Re: [PATCH v4 1/2] drm/i915/dp: Enable DP audio stall fix for gen9 platforms

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

On Wed, 26 Oct 2016, "Pandiyan, Dhinakaran" <dhinakaran.pandiyan@intel.com> wrote:
> On Wed, 2016-10-26 at 11:57 +0300, Jani Nikula wrote:
>> On Wed, 26 Oct 2016, Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com> wrote:
>> > Enabling DP audio stall fix is necessary to play audio over DP HBR2. So,
>> > let's set this bit right before enabling the audio codec. Playing audio
>> > without setting this bit results in pipe FIFO underruns.
>> >
>> > This workaround is applicable only for audio sample rates up to 96kHz. For
>> > frequencies above 96kHz, this is insufficient and cdclk should be increased
>> > to at least 432 MHz, just like BDW. Since, the audio driver does not
>> > support sample rates > 48 kHz, we are safe with this fix for now.
>> >
>> > v2: Inlined the code change within hsw_audio_codec_enable() (Jani)
>> >     Fixed the port clock typo
>> >     Added TODO comment
>> > Signed-off-by: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/i915_reg.h    |  5 +++++
>> >  drivers/gpu/drm/i915/intel_audio.c | 30 +++++++++++++++++++++++++++++-
>> >  2 files changed, 34 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>> > index 00efaa1..76dac48 100644
>> > --- a/drivers/gpu/drm/i915/i915_reg.h
>> > +++ b/drivers/gpu/drm/i915/i915_reg.h
>> > @@ -6236,6 +6236,11 @@ enum {
>> >  #define SLICE_ECO_CHICKEN0			_MMIO(0x7308)
>> >  #define   PIXEL_MASK_CAMMING_DISABLE		(1 << 14)
>> >  
>> > +#define _CHICKEN_TRANS_A	0x420C0
>> > +#define _CHICKEN_TRANS_B	0x420C4
>> > +#define CHICKEN_TRANS(tran) _MMIO_TRANS(tran, _CHICKEN_TRANS_A, _CHICKEN_TRANS_B)
>> > +#define SPARE_13	(1<<13)
>> > +
>> >  /* WaCatErrorRejectionIssue */
>> >  #define GEN7_SQ_CHICKEN_MBCUNIT_CONFIG		_MMIO(0x9030)
>> >  #define  GEN7_SQ_CHICKEN_MBCUNIT_SQINTMOB	(1<<11)
>> > diff --git a/drivers/gpu/drm/i915/intel_audio.c b/drivers/gpu/drm/i915/intel_audio.c
>> > index 7093cfb..894f11e 100644
>> > --- a/drivers/gpu/drm/i915/intel_audio.c
>> > +++ b/drivers/gpu/drm/i915/intel_audio.c
>> > @@ -283,6 +283,8 @@ static void hsw_audio_codec_disable(struct intel_encoder *encoder)
>> >  {
>> >  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
>> >  	struct intel_crtc *intel_crtc = to_intel_crtc(encoder->base.crtc);
>> > +	struct intel_crtc_state *crtc_config =  intel_crtc->config;
>> > +	enum transcoder cpu_transcoder = crtc_config->cpu_transcoder;
>> >  	enum pipe pipe = intel_crtc->pipe;
>> >  	uint32_t tmp;
>> >  
>> > @@ -290,13 +292,21 @@ static void hsw_audio_codec_disable(struct intel_encoder *encoder)
>> >  
>> >  	mutex_lock(&dev_priv->av_mutex);
>> >  
>> > +	/*Disable DP audio stall fix for HBR2*/
>> 
>> Nitpick, spaces after /* and before */.
>> 
>> > +	if (IS_GEN9(dev_priv) && intel_crtc_has_dp_encoder(crtc_config) &&
>> > +	    crtc_config->port_clock >= 540000) {
>> > +		tmp = I915_READ(CHICKEN_TRANS(cpu_transcoder));
>> > +		tmp &= ~SPARE_13;
>> > +		I915_WRITE(CHICKEN_TRANS(cpu_transcoder), tmp);
>> > +	}
>> 
>> Hmm. Why don't we just do this unconditionally?
>> 
>
> That bit is disabled by default, so avoiding  two MMIO ops. that are not
> required.

