Re: [PATCH 10/10] drm/i915/cnl: Fix DP max rate for Cannonlake with port F.

From: Rodrigo Vivi <rodrigo.vivi@intel.com>
To: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org,
	Lucas De Marchi <lucas.demarchi@intel.com>
Subject: Re: [PATCH 10/10] drm/i915/cnl: Fix DP max rate for Cannonlake with port F.
Date: Tue, 30 Jan 2018 12:42:12 -0800	[thread overview]
Message-ID: <20180130204211.66d46of2aro4muij@intel.com> (raw)
In-Reply-To: <877erzaiyo.fsf@intel.com>

On Tue, Jan 30, 2018 at 07:45:03AM +0000, Jani Nikula wrote:
> On Mon, 29 Jan 2018, Rodrigo Vivi <rodrigo.vivi@intel.com> wrote:
> > On CNL SKUs that uses port F,  max DP rate is 8.1G for all
> > ports when we have the elevated voltage (higher than 0.85V).
> >
> > v2: Make commit message more generic.
> > v3: Move conditions to a helper to get easier to read. (Ville).
> > v4: Add a mention to the numerical voltage on commit
> >     message per Manasi request.
> > v5: Thanks CI! "error: control reaches end of non-void function"
> >
> > Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
> > Cc: Lucas De Marchi <lucas.demarchi@intel.com>
> > Cc: Manasi Navare <manasi.d.navare@intel.com>
> > Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> > Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
> > ---
> >  drivers/gpu/drm/i915/intel_dp.c | 31 ++++++++++++++++++++++++-------
> >  1 file changed, 24 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/i915/intel_dp.c b/drivers/gpu/drm/i915/intel_dp.c
> > index 86a5e8bfe2a6..1f10bdb855e7 100644
> > --- a/drivers/gpu/drm/i915/intel_dp.c
> > +++ b/drivers/gpu/drm/i915/intel_dp.c
> > @@ -220,15 +220,36 @@ intel_dp_downstream_max_dotclock(struct intel_dp *intel_dp)
> >  	return max_dotclk;
> >  }
> >  
> > +static int cnl_adjusted_max_rate(struct intel_dp *intel_dp, int size)
> > +{
> > +	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> > +	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> > +	enum port port = dig_port->base.port;
> > +
> > +	u32 voltage = I915_READ(CNL_PORT_COMP_DW3) & VOLTAGE_INFO_MASK;
> > +
> > +	/* Low voltage SKUs are limited to max of 5.4G */
> > +	if (voltage == VOLTAGE_INFO_0_85V)
> > +		return size - 2;
> > +
> > +	/* For this SKU 8.1G is supported in all ports */
> > +	if(IS_CNL_WITH_PORT_F(dev_priv))
> > +		return size;
> > +
> > +	/* For other SKUs, max rate on ports A and B is 5.4G */
> > +	if (port == PORT_A || port == PORT_D)
> > +		return size - 2;
> > +
> > +	return size;
> 

ops, I had missed this email. Since I had resent the series, the old one
was on top of my inbox.

> IMO this splits the ARRAY_SIZE() and the (size - 2) adjustments too
> much. They were tolerable within one function, but looking at this
> function alone, the (size - 2) is a big WTF.
> 
> I'd just put this all in the same function.

I just split per Ville request to make conditions more readable.
I now agree that size outside of the context get uglier.

What about changing:

int num_source_rates
const int *source_rates

into:
struct {
int num;
const int *list;
int max_available;
} source_rates;

So that function or whenever we need like reading from new VBT field
we set a max_available, and when going through the list for finding
the common rate instead of relying only on num we also check max_available?

Agree?
Thoughts?

> 
> BR,
> Jani.
> 
> 
> > +}
> > +
> >  static void
> >  intel_dp_set_source_rates(struct intel_dp *intel_dp)
> >  {
> >  	struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> >  	struct drm_i915_private *dev_priv = to_i915(dig_port->base.base.dev);
> > -	enum port port = dig_port->base.port;
> >  	const int *source_rates;
> >  	int size;
> > -	u32 voltage;
> >  
> >  	/* This should only be done once */
> >  	WARN_ON(intel_dp->source_rates || intel_dp->num_source_rates);
> > @@ -238,11 +259,7 @@ intel_dp_set_source_rates(struct intel_dp *intel_dp)
> >  		size = ARRAY_SIZE(bxt_rates);
> >  	} else if (IS_CANNONLAKE(dev_priv)) {
> >  		source_rates = cnl_rates;
> > -		size = ARRAY_SIZE(cnl_rates);
> > -		voltage = I915_READ(CNL_PORT_COMP_DW3) & VOLTAGE_INFO_MASK;
> > -		if (port == PORT_A || port == PORT_D ||
> > -		    voltage == VOLTAGE_INFO_0_85V)
> > -			size -= 2;
> > +		size = cnl_adjusted_max_rate(intel_dp, ARRAY_SIZE(cnl_rates));
> >  	} else if (IS_GEN9_BC(dev_priv)) {
> >  		source_rates = skl_rates;
> >  		size = ARRAY_SIZE(skl_rates);
> 
> -- 
> Jani Nikula, Intel Open Source Technology Center
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