6.6-stable review patch. If anyone has any objections, please let me know.
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From: Cristian Marussi cristian.marussi@arm.com
commit 437a310b22244d4e0b78665c3042e5d1c0f45306 upstream.
On reception of a completion interrupt the shared memory area is accessed to retrieve the message header at first and then, if the message sequence number identifies a transaction which is still pending, the related payload is fetched too.
When an SCMI command times out the channel ownership remains with the platform until eventually a late reply is received and, as a consequence, any further transmission attempt remains pending, waiting for the channel to be relinquished by the platform.
Once that late reply is received the channel ownership is given back to the agent and any pending request is then allowed to proceed and overwrite the SMT area of the just delivered late reply; then the wait for the reply to the new request starts.
It has been observed that the spurious IRQ related to the late reply can be wrongly associated with the freshly enqueued request: when that happens the SCMI stack in-flight lookup procedure is fooled by the fact that the message header now present in the SMT area is related to the new pending transaction, even though the real reply has still to arrive.
This race-condition on the A2P channel can be detected by looking at the channel status bits: a genuine reply from the platform will have set the channel free bit before triggering the completion IRQ.
Add a consistency check to validate such condition in the A2P ISR.
Reported-by: Xinglong Yang xinglong.yang@cixtech.com Closes: https://lore.kernel.org/all/PUZPR06MB54981E6FA00D82BFDBB864FBF08DA@PUZPR06MB... Fixes: 5c8a47a5a91d ("firmware: arm_scmi: Make scmi core independent of the transport type") Cc: stable@vger.kernel.org # 5.15+ Signed-off-by: Cristian Marussi cristian.marussi@arm.com Tested-by: Xinglong Yang xinglong.yang@cixtech.com Link: https://lore.kernel.org/r/20231220172112.763539-1-cristian.marussi@arm.com Signed-off-by: Sudeep Holla sudeep.holla@arm.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/firmware/arm_scmi/common.h | 1 + drivers/firmware/arm_scmi/mailbox.c | 14 ++++++++++++++ drivers/firmware/arm_scmi/shmem.c | 6 ++++++ 3 files changed, 21 insertions(+)
--- a/drivers/firmware/arm_scmi/common.h +++ b/drivers/firmware/arm_scmi/common.h @@ -314,6 +314,7 @@ void shmem_fetch_notification(struct scm void shmem_clear_channel(struct scmi_shared_mem __iomem *shmem); bool shmem_poll_done(struct scmi_shared_mem __iomem *shmem, struct scmi_xfer *xfer); +bool shmem_channel_free(struct scmi_shared_mem __iomem *shmem);
/* declarations for message passing transports */ struct scmi_msg_payld; --- a/drivers/firmware/arm_scmi/mailbox.c +++ b/drivers/firmware/arm_scmi/mailbox.c @@ -45,6 +45,20 @@ static void rx_callback(struct mbox_clie { struct scmi_mailbox *smbox = client_to_scmi_mailbox(cl);
+ /* + * An A2P IRQ is NOT valid when received while the platform still has + * the ownership of the channel, because the platform at first releases + * the SMT channel and then sends the completion interrupt. + * + * This addresses a possible race condition in which a spurious IRQ from + * a previous timed-out reply which arrived late could be wrongly + * associated with the next pending transaction. + */ + if (cl->knows_txdone && !shmem_channel_free(smbox->shmem)) { + dev_warn(smbox->cinfo->dev, "Ignoring spurious A2P IRQ !\n"); + return; + } + scmi_rx_callback(smbox->cinfo, shmem_read_header(smbox->shmem), NULL); }
--- a/drivers/firmware/arm_scmi/shmem.c +++ b/drivers/firmware/arm_scmi/shmem.c @@ -122,3 +122,9 @@ bool shmem_poll_done(struct scmi_shared_ (SCMI_SHMEM_CHAN_STAT_CHANNEL_ERROR | SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE); } + +bool shmem_channel_free(struct scmi_shared_mem __iomem *shmem) +{ + return (ioread32(&shmem->channel_status) & + SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE); +}