Re: [Intel-gfx] [RESEND PATCHv2 2/2] i915/display/dp: SDP CRC16 for 128b132b link layer

[Jani Nikula <jani.nikula@intel.com>]

On Tue, 14 Feb 2023, Arun R Murthy <arun.r.murthy@intel.com> wrote:
> Enable SDP error detection configuration, this will set CRC16 in
> 128b/132b link layer.
> For Display version 13 a hardware bit31 in register VIDEO_DIP_CTL is
> added to enable/disable SDP CRC applicable for DP2.0 only, but the
> default value of this bit will enable CRC16 in 128b/132b hence
> skipping this write.
> Corrective actions on SDP corruption is yet to be defined.
>
> v2: Moved the CRC enable to link training init(Jani N)
> v3: Moved crc enable to ddi pre enable <Jani N>
>
> Signed-off-by: Arun R Murthy <arun.r.murthy@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index 254559abedfb..fa995341614d 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -2330,6 +2330,18 @@ static void tgl_ddi_pre_enable_dp(struct intel_atomic_state *state,
>  				 crtc_state->port_clock,
>  				 crtc_state->lane_count);
>  
> +	/* DP v2.0 SCR on SDP CRC16 for 128b/132b Link Layer */
> +	if (intel_dp_is_uhbr(crtc_state))
> +		drm_dp_dpcd_writeb(&intel_dp->aux,
> +				   DP_SDP_ERROR_DETECTION_CONFIGURATION,
> +				   DP_SDP_CRC16_128B132B_EN);
> +		/*
> +		 * VIDEO_DIP_CTL register bit 31 should be set to '0' to not
> +		 * disable SDP CRC. This is applicable for Display version 13.
> +		 * Default value of bit 31 is '0' hence discarding the write
> +		 */
> +		/* TODO: Corrective actions on SDP corruption yet to be defined */
> +

So yeah, I told you to do this in this function. But look at the
surroundings, does it look like a direct drm_dp_dpcd_writeb() call fits
here?

tgl_ddi_pre_enable_dp() is a function that calls functions, and doesn't
bother with any details. No register or DPCD reads or writes.

Sure, it's a matter of style, and I hate to feel like I'm pushing you
around with this. But the above really needs to be in a separate
function when it's done in tgl_ddi_pre_enable_dp().

It'll also help with placing the comments. You can have *one* block
comment above the function with all the details, TODO notes and
everything, indented at the top level. (Above, the comments are indented
as if they were within a {} block.)

BR,
Jani.




>  	/*
>  	 * We only configure what the register value will be here.  Actual
>  	 * enabling happens during link training farther down.

-- 
Jani Nikula, Intel Open Source Graphics Center