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

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.