[PATCH] drm/amdgpu/display: restore AUX_DPHY_TX_CONTROL for DCN2.x

[Harry Wentland]

On 2021-02-16 12:28 p.m., Alex Deucher wrote:
> Commit 098214999c8f added fetching of the AUX_DPHY register
> values from the vbios, but it also changed the default values
> in the case when there are no values in the vbios.  This causes
> problems with displays with high refresh rates.  To fix this,
> switch back to the original default value for AUX_DPHY_TX_CONTROL.

I don't see how this impacts displays with high refresh rates 
specifically. This is a change that only affects our AUX pre-charge time 
and was provided to us by the HW team. It does depend on another 
register being programmed by the VBIOS/DMCUBFW at boot.

Before we revert this I would like confirmation that this is the root of 
the problem.

Harry

> 
> Fixes: 098214999c8f ("drm/amd/display: Read VBIOS Golden Settings Tbl")
> Bug: https://gitlab.freedesktop.org/drm/amd/-/issues/1426
> Signed-off-by: Alex Deucher <alexander.deucher at amd.com>
> Cc: Igor Kravchenko <Igor.Kravchenko at amd.com>
> Cc: Aric Cyr <Aric.Cyr at amd.com>
> Cc: Aurabindo Pillai <aurabindo.pillai at amd.com>
> ---
>   drivers/gpu/drm/amd/display/dc/dcn20/dcn20_link_encoder.c | 3 +--
>   1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_link_encoder.c b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_link_encoder.c
> index fa013496e26b..2f9bfaeaba8d 100644
> --- a/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_link_encoder.c
> +++ b/drivers/gpu/drm/amd/display/dc/dcn20/dcn20_link_encoder.c
> @@ -341,8 +341,7 @@ void enc2_hw_init(struct link_encoder *enc)
>   	} else {
>   		AUX_REG_WRITE(AUX_DPHY_RX_CONTROL0, 0x103d1110);
>   
> -		AUX_REG_WRITE(AUX_DPHY_TX_CONTROL, 0x21c4d);
> -
> +		AUX_REG_WRITE(AUX_DPHY_TX_CONTROL, 0x21c7a);
>   	}
>   
>   	//AUX_DPHY_TX_REF_CONTROL'AUX_TX_REF_DIV HW default is 0x32;
>