[PATCH] drm/amd/display: disable FPO and SubVP for older DMUB versions on DCN32x

[Mario Limonciello]

On 12/15/2023 10:01, Hamza Mahfooz wrote:
> There have recently been changes that break backwards compatibility,
> that were introduced into DMUB firmware (for DCN32x) concerning FPO and
> SubVP. So, since those are just power optimization features, we can just
> disable them unless the user is using a new enough version of DMUB
> firmware.
> 
> Cc: stable at vger.kernel.org
> Link: https://gitlab.freedesktop.org/drm/amd/-/issues/2870
> Fixes: ed6e2782e974 ("drm/amd/display: For cursor P-State allow for SubVP")
> Reported-by: Mikhail Gavrilov <mikhail.v.gavrilov at gmail.com>
> Closes: https://lore.kernel.org/r/CABXGCsNRb0QbF2pKLJMDhVOKxyGD6-E+8p-4QO6FOWa6zp22_A@mail.gmail.com/
> Signed-off-by: Hamza Mahfooz <hamza.mahfooz at amd.com>

Reviewed-by: Mario Limonciello <mario.limonciello at amd.com>

> ---
>   drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c | 6 ++++++
>   1 file changed, 6 insertions(+)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c b/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
> index 5c323718ec90..0f0972ad441a 100644
> --- a/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
> +++ b/drivers/gpu/drm/amd/display/dc/hwss/dcn32/dcn32_hwseq.c
> @@ -960,6 +960,12 @@ void dcn32_init_hw(struct dc *dc)
>   		dc->caps.dmub_caps.subvp_psr = dc->ctx->dmub_srv->dmub->feature_caps.subvp_psr_support;
>   		dc->caps.dmub_caps.gecc_enable = dc->ctx->dmub_srv->dmub->feature_caps.gecc_enable;
>   		dc->caps.dmub_caps.mclk_sw = dc->ctx->dmub_srv->dmub->feature_caps.fw_assisted_mclk_switch;
> +
> +		if (dc->ctx->dmub_srv->dmub->fw_version <
> +		    DMUB_FW_VERSION(7, 0, 35)) {
> +			dc->debug.force_disable_subvp = true;
> +			dc->debug.disable_fpo_optimizations = true;
> +		}

One potential improvement would be to emit a message in this case to let 
the user know that this has happened and if they upgrade their firmware 
they can get additional power optimizations.

>   	}
>   }
>