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

From: Sudeep Holla <[email-masked]>
Date: Tue, 19 May 2026 17:25:29 +0100

On Tue, May 19, 2026 at 09:54:47PM +0800, lihuisong (C) wrote:
> 
> On 5/19/2026 3:30 AM, 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)")
> Not fix above commit.
> mbox_chan_txdone() was added in below patch.
> Fixes: 9c753f7c953c (mailbox: pcc: Mark Tx as complete in PCC IRQ handler)
> > Signed-off-by: Adam Young <[email-masked]>
> > 
> > ---
> > ---
> >   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 it is not necessary. This function just return -EIO on failure.
> 
> >   	/*
> >   	 * 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);
> > +	mbox_chan_txdone(chan, rc);
> @Sudeep, I have always had doubts about the addition of this line of code in
> the
>  commit 9c753f7c953c (mailbox: pcc: Mark Tx as complete in PCC IRQ handler).
> The patch seems to avoid the timeouts in the mailbox core according to its
> commit log.
> Regardless of whether the command succeeds or fails, each mbox client
> driver, like cppc_acpi/acpi_pcc，kunpeng_hccs and so on, is responsible to
> call mbox_chan_txdone() to tell mailbox core.

Few controller drivers do have mbox_chan_txdone(), so Tx complete is detected
by PCC, so not sure why you think this is not the right place to do. The irq
is to indicate the completion. I am confused as why you think otherwise.
It is defined in include/linux/mailbox_controller.h for the same reason.

The client drivers can you mbox_client_txdone() if they wish to as defined
in include/linux/mailbox_client.h

> This is done after executing mbox_chan_received_data(). So I think this line
> in this function is redundant.

No, I think otherwise, see details above.

-- 
Regards,
Sudeep