[alsa-devel] [PATCH 2/3] ASoC: AC97: S3C: Add controller driver

jassi brar jassisinghbrar at gmail.com
Tue Jan 26 13:11:55 CET 2010

On Tue, Jan 26, 2010 at 8:52 PM, Mark Brown
<broonie at opensource.wolfsonmicro.com> wrote:
> On Tue, Jan 26, 2010 at 08:17:25PM +0900, jassi brar wrote:
>> On Tue, Jan 26, 2010 at 7:47 PM, Mark Brown
>> >> +     default:
>> >> +             s3c_ac97_cold_reset(ac97);
>> >> +             s3c_ac97_warm_reset(ac97);
>> >> +             break;
>> >> +     }
>> > This automatic cold and warm reset looks a bit fishy - obviously if this
>> > code path ever gets hit in normal operation then it's going to seriously
>> > disrupt things since it'll reset the CODEC registers.  A warm reset by
>> > itself wouldn't be a problem but I'd rather see explicit cold resets in
>> > the callers where that's required.
>> Before read/write we need to ensure the link is active. And to reach the
>> active state we have to do that as suggested by the FSM shown in SoCs' Manual.
> That's not addressing the problem, though - the big issue is not
> bringing up the AC97 link, it's the fact that you're doing an
> uncontrolled cold reset.  If we hit this code path it'll revert the
> device registers to default which will upset the drivers for the CODEC
> rather badly.  There should be no possibility of that happening, if it
> is happening it's something that callers really should know about.
It should never be reached after the link is up and running. Only if something
goes wrong at runtime, would the controller state be changed. And
this is an attempt to recover from that failure. If the upper layer should
know of such failure, then maybe we should not do it.
I have never seen such runtime error though.

>> Also, this helps not relying on codec/core to perform particular steps
>> of initializations.
> Equally well if the controller driver diverges from what other drivers
> do it's going to lead to interoperability skew for drivers.
> For the warm reset function I'd suggest adding something which checks to
> see if the link is already active and suppresses the warm reset in that
> case.  That will avoid slowing everything down with spurious warm resets
> when the link is already runnning and other drivers assume they need to
> bring it up - with the way things are structured at present many warm
> resets requested by other drivers are likely to be spurious.
ok, i will add the check in warm reset.

> Ideally the core would keep track of this and transparently trigger the
> warm reset when required, but driver local is fine since that's not
> there yet.
>> >> +     ac_glbctrl = S3C_AC97_GLBCTRL_ACLINKON;
>> >> +     writel(ac_glbctrl, s3c_ac97.regs + S3C_AC97_GLBCTRL);
>> >> +     msleep(1);
>> > This also looks a bit odd, ACLINKON sounds like bringing up the link
>> > which is what a warm reset does.
>> As shown in FSM of SoCs manual, this sets the controller state to READY.
>> Please have a look at any manual's AC97 chapter.
> Right, but why is this being done by this function and not, for example,
> by the warm reset?  It's the structure of the code I'm commenting on
> rather than the operations that get performed on the hardware.
I assume the ALSA definition of cold/warm reset is same as that of
the AC97 controller. Anything remaining should be done only when necessary.
For ex, the ALSA might want to leave controller after just cold/warm
reset ... as
the SoC manual says it's in low-power mode without the AC-link on.

>> >> +lb5:
>> >> +     free_irq(irq_res->start, NULL);
>> > Perhaps a better name than 'lb' - err, or fail or something.  lb means
>> > nothing to me at least.
>> means label to me :)
> If you'd spelt out label I'd probably have been OK, but in English lb is
> normally only an abbreviation for pounds as a unit of weight.
ok, will rename the labels.

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