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

[Takashi Iwai]

On Tue, 08 Dec 2015 01:35:32 +0100,
Lu, Han wrote:
> 
> > -----Original Message-----
> > From: Takashi Iwai [mailto:tiwai at suse.de]
> > Sent: Monday, December 7, 2015 4:06 PM
> > To: Lu, Han
> > Cc: libin.yang at linux.intel.com; mengdong.lin at linux.intel.com;
> > han.lu at linux.intel.com; alsa-devel at alsa-project.org
> > Subject: Re: [PATCH V2 1/1] audio: Fix playback noise with 24/32 bit sample
> > size on BXT
> > 
> > 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
> > 
> 
> Thanks!
> 
> One more thing, I was tried to implement this patch by define a macro
> AZX_DCAPS_XXX instead of IS_BROXTON(pci), but it looks like no spare bit
> left. (bit 22 and bit 31 are reserved bits, right?) Is there a plan to extend the
> caps structure?

Currently not.  If the check is once-off and be in hda_intel.c,
extending DCAPS is too much.


thanks,

Takashi

> 
> BR,
> Han
> 
> > >
> > > 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
> > >
>