Re: [Intel-gfx] [PATCH v4 2/2] drm/i915/dp: Helper to check for DDI BUF status to get active

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Fri, Jun 26, 2020 at 04:26:41PM -0700, Manasi Navare wrote:
> Based on the platform, Bspec expects us to wait or poll with
> timeout for DDI BUF IDLE bit to be set to 0 (non idle) or get active
> after enabling DDI_BUF_CTL.
> 
> v4:
> * Use the timeout for GLK (Ville)
> v3:
> * Add a new function _active for DDI BUF CTL to be non idle (Ville)
> v2:
> * Based on platform, fixed delay or poll (Ville)
> * Use a helper to do this (Imre, Ville)
> 
> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> Cc: Imre Deak <imre.deak@intel.com>
> Signed-off-by: Manasi Navare <manasi.d.navare@intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_ddi.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_ddi.c b/drivers/gpu/drm/i915/display/intel_ddi.c
> index 052a74625a61..94d57b57139b 100644
> --- a/drivers/gpu/drm/i915/display/intel_ddi.c
> +++ b/drivers/gpu/drm/i915/display/intel_ddi.c
> @@ -1195,6 +1195,20 @@ static void intel_wait_ddi_buf_idle(struct drm_i915_private *dev_priv,
>  			port_name(port));
>  }
>  
> +static void intel_wait_ddi_buf_active(struct drm_i915_private *dev_priv,
> +				      enum port port)
> +{
> +	if (INTEL_GEN(dev_priv) < 10 && !IS_GEMINILAKE(dev_priv) ) {
> +		usleep_range(600, 1000);

I would probably put a spec quote here to make it clear what this is:
"Wait >518 us for buffers to enable..."

Or we could s/600/518/ to make it easier to figure out. But that could
be a followup.

> +		return;
> +	}
> +
> +	if (wait_for_us(!(intel_de_read(dev_priv, DDI_BUF_CTL(port)) &
> +			  DDI_BUF_IS_IDLE), 600))

Spec says 500 usec for this. Is there a reason to not go with the spec
value? I guess one argument is that we didn't do it before. But I'd
probably change it, if not in this patch then as a followup.

> +		drm_err(&dev_priv->drm, "Timeout waiting for DDI BUF %c to get active\n",
> +			port_name(port));
> +}
> +
>  static u32 hsw_pll_to_ddi_pll_sel(const struct intel_shared_dpll *pll)
>  {
>  	switch (pll->info->id) {
> @@ -4020,7 +4034,7 @@ static void intel_ddi_prepare_link_retrain(struct intel_dp *intel_dp)
>  	intel_de_write(dev_priv, DDI_BUF_CTL(port), intel_dp->DP);
>  	intel_de_posting_read(dev_priv, DDI_BUF_CTL(port));
>  
> -	udelay(600);
> +	intel_wait_ddi_buf_active(dev_priv, port);

Still can't see fdi anywhere.

Whatever
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

>  }
>  
>  static void intel_ddi_set_link_train(struct intel_dp *intel_dp,
> -- 
> 2.19.1

-- 
Ville Syrjälä
Intel
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