Re: [PATCH 6.12.y/6.18.y/7.1.y] drm/amd/display: Fix DTB DTO updates breaking live pixel rate sources

[Mario Limonciello <superm1@kernel.org>]

On 7/29/26 01:33, Matthew Schwartz wrote:
> From: Harry Wentland <harry.wentland@amd.com>
> 
> commit 76a2db58e95e328007043f54ac3c7336ccbee440 upstream.
> 
> dcn32_update_clocks_update_dtb_dto() and its dcn35 counterpart reprogram
> the DTB DTO of every timing generator in the context whenever the DTBCLK
> reference changes, passing a zeroed pixel rate and never setting
> is_hdmi. Both dccg set_dtbclk_dto() implementations treat a zero pixel
> rate as a disable request. On dcn32 that branch drives PIPE_DTO_SRC_SEL
> to the DP DTO source, so a timing generator actively scanning out an
> HDMI stream has its pixel rate source re-muxed out from under the live
> raster and the OTG stops on the spot. On dcn35 it clears
> DTBCLK_DTO_ENABLE and restores DTBCLK_Pn clock gating, which does the
> same to a live 128b/132b stream.
> 
> Two displays where only one runs a 128b/132b link hit this reliably.
> is_dtbclk_required() holds the DTBCLK reference high while both are
> active, and the moment the 128b/132b stream is torn down (compositor
> switch, display disable, hot-unplug) the next safe_to_lower pass drops
> the reference to the lowest DPM level and the DTO walk freezes the
> surviving screen. On Navi31 the DAL mailbox then goes deaf on the
> DISPCLK hard-min that follows the walk in dcn32_update_clocks(),
> stranding both SMU mailboxes until reboot.
> 
> Set is_hdmi for HDMI and DVI signals so the disable path leaves the
> pixel rate source selection on the HDMI path, and pass the real pixel
> rate for 128b/132b streams so a reference change rescales their DTO
> instead of disabling it.
> 
> Fixes: 128c1ca0303f ("drm/amd/display: Update DTBCLK for DCN32")
> Fixes: 8774029f76b9 ("drm/amd/display: Add DCN35 CLK_MGR")
> Signed-off-by: Harry Wentland <harry.wentland@amd.com>
> Reviewed-by: Fangzhi Zuo <Jerry.Zuo@amd.com>
> Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
> Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
> [ mschwartz: dcn32 and dcn35 clk_mgr hunks only. The rest is HDMI FRL
>    enablement, absent before 7.2, so the FRL conditions and the
>    req_audio_dtbclk_khz assignment they guard are dropped and the
>    FRL-centric changelog is rewritten. Added the pipe_ctx->stream check
>    the new dereferences need. ]
> Signed-off-by: Matthew Schwartz <matthew.schwartz@linux.dev>
> ---
> 6.6.y needs the dcn32 hunk alone and is sent alongside this one. Tested
> on Navi31 with a DisplayPort UHBR monitor and an HDMI TV.
Backport makes sense to me, thanks.

Reviewed-by: Mario Limonciello (AMD) <superm1@kernel.org>
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn32/dcn32_clk_mgr.c b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn32/dcn32_clk_mgr.c
> index 084994c650c4..285689d7ecc4 100644
> --- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn32/dcn32_clk_mgr.c
> +++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn32/dcn32_clk_mgr.c
> @@ -276,13 +276,20 @@ static void dcn32_update_clocks_update_dtb_dto(struct clk_mgr_internal *clk_mgr,
>   		struct dtbclk_dto_params dto_params = {0};
>   
>   		/* use mask to program DTO once per tg */
> -		if (pipe_ctx->stream_res.tg &&
> +		if (pipe_ctx->stream && pipe_ctx->stream_res.tg &&
>   				!(tg_mask & (1 << pipe_ctx->stream_res.tg->inst))) {
>   			tg_mask |= (1 << pipe_ctx->stream_res.tg->inst);
>   
>   			dto_params.otg_inst = pipe_ctx->stream_res.tg->inst;
>   			dto_params.ref_dtbclk_khz = ref_dtbclk_khz;
>   
> +			if (dccg->ctx->dc->link_srv->dp_is_128b_132b_signal(pipe_ctx))
> +				dto_params.pixclk_khz = pipe_ctx->stream->timing.pix_clk_100hz / 10;
> +
> +			if (dc_is_hdmi_signal(pipe_ctx->stream->signal) ||
> +					dc_is_dvi_signal(pipe_ctx->stream->signal))
> +				dto_params.is_hdmi = true;
> +
>   			dccg->funcs->set_dtbclk_dto(clk_mgr->dccg, &dto_params);
>   			//dccg->funcs->set_audio_dtbclk_dto(clk_mgr->dccg, &dto_params);
>   		}
> diff --git a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c
> index bb1ac12a2b09..d154383a3961 100644
> --- a/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c
> +++ b/drivers/gpu/drm/amd/display/dc/clk_mgr/dcn35/dcn35_clk_mgr.c
> @@ -264,13 +264,20 @@ static void dcn35_update_clocks_update_dtb_dto(struct clk_mgr_internal *clk_mgr,
>   		struct dtbclk_dto_params dto_params = {0};
>   
>   		/* use mask to program DTO once per tg */
> -		if (pipe_ctx->stream_res.tg &&
> +		if (pipe_ctx->stream && pipe_ctx->stream_res.tg &&
>   				!(tg_mask & (1 << pipe_ctx->stream_res.tg->inst))) {
>   			tg_mask |= (1 << pipe_ctx->stream_res.tg->inst);
>   
>   			dto_params.otg_inst = pipe_ctx->stream_res.tg->inst;
>   			dto_params.ref_dtbclk_khz = ref_dtbclk_khz;
>   
> +			if (dccg->ctx->dc->link_srv->dp_is_128b_132b_signal(pipe_ctx))
> +				dto_params.pixclk_khz = pipe_ctx->stream->timing.pix_clk_100hz / 10;
> +
> +			if (dc_is_hdmi_signal(pipe_ctx->stream->signal) ||
> +					dc_is_dvi_signal(pipe_ctx->stream->signal))
> +				dto_params.is_hdmi = true;
> +
>   			dccg->funcs->set_dtbclk_dto(clk_mgr->dccg, &dto_params);
>   			//dccg->funcs->set_audio_dtbclk_dto(clk_mgr->dccg, &dto_params);
>   		}