[PATCH v2] drm/dp: follow DP link CTS spec to read link status back

[Jani Nikula]

On Wed, 07 Jul 2021, Lee Shawn C <shawn.c.lee at intel.com> wrote:
> Refer to DP link CTS 1.2/1.4 spec, the following test case request
> source read DPCD 200h - 205h to get latest link status from sink.
>
> (4.3.2.4) Handling of IRQ HPD Pulse with No Error Status Bits Set
> (400.3.2.1) Successful Link Re-training After IRQ HPD Pulse
>             Due to Loss of Symbol Lock: HBR2 Extension
> (400.3.2.2) Successful Link Re-training After IRQ HPD Pulse Due
>             to Loss of Clock Recovery Lock: HBR2 Extension
> (400.3.2.3) Successful Link Re-training After IRQ HPD Pulse Due
>             to Loss of Inter-lane Alignment Lock: HBR2 Extension
>
> So far, DRM DP driver just read back the link status from 202h
> to 207h. DPR-120 would judge source can't pass these cases and
> shows below error messages.
>
> "Test FAILED, Source DUT does not read DPCD registers 200h-205h
> within 100 ms".

Acked-by: Jani Nikula <jani.nikula at intel.com>

for making the test pass iff everything else seems to work.

The underlying question is, though, should we look at 0x200-0x201 for
some status we don't look at?


>
> v2: Use sizeof() to retrieve array size.
>
> Cc: Jani Nikula <jani.nikula at intel.com>
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Lyude Paul <lyude at redhat.com>
> Cc: Simon Ser <contact at emersion.fr>
> Cc: Cooper Chiou <cooper.chiou at intel.com>
> Cc: William Tseng <william.tseng at intel.com>
> Signed-off-by: Lee Shawn C <shawn.c.lee at intel.com>
> ---
>  drivers/gpu/drm/drm_dp_helper.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_helper.c b/drivers/gpu/drm/drm_dp_helper.c
> index 24bbc710c825..4f03df317d62 100644
> --- a/drivers/gpu/drm/drm_dp_helper.c
> +++ b/drivers/gpu/drm/drm_dp_helper.c
> @@ -410,17 +410,19 @@ int drm_dp_dpcd_read_phy_link_status(struct drm_dp_aux *aux,
>  				     u8 link_status[DP_LINK_STATUS_SIZE])
>  {
>  	int ret;
> +	u8 full_link_stat[DP_LINK_STATUS_SIZE + 2];
>  
>  	if (dp_phy == DP_PHY_DPRX) {
>  		ret = drm_dp_dpcd_read(aux,
> -				       DP_LANE0_1_STATUS,
> -				       link_status,
> -				       DP_LINK_STATUS_SIZE);
> +				       DP_SINK_COUNT,
> +				       full_link_stat,
> +				       sizeof(full_link_stat));
>  
>  		if (ret < 0)
>  			return ret;
>  
> -		WARN_ON(ret != DP_LINK_STATUS_SIZE);
> +		memcpy(link_status, full_link_stat + 2, DP_LINK_STATUS_SIZE);
> +		WARN_ON(ret != DP_LINK_STATUS_SIZE + 2);
>  
>  		return 0;
>  	}

-- 
Jani Nikula, Intel Open Source Graphics Center