That makes no difference on the modeset path.

>
>> > +
>> >  	/* Disable timestamps */
>> >  	tmp = I915_READ(HSW_AUD_CFG(pipe));
>> >  	tmp &= ~AUD_CONFIG_N_VALUE_INDEX;
>> >  	tmp |= AUD_CONFIG_N_PROG_ENABLE;
>> >  	tmp &= ~AUD_CONFIG_UPPER_N_MASK;
>> >  	tmp &= ~AUD_CONFIG_LOWER_N_MASK;
>> > -	if (intel_crtc_has_dp_encoder(intel_crtc->config))
>> > +	if (intel_crtc_has_dp_encoder(crtc_config))
>> >  		tmp |= AUD_CONFIG_N_VALUE_INDEX;
>> >  	I915_WRITE(HSW_AUD_CFG(pipe), tmp);
>> >  
>> > @@ -315,6 +325,8 @@ static void hsw_audio_codec_enable(struct drm_connector *connector,
>> >  {
>> >  	struct drm_i915_private *dev_priv = to_i915(connector->dev);
>> >  	struct intel_crtc *intel_crtc = to_intel_crtc(intel_encoder->base.crtc);
>> > +	struct intel_crtc_state *crtc_config =  intel_crtc->config;
>> > +	enum transcoder cpu_transcoder = crtc_config->cpu_transcoder;
>> >  	enum pipe pipe = intel_crtc->pipe;
>> >  	enum port port = intel_encoder->port;
>> >  	const uint8_t *eld = connector->eld;
>> > @@ -326,6 +338,22 @@ static void hsw_audio_codec_enable(struct drm_connector *connector,
>> >  
>> >  	mutex_lock(&dev_priv->av_mutex);
>> >  
>> > +	/* Enable DP audio stall fix for HBR2
>> > +	 *
>> > +	 * TODO: This workaround is applicable only for audio sample rates up
>> > +	 * to 96kHz. For frequencies above 96kHz, this is insufficient and
>> > +	 * cdclk should be increased to at least 432 MHz, just like BDW. Since,
>> > +	 * the audio driver does not support sample rates > 48 kHz, we are safe
>> > +	 * with this fix for now.
>> > +	 */
>> 
>> Is this TODO required if you already have that check in patch 2/2?
>> 
>
> In fact, this patch itself is not required if we are increasing the
> cdclk to 432 MHz for gen9 platforms (like patch 2/2). Having this
> workaround gives us the option running the pipeline at a lower cdclk
> frequency i.e., 337.5 MHz, which I believe should be better in terms of
> power.

The conditions for requiring higher cdclk are different in patch 2/2,
right? That one also requires 4 lanes. So with 1 or 2 lanes this is
still needed.

BR,
Jani.


>
>
>> > +
>> > +	if (IS_GEN9(dev_priv) && intel_crtc_has_dp_encoder(crtc_config) &&
>> > +	    crtc_config->port_clock >= 540000) {
>> > +		tmp = I915_READ(CHICKEN_TRANS(cpu_transcoder));
>> > +		tmp |= SPARE_13;
>> > +		I915_WRITE(CHICKEN_TRANS(cpu_transcoder), tmp);
>> > +	}
>> > +
>> >  	/* Enable audio presence detect, invalidate ELD */
>> >  	tmp = I915_READ(HSW_AUD_PIN_ELD_CP_VLD);
>> >  	tmp |= AUDIO_OUTPUT_ENABLE(pipe);
>> 
>

-- 
Jani Nikula, Intel Open Source Technology Center
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