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

[Takashi Iwai]

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