Re: [PATCH] drm/msm/dpu: round up the compressed INTF width

[Dmitry Baryshkov]

On Sun, Oct 04, 2026 at 07:27:58PM +0900, Joonhoe Kim wrote:
> For DSI with DSC, drm_mode_to_intf_timing_params() scales the INTF
> active width by bpp / (3 * bits_per_component) and rounds down. The DSI
> host computes the same width with DIV_ROUND_UP, both for the pixel clock
> (dsi_adjust_pclk_for_compression()) and for the active width it programs
> (dsi_timing_setup(), from bytes per line). When the division is not
> exact the INTF line is one pclk shorter than the DSI line, and the DSI
> FIFO overflows.
> 
> Example: a bonded DSI video-mode panel, 952 pixels per link, DSC 8 bpp at
> 10 bpc: 952 * 8 / 30 = 253.87, so the INTF uses 253 and the DSI 254.
> 
> Round up, as the DSI host does. Qualcomm's downstream SDE driver also
> rounds this width up, and Pengyu Luo needed the same rounding on the
> Legion Y700 gen 4 [1].
> 
> Tested on a Lenovo Legion Tab Y700 gen 5 (SM8850) with that panel, with a
> module parameter selecting the rounding: rounding down, DPMS off/on gives
> no vblank and 14000-17000 DSI FIFO error interrupts per second
> (dsi_err_worker: status=4); rounding up, the picture comes back and there
> are no errors. Only tested on this device.
> 
> Link: https://lore.kernel.org/all/CAH2e8h6oinKxN1ndcvHCSc+=bFLXVVDZVAVF0cQHoiaMvEwhPQ@xxxxxxxxxxxxxx/ [1]
> Fixes: f9ce482d7dc0 ("drm/msm/dpu: fix video mode DSC for DSI")
> Assisted-by: LLM
> Signed-off-by: Joonhoe Kim <26rote@xxxxxxxxx>
> ---

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@xxxxxxxxxxxxxxxx>

> 

-- 
With best wishes
Dmitry