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

[Takashi Iwai]

On Mon, 07 Dec 2015 03:51:49 +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.
> 
> Signed-off-by: Lu, Han <han.lu at intel.com>

It's a wrong place to patch.  hda_controller.c is for generic
HD-audio.  The Intel-specific code should go into hda_intel.c.


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_controller.c b/sound/pci/hda/hda_controller.c
> index 22dbfa5..6c2aa4c 100644
> --- a/sound/pci/hda/hda_controller.c
> +++ b/sound/pci/hda/hda_controller.c
> @@ -27,6 +27,7 @@
>  #include <linux/module.h>
>  #include <linux/pm_runtime.h>
>  #include <linux/slab.h>
> +#include <linux/pci.h>
>  #include <sound/core.h>
>  #include <sound/initval.h>
>  #include "hda_controller.h"
> @@ -34,6 +35,8 @@
>  #define CREATE_TRACE_POINTS
>  #include "hda_controller_trace.h"
>  
> +#define is_broxton(pci)	((pci)->device == 0x5a98)
> +
>  /* DSP lock helpers */
>  #define dsp_lock(dev)		snd_hdac_dsp_lock(azx_stream(dev))
>  #define dsp_unlock(dev)		snd_hdac_dsp_unlock(azx_stream(dev))
> @@ -880,14 +883,35 @@ EXPORT_SYMBOL_GPL(snd_hda_codec_load_dsp_cleanup);
>  #endif /* CONFIG_SND_HDA_DSP_LOADER */
>  
>  /*
> + * 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);
> +}
> +
> +/*
>   * reset and start the controller registers
>   */
>  void azx_init_chip(struct azx *chip, bool full_reset)
>  {
> +	struct pci_dev *pci = chip->pci;
> +
>  	if (snd_hdac_bus_init_chip(azx_bus(chip), full_reset)) {
>  		/* correct RINTCNT for CXT */
>  		if (chip->driver_caps & AZX_DCAPS_CTX_WORKAROUND)
>  			azx_writew(chip, RINTCNT, 0xc0);
> +		/* reduce dma latency to avoid noise */
> +		if (is_broxton(pci))
> +			bxt_reduce_dma_latency(chip);
>  	}
>  }
>  EXPORT_SYMBOL_GPL(azx_init_chip);
> -- 
> 2.5.0
>