在 2025/3/3 18:51, Sudeep Holla 写道:
The PCC mailbox interrupt handler (pcc_mbox_irq()) currently checks
for command completion flags and any error status before clearing the
interrupt.
The below sequence highlights an issue in the handling of PCC mailbox
interrupts, specifically when dealing with doorbell notifications and
acknowledgment between the OSPM and the platform where type3 and type4
channels are sharing the interrupt.
Platform Firmware OSPM/Linux PCC driver
------------------------------------------------------------------------
build message in shmem
ring type3 channel doorbell
receives the doorbell interrupt
process the message from OSPM
build response for the message
ring the platform ack interrupt to OSPM
--->
build notification in type4 channel
start processing in pcc_mbox_irq()
enter pcc handler for type4 chan
command complete cleared
read the notification
<--- clear platform ack irq
* no effect from above as platform ack irq *
* not yet triggered on this channel *
ring the platform ack irq on type4 channel
--->
leave pcc handler for type4 chan
enter pcc handler for type3 chan
command complete set
read the response
<--- clear platform ack irq
leave pcc handler for type3 chan
leave pcc_mbox_irq() handler
start processing in pcc_mbox_irq()
enter pcc handler for type4 chan
leave pcc handler for type4 chan
enter pcc handler for type3 chan
leave pcc handler for type3 chan
leave pcc_mbox_irq() handler
This is not easy to understand to me.
The issue as below described is already very clear to me.
So suggest remove above flow graph.
The key issue occurs when OSPM tries to acknowledge platform ack
interrupt for a notification which is ready to be read and processed
but the interrupt itself is not yet triggered by the platform.
This ineffective acknowledgment leads to an issue later in time where
the interrupt remains pending as we exit the interrupt handler without
clearing the platform ack interrupt as there is no pending response or
notification. The interrupt acknowledgment order is incorrect.
Has this issue been confired? It's more better if has the log.😁
But it seems a valid issue.
To resolve this issue, the platform acknowledgment interrupt should
always be cleared before processing the interrupt for any notifications
or response.
AFAIC，always clearing the platform ack interrupt first which is also the
communication flow as ACPI spec described.
I am not sure if it is ok when triggering interrupt and clearing
interrupt occur concurrently.
But this scenario is always possible. I think It doesn't matter with
this patch. It's just my confusion.
Reported-by: Robbie King <robbiek@xxxxxxxxxxxxxx>
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
Lgtm,
Reviewed-by: Huisong Li <lihuisong@xxxxxxxxxx>
---
drivers/mailbox/pcc.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/mailbox/pcc.c b/drivers/mailbox/pcc.c
index f2e4087281c70eeb5b9b33371596613a371dff4f..4c582fa2b8bf4c9a9368dba8220f567555dba963 100644
--- a/drivers/mailbox/pcc.c
+++ b/drivers/mailbox/pcc.c
@@ -313,6 +313,10 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
int ret;
pchan = chan->con_priv;
+
+ if (pcc_chan_reg_read_modify_write(&pchan->plat_irq_ack))
+ return IRQ_NONE;
+
if (pchan->type == ACPI_PCCT_TYPE_EXT_PCC_MASTER_SUBSPACE &&
!pchan->chan_in_use)
return IRQ_NONE;
@@ -330,9 +334,6 @@ static irqreturn_t pcc_mbox_irq(int irq, void *p)
return IRQ_NONE;
}
- if (pcc_chan_reg_read_modify_write(&pchan->plat_irq_ack))
- return IRQ_NONE;
-
/*
* Clear this flag immediately after updating interrupt ack register
* to avoid possible race in updatation of the flag from
