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

From: lihuisong (C)

Date: Wed May 20 2026 - 08:11:02 EST


On 5/20/2026 12:25 AM, Sudeep Holla wrote:
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 <admiyo@xxxxxxxxxxxxxxxxxxxxxx>

---
---
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
Which controller driver?
by PCC, so not sure why you think this is not the right place to do. The irq
Because many mbox client drivers call mbox_chan_txdone() after running rx_callback() in mbox_chan_received_data().
These drivers doesn't set chan->cl->tx_block to true.
It seems that the client driver having tx_block need to set chan->tx_complete in tx_tick().
Do you add this code for them?
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
mbox_client_txdone() is used in the case that txdone_method is MBOX_TXDONE_BY_ACK.
And mbox clinte driver using IRQ method need to use mbox_chan_txdone().
It seems that all the current client drivers are used in this way.
These interface internal would verify chan->txdone_method.

In addition, I find that you also modify the txdone_irq/poll in the commit 3349f800609e (mailbox: pcc: Set txdone_irq/txdone_poll based on PCCT flags).
The txdone_method will change from MBOX_TXDONE_BY_ACK to MBOX_TXDONE_BY_POLL on the platform using poll mode.
This may lead to the original mbox client driver printing exceptions in mbox_client_txdone.
I haven't observed it based on the latest code yet, it's just code analysis.

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.