Re: [PATCH] drm/i915: Enable VLV audio chicken bit for LPE audio

[Takashi Iwai <tiwai@suse.de>]

On Fri, 03 Feb 2017 15:54:33 +0100,
Ville Syrjälä wrote:
> 
> 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@linux.intel.com>
> > > Signed-off-by: Takashi Iwai <tiwai@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.

Indeed.

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

Thanks!


Takashi
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