Re: [PATCH 5/6] drm/i915: enable scrambling

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

On Thu, Feb 02, 2017 at 11:23:19AM +0530, Sharma, Shashank wrote:
> Regards
> 
> Shashank
> 
> 
> On 2/1/2017 10:06 PM, Ville Syrjälä wrote:
> > On Wed, Feb 01, 2017 at 06:14:40PM +0530, Shashank Sharma wrote:
> >> Geminilake platform has a native HDMI 2.0 controller, and is
> >> capable of driving pixel-clocks upto 594Mhz. HDMI 2.0 spec
> >> mendates scrambling for these higher clocks, for reduced RF footprint.
> >>
> >> This patch checks if the monitor supports scrambling, and if required,
> >> enables it during the modeset.
> >>
> >> Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
> >> ---
> >>   drivers/gpu/drm/i915/i915_reg.h   |  2 ++
> >>   drivers/gpu/drm/i915/intel_ddi.c  |  5 +++++
> >>   drivers/gpu/drm/i915/intel_drv.h  |  2 ++
> >>   drivers/gpu/drm/i915/intel_hdmi.c | 42 +++++++++++++++++++++++++++++++++++++++
> >>   4 files changed, 51 insertions(+)
> >>
> >> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> >> index 495b789..cc85892 100644
> >> --- a/drivers/gpu/drm/i915/i915_reg.h
> >> +++ b/drivers/gpu/drm/i915/i915_reg.h
> >> @@ -7807,6 +7807,8 @@ enum {
> >>   #define  TRANS_DDI_EDP_INPUT_C_ONOFF	(6<<12)
> >>   #define  TRANS_DDI_DP_VC_PAYLOAD_ALLOC	(1<<8)
> >>   #define  TRANS_DDI_BFI_ENABLE		(1<<4)
> >> +#define  TRANS_DDI_HIGH_TMDS_CHAR_RATE	(1<<4)
> >> +#define  TRANS_DDI_HDMI_SCRAMBLING	(1<<0)
> >>   
> >>   /* DisplayPort Transport Control */
> >>   #define _DP_TP_CTL_A			0x64040
> >> diff --git a/drivers/gpu/drm/i915/intel_ddi.c b/drivers/gpu/drm/i915/intel_ddi.c
> >> index 9a9a670..aea81ce 100644
> >> --- a/drivers/gpu/drm/i915/intel_ddi.c
> >> +++ b/drivers/gpu/drm/i915/intel_ddi.c
> >> @@ -1278,6 +1278,11 @@ void intel_ddi_enable_transcoder_func(struct drm_crtc *crtc)
> >>   			temp |= TRANS_DDI_MODE_SELECT_HDMI;
> >>   		else
> >>   			temp |= TRANS_DDI_MODE_SELECT_DVI;
> >> +
> >> +		if (IS_GEMINILAKE(dev_priv)) {
> >> +			temp |= intel_hdmi_check_scrambling(intel_encoder,
> >> +				&intel_crtc->config->base.adjusted_mode);
> >> +		}
> >>   	} else if (type == INTEL_OUTPUT_ANALOG) {
> >>   		temp |= TRANS_DDI_MODE_SELECT_FDI;
> >>   		temp |= (intel_crtc->config->fdi_lanes - 1) << 1;
> >> diff --git a/drivers/gpu/drm/i915/intel_drv.h b/drivers/gpu/drm/i915/intel_drv.h
> >> index 393f243..aafce7f 100644
> >> --- a/drivers/gpu/drm/i915/intel_drv.h
> >> +++ b/drivers/gpu/drm/i915/intel_drv.h
> >> @@ -1588,6 +1588,8 @@ void intel_hdmi_init_connector(struct intel_digital_port *intel_dig_port,
> >>   bool intel_hdmi_compute_config(struct intel_encoder *encoder,
> >>   			       struct intel_crtc_state *pipe_config,
> >>   			       struct drm_connector_state *conn_state);
> >> +uint32_t intel_hdmi_check_scrambling(struct intel_encoder *intel_encoder,
> >> +				struct drm_display_mode *mode);
> >>   void intel_dp_dual_mode_set_tmds_output(struct intel_hdmi *hdmi, bool enable);
> >>   
> >>   
> >> diff --git a/drivers/gpu/drm/i915/intel_hdmi.c b/drivers/gpu/drm/i915/intel_hdmi.c
> >> index ebae2bd..92dd9bc 100644
> >> --- a/drivers/gpu/drm/i915/intel_hdmi.c
> >> +++ b/drivers/gpu/drm/i915/intel_hdmi.c
> >> @@ -1795,6 +1795,48 @@ static void intel_hdmi_destroy(struct drm_connector *connector)
> >>   	intel_hdmi->aspect_ratio = HDMI_PICTURE_ASPECT_NONE;
> >>   }
> >>   
> >> +static void
> >> +intel_hdmi_enable_scrambling(struct drm_connector *connector)
> >> +{
> >> +	struct drm_i915_private *dev_priv = connector->dev->dev_private;
> >> +	struct intel_hdmi *intel_hdmi = intel_attached_hdmi(connector);
> >> +	struct i2c_adapter *adapter =
> >> +			intel_gmbus_get_adapter(dev_priv, intel_hdmi->ddc_bus);
> >> +
> >> +	if (!drm_enable_scrambling(connector, adapter, true))
> >> +		DRM_ERROR("Request to enable scrambling failed\n");
> >> +}
> > I don't like hiding this somewhere deep like this. It should be
> > somewhere much higher up.
> Why ? All we need to do here is enable two bits in transcoder control 
> register, which is already being
> programmed in a calling function, so I dont see the use case, but I 
> might be missing some bigger picture.
> Can you please elaborate on this ?

