Re: [PATCH v5 2/4] drm/i915: implement sync_audio_rate callback

[Takashi Iwai <tiwai@suse.de>]

On Mon, 24 Aug 2015 14:53:19 +0200,
Ville Syrjälä wrote:
> 
> On Mon, Aug 24, 2015 at 02:38:14AM +0000, Yang, Libin wrote:
> > > -----Original Message-----
> > > From: Ville Syrjälä [mailto:ville.syrjala@linux.intel.com]
> > > Sent: Friday, August 21, 2015 11:14 PM
> > > To: Yang, Libin
> > > Cc: alsa-devel@alsa-project.org; tiwai@suse.de; intel-
> > > gfx@lists.freedesktop.org; daniel.vetter@ffwll.ch;
> > > jani.nikula@linux.intel.com
> > > Subject: Re: [Intel-gfx] [PATCH v5 2/4] drm/i915: implement
> > > sync_audio_rate callback
> > > 
> > > On Tue, Aug 18, 2015 at 02:51:52PM +0800, libin.yang@intel.com
> > > wrote:
> > > > From: Libin Yang <libin.yang@intel.com>
> > > >
> > > > HDMI audio may not work at some frequencies
> > > > with the HW provided N/CTS.
> > > >
> > > > This patch sets the proper N value for the
> > > > given audio sample rate at the impacted frequencies.
> > > > At other frequencies, it will use the N/CTS value
> > > > which HW provides.
> > > >
> > > > Signed-off-by: Libin Yang <libin.yang@intel.com>
> > > > ---
> > > >  drivers/gpu/drm/i915/intel_audio.c | 119
> > > +++++++++++++++++++++++++++++++++++++
> > > >  1 file changed, 119 insertions(+)
> > > >
> > > > diff --git a/drivers/gpu/drm/i915/intel_audio.c
> > > b/drivers/gpu/drm/i915/intel_audio.c
> > > > index dc32cf4..96b97be 100644
> > > > --- a/drivers/gpu/drm/i915/intel_audio.c
> > > > +++ b/drivers/gpu/drm/i915/intel_audio.c
> > > > @@ -68,6 +68,31 @@ static const struct {
> > > >  	{ 148500, AUD_CONFIG_PIXEL_CLOCK_HDMI_148500 },
> > > >  };
> > > >
> > > > +/* HDMI N/CTS table */
> > > > +#define TMDS_297M 297000
> > > > +#define TMDS_296M DIV_ROUND_UP(297000 * 1000, 1001)
> > > 
> > > I don't really like the defines.
> > 
> > I agree it's not a good name. Do you have some suggestions?
> 
> I'd probably just have used raw numbers myself.

It's quite unsafe.  You can easily overlook, e.g. 29700 instead of
297000.


Takashi
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