[alsa-devel] [PATCH] drm/i915: Enable VLV audio chicken bit for LPE audio

[Ville Syrjälä]

On Fri, Feb 03, 2017 at 02:32:37PM +0100, Takashi Iwai wrote:
> On Thu, 02 Feb 2017 11:12:53 +0100,
> Takashi Iwai wrote:
> > 
> > The audio chicken bit (register offset 0x62f38) seems required to make
> > DP audio working on some machines.  At least, on Dell Wyse 3040, I
> > failed to get the audio unless this bit is set once.
> > 
> > Strangely, the bit seems necessary only once, and it persists after
> > that, even some power-off cycles.  The register is supposedly
> > write-only, so it's no evidence whether the bit keeps effect
> > persistently.  But, judging from the experiment, it looks enough to
> > set it up once at the device initialization.
> > 
> > The patch is basically a cut from the original patch by Pierre-Louis
> > Bossart.
> > 
> > Cc: Pierre-Louis Bossart <pierre-louis.bossart at linux.intel.com>
> > Signed-off-by: Takashi Iwai <tiwai at suse.de>
> 
> I gave a typo to intel-gfx ML address, now corrected, sorry.
> 
> Are you i915 guys OK with this change?  I'd love to fix it for 4.11 in
> time, so please check and give ACK.
> 
> 
> thanks,
> 
> Takashi
> 
> > ---
> >  drivers/gpu/drm/i915/i915_reg.h        | 3 +++
> >  drivers/gpu/drm/i915/intel_lpe_audio.c | 7 +++++++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
> > index 4e24ba0cdbe8..4f15a3dc6d98 100644
> > --- a/drivers/gpu/drm/i915/i915_reg.h
> > +++ b/drivers/gpu/drm/i915/i915_reg.h
> > @@ -2062,6 +2062,9 @@ enum skl_disp_power_wells {
> >  #define I915_HDMI_LPE_AUDIO_SIZE	0x1000
> >  
> >  /* DisplayPort Audio w/ LPE */
> > +#define VLV_AUD_CHICKEN_BIT_REG		_MMIO(VLV_DISPLAY_BASE + 0x62F38)
> > +#define VLV_CHICKEN_BIT_DBG_ENABLE	(1 << 0)
> > +
> >  #define _VLV_AUD_PORT_EN_B_DBG		(VLV_DISPLAY_BASE + 0x62F20)
> >  #define _VLV_AUD_PORT_EN_C_DBG		(VLV_DISPLAY_BASE + 0x62F30)
> >  #define _VLV_AUD_PORT_EN_D_DBG		(VLV_DISPLAY_BASE + 0x62F34)
> > diff --git a/drivers/gpu/drm/i915/intel_lpe_audio.c b/drivers/gpu/drm/i915/intel_lpe_audio.c
> > index d3ffe0012692..3ba2799e93bd 100644
> > --- a/drivers/gpu/drm/i915/intel_lpe_audio.c
> > +++ b/drivers/gpu/drm/i915/intel_lpe_audio.c
> > @@ -248,6 +248,13 @@ static int lpe_audio_setup(struct drm_i915_private *dev_priv)
> >  		goto err_free_irq;
> >  	}
> >  
> > +	/* enable chicken bit; at least this is required for Dell Wyse 3040
> > +	 * with DP outputs (but only sometimes by some reason!)
> > +	 */
> > +	I915_WRITE(VLV_AUD_CHICKEN_BIT_REG,
> > +		   I915_READ(VLV_AUD_CHICKEN_BIT_REG) |
> > +		   VLV_CHICKEN_BIT_DBG_ENABLE);

RMW seems a little pointless since you verified that the register can't
actually be read.

So, with the read dropped
Reviewed-by: Ville Syrjälä <ville.syrjala at linux.intel.com>

> > +
> >  	return 0;
> >  err_free_irq:
> >  	irq_free_desc(dev_priv->lpe_audio.irq);
> > -- 
> > 2.11.0
> > 

-- 
Ville Syrjälä
Intel OTC