[alsa-devel] [PATCH V2 1/1] audio: Fix playback noise with 24/32 bit sample size on BXT

[Takashi Iwai]

On Mon, 07 Dec 2015 08:59:13 +0100,
han.lu at intel.com wrote:
> 
> From: "Lu, Han" <han.lu at intel.com>
> 
> In BXT-P A0, HD-Audio DMA requests is later than expected,
> and makes an audio stream sensitive to system latencies when
> 24/32 bits are playing.
> Adjusting threshold of DMA fifo to force the DMA request
> sooner to improve latency tolerance at the expense of power.
> 
> v2: move Intel specific code to hda_intel.c
> 
> Signed-off-by: Lu, Han <han.lu at intel.com>

Applied, thanks.


Takashi

> 
> diff --git a/include/sound/hda_register.h b/include/sound/hda_register.h
> index 2ae8812..94dc6a9 100644
> --- a/include/sound/hda_register.h
> +++ b/include/sound/hda_register.h
> @@ -93,6 +93,9 @@ enum { SDI0, SDI1, SDI2, SDI3, SDO0, SDO1, SDO2, SDO3 };
>  #define AZX_REG_HSW_EM4			0x100c
>  #define AZX_REG_HSW_EM5			0x1010
>  
> +/* Skylake/Broxton display HD-A controller Extended Mode registers */
> +#define AZX_REG_SKL_EM4L		0x1040
> +
>  /* PCI space */
>  #define AZX_PCIREG_TCSEL		0x44
>  
> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
> index 963f824..bff5c8b 100644
> --- a/sound/pci/hda/hda_intel.c
> +++ b/sound/pci/hda/hda_intel.c
> @@ -355,6 +355,8 @@ enum {
>  					((pci)->device == 0x0d0c) || \
>  					((pci)->device == 0x160c))
>  
> +#define IS_BROXTON(pci)	((pci)->device == 0x5a98)
> +
>  static char *driver_short_names[] = {
>  	[AZX_DRIVER_ICH] = "HDA Intel",
>  	[AZX_DRIVER_PCH] = "HDA Intel PCH",
> @@ -506,15 +508,36 @@ static void azx_init_pci(struct azx *chip)
>          }
>  }
>  
> +/*
> + * In BXT-P A0, HD-Audio DMA requests is later than expected,
> + * and makes an audio stream sensitive to system latencies when
> + * 24/32 bits are playing.
> + * Adjusting threshold of DMA fifo to force the DMA request
> + * sooner to improve latency tolerance at the expense of power.
> + */
> +static void bxt_reduce_dma_latency(struct azx *chip)
> +{
> +	u32 val;
> +
> +	val = azx_readl(chip, SKL_EM4L);
> +	val &= (0x3 << 20);
> +	azx_writel(chip, SKL_EM4L, val);
> +}
> +
>  static void hda_intel_init_chip(struct azx *chip, bool full_reset)
>  {
>  	struct hdac_bus *bus = azx_bus(chip);
> +	struct pci_dev *pci = chip->pci;
>  
>  	if (chip->driver_caps & AZX_DCAPS_I915_POWERWELL)
>  		snd_hdac_set_codec_wakeup(bus, true);
>  	azx_init_chip(chip, full_reset);
>  	if (chip->driver_caps & AZX_DCAPS_I915_POWERWELL)
>  		snd_hdac_set_codec_wakeup(bus, false);
> +
> +	/* reduce dma latency to avoid noise */
> +	if (IS_BROXTON(pci))
> +		bxt_reduce_dma_latency(chip);
>  }
>  
>  /* calculate runtime delay from LPIB */
> -- 
> 2.5.0
>