Re: [EXTERNAL] Re: [PATCH v1 RESEND] SoundWire: Allow Prepare command for Simplified_CP_SM

[Richard Fitzgerald]

On 12/02/2026 4:17 pm, Holalu Yogendra, Niranjan wrote:
> Apologies for the late response.
> > On 2/10/26 22:34 Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxx> wrote:
> > Subject: Re: [PATCH v1 RESEND] SoundWire: Allow Prepare command for Simplified_CP_SM
> >
> > On 2/10/26 12: 08, Holalu Yogendra, Niranjan wrote: >> On 2/9/26 20: 13,
> > Pierre-Louis Bossart <pierre-louis. bossart@ linux. dev> wrote:
> > On 2/10/26 12:08, Holalu Yogendra, Niranjan wrote:
> > > > On 2/9/26 20:13, Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxx> wrote:
> > > > On 2/9/26 08: 09, Niranjan H Y wrote:
>
> > Are you referring to the DPN_IntStat::PortReady bit? IOW do the errors during
> > prepare happen because the interrupt is not generated?
> > If that is the case, then you should be aware of the thread "soundwire:
> > stream: Prepare ports in parallel to reduce stream start latency", where it was
> > agreed that the use of the PortReady interrupt is broken. We do need to move
> > to a different code where we have a polling loop on the
> > DPN_PrepareStatus::NotFinished bits.
>
> Thanks for the info.
>
> > So is the problem in the interrupt generation, or is the problem with the 'Not
> > Finished' bits?
> Both, while using Full CP_SM on a simplified CP_SM device:
> * First problem: the interrupt will not get generated on a simple CP_SM device.
> * Second problem: even after timeout waiting for interrupt with huge delays,
>    we can't rely on 'Not Finished' bits, causing timeout errors.
>    In the current code for full CP_SM, 'Not Finished' = 0 is a good response even
>    with timeout.
That's because it _IS_ a good response. If the part is reporting
NotFinished=0, then it's good to go and we don't need to treat it as a
timeout. The timeout is caused by the deadlock that Pierre mentioned.
Full CP_SM will always timeout because that code is holding the bus
lock, which blocks the interrupt handler.

Ignoring the timeout if NotFinished=0 was a workaround until I found
time to fix the interrupt handling. Otherwise full CP_SM would never
work.

We've now decided to replace that code with a polling loop instead of
using interrupts.

> > If that works then an alternate solution to this patch would be to quirk all TI
> > devices to use the regular state machine, and use the polling loop as
> > suggested by Richard Fitzgerald.
> > I think it's worth exploring what happens if the PortReady interrupt is not
> > used. If that's broken as well, then your solution would work but needs
> > more/better comments indeed.
> Currently, we have one device which needs this workaround.
> Initially, it looked like a generic solution to me. However, if it makes sense,
> I can implement sdw_slave_ops->port_prep to make custom changes
> for the required devices only, handle any errors and drop this patch.
> Please suggest.
>
> Regards
> Niranjan