 3840 3888 3920 4000 2160 2163 2168 2222 0x48 0x9
kernel: [drm:drm_mode_prune_invalid [drm]] Not using 3840x2160 mode: CLOCK_HIGH

The BDB version of Intel vBIOS is 237
kernel: i915 0000:00:02.0: [drm:intel_bios_init [i915]] VBT signature "$VBT TIGERLAKE ", BDB version 237

In old i915 parsing rule (for greater than v216), the common rate is decoded as 16200
kernel: i915 0000:00:02.0: [drm:intel_dp_print_rates [i915]] common rates: 162000

Since the Intel updated the parsing rule (for greater then 230). the common rate is up to 540000
kernel: i915 0000:00:02.0: [drm:intel_dp_print_rates [i915]] common rates: 162000, 270000,
 540000

There are 4 lanes support.
i915 0000:00:02.0: [drm:intel_dp_link_train_phy [i915]] [CONNECTOR:184:DP-2] Link
Training passed at link rate = 162000, lane count = 4, at DPRX

In this monitor, the max rate (max_link_clock * max_lanes) is:
162000 * 4 = 648000 # if using old parsing rule (> 210)
540000 * 4 = 2160000 # if using updated parsing rule (> 230)

the maximum mode rate is
DIV_ROUND_UP(pixel_clock * bpp, 8);

the bpp here is minimum bpp, which is 6 * 3 = 18
...
 max bpc: 12
  range: (6, 12)
...
thus:
533250 * 18 + 8 - 1 / 8 = 1199813 # this is maximum mode rate of this monitor.

[Fix]

 * It needs to use the updated parsing table (intel BDB table version > 230) for supporting high pixel clock monitors.

[Test Plan]

 * Steps to reproduce
  1. Connect a high pixel clock monitor (533KHz in my case) to i915 graphic which vbios version is v237 (In my case:
 ModelName "U2879G6"
 VendorName "AOC"

  2. Check the display setting, expect a 3840*2160*60Hz option but there is not 3840*2160*60Hz option.

 * if upgrade drm debugging level then you will see the modeline be dropped because of high clock.
kernel: [drm:drm_mode_prune_invalid [drm]] Not using 3840x2160 mode: CLOCK_HIGH

 * after applying the change, the resolution work good.

[Where problems could occur]

 * This change considered the backward compatibility, which will check the BDB version before applying different parsing rule.

 * From software perspective, the monitor will show nothing if Intel vBIOS using BDB > 230 with undefined dp_max_link_rate field.

 * Otherwise, it looks quite ok.

Lee Shawn C (1):
  drm/i915/vbt: update DP max link rate table

 drivers/gpu/drm/i915/display/intel_bios.c     | 58 ++++++++++++++-----
 drivers/gpu/drm/i915/display/intel_vbt_defs.h | 23 ++++++--
 2 files changed, 60 insertions(+), 21 deletions(-)

-- 
2.30.1