Hello Sudeep, On Fri, 26 Jul 2019 at 15:46, Sudeep Holla <sudeep.ho...@arm.com> wrote: > > Sometimes platfom may take too long to respond to the command and OS > might timeout before platform transfer the ownership of the shared > memory region to the OS with the response. > > Since the mailbox channel associated with the channel is freed and new > commands are dispatch on the same channel, OS needs to wait until it > gets back the ownership. If not, either OS may end up overwriting the > platform response for the last command(which is fine as OS timed out > that command) or platform might overwrite the payload for the next > command with the response for the old. > > The latter is problematic as platform may end up interpretting the > response as the payload. In order to avoid such race, let's wait until > the OS gets back the ownership before we prepare the shared memory with > the payload for the next command. > > Reported-by: Jim Quinlan <james.quin...@broadcom.com> > Signed-off-by: Sudeep Holla <sudeep.ho...@arm.com> > --- > drivers/firmware/arm_scmi/driver.c | 8 ++++++++ > 1 file changed, 8 insertions(+) > > diff --git a/drivers/firmware/arm_scmi/driver.c > b/drivers/firmware/arm_scmi/driver.c > index 69bf85fea967..765573756987 100644 > --- a/drivers/firmware/arm_scmi/driver.c > +++ b/drivers/firmware/arm_scmi/driver.c > @@ -265,6 +265,14 @@ static void scmi_tx_prepare(struct mbox_client *cl, void > *m) > struct scmi_chan_info *cinfo = client_to_scmi_chan_info(cl); > struct scmi_shared_mem __iomem *mem = cinfo->payload; > > + /* > + * Ideally channel must be free by now unless OS timeout last > + * request and platform continued to process the same, wait > + * until it releases the shared memory, otherwise we may endup > + * overwriting it's response with new command payload or vice-versa
minor typo: s/it's/its/ maybe also s/command/message/ regards, etienne > + */ > + spin_until_cond(ioread32(&mem->channel_status) & > + SCMI_SHMEM_CHAN_STAT_CHANNEL_FREE); > /* Mark channel busy + clear error */ > iowrite32(0x0, &mem->channel_status); > iowrite32(t->hdr.poll_completion ? 0 : SCMI_SHMEM_FLAG_INTR_ENABLED, > -- > 2.17.1 >