Re: [PATCH 3/3] mailbox: pcc: Fix command timeout due to missed interrupt

[Sudeep Holla <sudeep.holla@arm.com>]

On Thu, Jul 23, 2026 at 11:57:58AM -0400, Adam Young wrote:
> 
> On 7/23/26 05:16, Sudeep Holla wrote:
> > On Wed, Jul 22, 2026 at 11:10:51PM -0400, Adam Young wrote:
> > > +	/*
> > > +	 * Set chan_in_use before ringing the doorbell so a fast completion
> > > +	 * interrupt is not mistaken for a shared interrupt from another
> > > +	 * subspace. Use WRITE_ONCE() for the lockless flag update. The
> > > +	 * ordered MMIO accessor used to ring the doorbell keeps this store
> > > +	 * visible before the platform is notified.
> > > +	 */
> > > +	if (pchan->plat_irq > 0)
> > > +		WRITE_ONCE(pchan->chan_in_use, true);
> > >   	ret = pcc_chan_reg_read_modify_write(&pchan->db);
> > >   	if (!ret && pchan->plat_irq > 0)
> > > -		pchan->chan_in_use = true;
> > > +		WRITE_ONCE(pchan->chan_in_use, false);
> > >   	return ret;
> > >   }
> > > -- 
> > > 2.43.0
> > > iAt the end of the above code,
> > >   WRITE_ONCE(pchan->chan_in_use, false);
> > >   should be
> > >   WRITE_ONCE(pchan->chan_in_use, true);
> > > 
> > > In order to keep the original semantics.  The flag is cleared when the
> > > messages is ACKed, not here.  This version causes a hang.
> > > 
> > Did you run and seeing hang or just code inspection. If latter, have you
> > considered that modified code sets it true before doorbell is rung and
> > set to false only if there is a failure to ring the doorbell ?
> > 
> Yes, I saw the hang, and debugged to see this line semantically different. 
> I changed it to true and things resumed working.  !ret is 0  so that happens
> in the success case.
> 

My mistake, I must pay more attention 🙁. I wanted it to be error case
and always read it as if(ret..) instead of if(!ret..), sorry for that.

-- 
Regards,
Sudeep