drm/msm/dsi Lane-swapping for 2-lane panels non-functional for msm8x74?

[Johansson, Werner]

Hi,

I'm having issues with non-functional DSI output driving a 2-lane panel connected to DSI0 on MSM8x74 MDP5 v1.2 hardware. The code in drivers/gpu/drm/msm/dsi/dsi_host.c around line 703 enables lane 1 and 2 instead of lane 0 and 1 for performance reasons (and then enables lane swapping in the DSI PHY (LANE_SWAP_1230)). I cannot get this to work on the MSM8x74, no data observed on physical lane 0 (can't access lane1 easily unfortunately). Disabling this swap and enabling lane0 and 1 instead results in a fully functional panel.

Would it make sense to make this performance optimization a compile-time option that defaults to off (for certain problematic hardware or in general)?

/wj