[alsa-devel] HDA: Enable chipset gcap usage

[Tobin Davis]

On Tue, 2008-01-08 at 08:11 +0100, Takashi Iwai wrote:

> At Mon, 07 Jan 2008 10:00:20 -0800,
> Tobin Davis wrote:
> > 
> > On Mon, 2008-01-07 at 11:59 +0100, Takashi Iwai wrote:
> > 
> >     At Thu, 03 Jan 2008 15:34:05 -0800,
> >     Tobin Davis wrote:
> >     > 
> >     > Summary:  hda_intel.c use gcap register to determine number of streams
> >     > supported by southbridge.
> >     > 
> >     > This patch removes hardcoded values for the number of streams supported
> >     > by the southbridge in most chipsets, and reads these values from the
> >     > chipset directly.  Most systems are hardwired for 4 streams in each
> >     > direction, but newer chipsets change that capability.
> >     > 
> >     > 
> >     > Signed off by Tobin Davis <tdavis at dsl-only.net>
> >     > [2 hda-gcap.patch <text/x-patch; UTF-8 (7bit)>]
> >     > diff -r 1227a1c12325 pci/hda/hda_intel.c
> >     > --- a/pci/hda/hda_intel.c     Mon Dec 24 14:40:56 2007 +0100
> >     > +++ b/pci/hda/hda_intel.c     Thu Jan 03 15:27:10 2008 -0800
> >     > @@ -1709,12 +1709,13 @@ static int __devinit azx_create(struct s
> >     >  {
> >     >       struct azx *chip;
> >     >       int err;
> >     > +     unsigned short gcap;
> >     >       static struct snd_device_ops ops = {
> >     >               .dev_free = azx_dev_free,
> >     >       };
> >     >  
> >     >       *rchip = NULL;
> >     > -     
> >     > +
> >     >       err = pci_enable_device(pci);
> >     >       if (err < 0)
> >     >               return err;
> >     > @@ -1790,10 +1791,19 @@ static int __devinit azx_create(struct s
> >     >               chip->capture_index_offset = ATIHDMI_CAPTURE_INDEX;
> >     >               break;
> >     >       default:
> >     > -             chip->playback_streams = ICH6_NUM_PLAYBACK;
> >     > -             chip->capture_streams = ICH6_NUM_CAPTURE;
> >     > -             chip->playback_index_offset = ICH6_PLAYBACK_INDEX;
> >     > -             chip->capture_index_offset = ICH6_CAPTURE_INDEX;
> >     > +             /* read number of streams from GCAP register instead of using
> >     > +              * hardcoded value
> >     > +              */
> >     > +             gcap = azx_readw(chip, GCAP);
> >     > +             if(!gcap) {
> >     > +                     snd_printk(KERN_ERR "Device has no streams \n");
> >     > +                     goto errout;
> >     > +             };
> >     
> >     I think it's safer to assign old ICH6_* values in this case (just to
> >     be sure) after a warning message.
> > 
> > Actually, this should never have been hardcoded in the first place.  The HDA
> > PRM (April 2005) states that the value returned is hardwired to 4 streams in
> > the ICH6/7 southbridge of the Intel chipset.  By hardcoding the values in the
> > driver, we don't allow changes to future (hint - real soon) chipsets.  This
> > just cleans up this bit of code that has been around since this code was
> > created.  If I had the other systems in the case statement to test, I'm sure
> > we could do away with the case statement entirely, just by reading the values
> > instead of second guessing them.  If the chipsets follow the spec, this method
> > should work all around.
> 
> Well, I wasn't clear about the comment above.  I meant the constant
> values can be used as fallbacks in case these values can't be read,
> instead of returning error and quit.  This would avoid regressions, at
> least.
> 
> 
> >     > +             chip->playback_streams = (gcap&(0xF<<12))>>12;
> >     > +             chip->capture_streams = (gcap&(0xF<<8))>>8;
> >     > +             chip->playback_index_offset = (gcap&(0xF<<12))>>12;
> >     > +             chip->capture_index_offset = 0;
> >     
> > I'm not entirely convinced of this method for the index_offsets, but it works
> > on tested systems here.  I'll review the PRM for more guidance.
> 
> It should be fine as is.  A stream can be assigned freely  regardless
> the I/O direction on ICH (and others too).  So, basically it's always:
> 
> 	capture_index_offset = 0;
> 	playback_index_offset = capture_streams;


This isn't entirely true, at least based on the ATIHDMI code in the
previous case statement.  It would be interesting to see what GCAP
returns for the two cases (ATIHDMI, and ULI).  If they could be used by
this, we could do away with the switch entirely (except maybe as a
fallback).




> 
> So, the above would be a bit more readable like below:
> 
> 	chip->capture_streams = (gcap >> 8) & 0x0f;
> 	chip->playback_streams = (gcap >> 12) & 0x0f;
> 	chip->capture_index_offset = 0;
> 	chip->playback_index_offset = chip->capture_streams;
> 
> >     > +
> >     >               break;
> >     >       }
> >     >       chip->num_streams = chip->playback_streams + chip->capture_streams;
> >     
> >     The patch has some coding style issues, for example, no space around
> >     operators, etc.  Try to run $LINUX/scripts/checkpatch.pl, fix the
> >     errors and the issue above, and please repost the patch again.
> >     
> > This must be a new script in the kernel.  My development system (2.6.17)
> > doesn't have it, but it is on my laptop (2.6.22).  I ran it, ant it reported
> > one error " if(!gcap) " which I fixed.  I also added some spacing around the
> > bit manipulation code for streams and offsets. 
> 
> You should try checkpatch.pl included in the very latest linux kernel.
> The script itself has been improved (and became less annoying).



We should be getting Ubuntu Hardy based code at work soon.  I'll look at
it then.  Right now I'm way overloaded with this stupid java programming
class (instructor hasn't helped the class so they have been relying on
me for help).


-- 
Tobin Davis  


Nobody wants constructive criticism.  It's all we can do to put up with
constructive praise.