Re: [PATCH v02] mailbox: pcc: report errors for PCC clients

[Adam Young <admiyo@amperemail.onmicrosoft.com>]

I am geting ready to resubmit this patch along with a series of other 
PCC based changes that show how it is necessary

for MCTP-PCC.

On 5/19/26 09:23, Sudeep Holla wrote:
> On Mon, May 18, 2026 at 03:30:06PM -0400, Adam Young wrote:
>> The tx_done callback function has a return code (rc) parameter
>> that the tx_done callback can use to determine how to handle an error.
>> However the IRQ handler was not setting that value if there is an error.
>>
>> The following clients are affected:
>>
>> drivers/acpi/cppc_acpi.c
>> drivers/i2c/busses/i2c-xgene-slimpro.c
>> drivers/hwmon/xgene-hwmon.c
>> drivers/soc/hisilicon/kunpeng_hccs.c
>> drivers/devfreq/hisi_uncore_freq.c
>>
>> All of these only use the error code to report, so they
>> are expecting an error code to come thorugh, but they
>> do not modify behavior based on this code.
>>
>> In the case of an error code in the IRQ, the handler was returning
>> IRQ_NONE which is not correct:  the IRQ handler was matched
>> to the IRQ.  This mean that multiple error codes returned from
>> a PCC triggered interrupt would end up disabling the device.
>>
>> In addition, if the error code IRQ was coming from a Type4 Device that was
>> expecting an IRQ response, that device would then be hung.
>>
>> Fixes: c45ded7e1135 ("mailbox: pcc: Add support for PCCT extended PCC subspaces(type 3/4)")
>> Signed-off-by: Adam Young <admiyo@os.amperecomputing.com>
>>
>> ---
>> ---
>>   drivers/mailbox/pcc.c | 9 +++++----
>>   1 file changed, 5 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
>> index 636879ae1db7..16b9ce087b9e 100644
>> --- a/drivers/mailbox/pcc.c
>> +++ b/drivers/mailbox/pcc.c
>> @@ -314,6 +314,7 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
>>   {
>>   	struct pcc_chan_info *pchan;
>>   	struct mbox_chan *chan = p;
>> +	int rc;
>>   
>>   	pchan = chan->con_priv;
>>   
>> @@ -327,8 +328,7 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
>>   	if (!pcc_mbox_cmd_complete_check(pchan))
>>   		return IRQ_NONE;
>>   
>> -	if (pcc_mbox_error_check_and_clear(pchan))
>> -		return IRQ_NONE;
>> +	rc = pcc_mbox_error_check_and_clear(pchan);
> I think we may have to skip the check inside pcc_mbox_error_check_and_clear()
> for Type 4 channel as the spec expects OSPM to ignore it. It is a separate
> fix, just noting that here.

I will submit this as a pre-req patch.


>
>>   
>>   	/*
>>   	 * Clear this flag after updating interrupt ack register and just
>> @@ -337,8 +337,9 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
>>   	 * required to avoid any possible race in updatation of this flag.
>>   	 */
>>   	pchan->chan_in_use = false;
>> -	mbox_chan_received_data(chan, NULL);
>> -	mbox_chan_txdone(chan, 0);
>> +	if (!rc)
>> +		mbox_chan_received_data(chan, NULL);
> Not sure if making this conditional is good as some platforms may expect
> it to move the state machine, I am not sure 100% just thinking aloud here.

That is currently not the case.  Right now, and error code 
short-circuits and further execution of the IRC handler.  I think that 
those drivers would need to be changes to have a tx_done callback instead.


>