We're talking to the display here, which is rather surprising to happen
from a function thing that on the first glance doesn't even seem to
touch the hardware.

> >
> > And I'm thinkign we might want to track the scrambler state
> > in the crtc state.
> Yes, that's a pretty good way to track dynamic status of scrambler, do 
> you think we should add this in
> drm_crtc_state itself ?

I'd just start with intel specific state and later we can see what
everyone else wants to do and potentially unify a bit.

> 
> - Shashank
> >> +
> >> +uint32_t intel_hdmi_check_scrambling(struct intel_encoder *intel_encoder,
> >> +				struct drm_display_mode *mode)
> >> +{
> >> +	struct intel_hdmi *intel_hdmi = enc_to_intel_hdmi(&intel_encoder->base);
> >> +	struct drm_connector *connector = &intel_hdmi->attached_connector->base;
> >> +	struct drm_hdmi_info *hdmi_info = &connector->display_info.hdmi_info;
> >> +	uint32_t hdmi_config = 0;
> >> +
> >> +	DRM_DEBUG_KMS("Checking scrambling for enc:%s connector:%s\n",
> >> +			intel_encoder->base.name, connector->name);
> >> +
> >> +	if (mode->clock < 340000) {
> >> +		if (hdmi_info->scr_info.low_clocks) {
> >> +			intel_hdmi_enable_scrambling(connector);
> >> +			hdmi_config |= TRANS_DDI_HDMI_SCRAMBLING;
> >> +		}
> >> +		return hdmi_config;
> >> +	}
> >> +
> >> +	/* Enable scrambling for clocks > 340M */
> >> +	if (hdmi_info->scr_info.supported) {
> >> +		intel_hdmi_enable_scrambling(connector);
> >> +		hdmi_config |= TRANS_DDI_HDMI_SCRAMBLING;
> >> +	}
> >> +
> >> +	/* Scrambling or not, if clock > 340M, set high char rate */
> >> +	hdmi_config |= TRANS_DDI_HIGH_TMDS_CHAR_RATE;
> >> +	return hdmi_config;
> >> +}
> >> +
> >>   static u8 intel_hdmi_ddc_pin(struct drm_i915_private *dev_priv,
> >>   			     enum port port)
> >>   {
> >> -- 
> >> 1.9.1

-- 
Ville Syrjälä
Intel OTC
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