Re: [PATCH] firmware: arm_scmi: Relax CLOCK_DESCRIBE_RATES out-of-spec checks

From: Cristian Marussi
Date: Fri Jun 17 2022 - 07:12:58 EST


On Thu, Jun 16, 2022 at 07:02:49PM +0100, Robin Murphy wrote:
> On 2022-06-16 18:03, Cristian Marussi wrote:
> > A reply to CLOCK_DESCRIBE_RATES issued against a non rate-discrete clock
> > should be composed of a triplet of rates descriptors (min/max/step)
> > returned all in one reply message.
> >
> > This is not always the case when dealing with some SCMI server deployed in
> > the wild: relax such constraint while maintaining memory safety by checking
> > carefully the returned payload size.
> >
> > While at that cleanup a stale debug printout.
>
> I know we're testing on the same platform so it's of limited value, but for
> the record this does indeed make my display work again, so FWIW:
>
> Tested-by: Robin Murphy <robin.murphy@xxxxxxx>
>
> Thanks for the quick turnaround!
> Robin.
>

Thanks Robin.

Testing is never enough :P

Thanks,
Cristian

> > Fixes: 7bc7caafe6b1 ("firmware: arm_scmi: Use common iterators in the clock protocol")
> > Signed-off-by: Cristian Marussi <cristian.marussi@xxxxxxx>
> > ---
> > drivers/firmware/arm_scmi/clock.c | 26 +++++++++++++++++++++++++-
> > drivers/firmware/arm_scmi/driver.c | 1 +
> > drivers/firmware/arm_scmi/protocols.h | 3 +++
> > 3 files changed, 29 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/firmware/arm_scmi/clock.c b/drivers/firmware/arm_scmi/clock.c
> > index c7a83f6e38e5..3ed7ae0d6781 100644
> > --- a/drivers/firmware/arm_scmi/clock.c
> > +++ b/drivers/firmware/arm_scmi/clock.c
> > @@ -194,6 +194,7 @@ static int rate_cmp_func(const void *_r1, const void *_r2)
> > }
> > struct scmi_clk_ipriv {
> > + struct device *dev;
> > u32 clk_id;
> > struct scmi_clock_info *clk;
> > };
> > @@ -223,6 +224,29 @@ iter_clk_describe_update_state(struct scmi_iterator_state *st,
> > st->num_returned = NUM_RETURNED(flags);
> > p->clk->rate_discrete = RATE_DISCRETE(flags);
> > + /* Warn about out of spec replies ... */
> > + if (!p->clk->rate_discrete &&
> > + (st->num_returned != 3 || st->num_remaining != 0)) {
> > + dev_warn(p->dev,
> > + "Out-of-spec CLOCK_DESCRIBE_RATES reply for %s - returned:%d remaining:%d rx_len:%zd\n",
> > + p->clk->name, st->num_returned, st->num_remaining,
> > + st->rx_len);
> > +
> > + /*
> > + * A known quirk: a triplet is returned but num_returned != 3
> > + * Check for a safe payload size and fix.
> > + */
> > + if (st->num_returned != 3 && st->num_remaining == 0 &&
> > + st->rx_len == sizeof(*r) + sizeof(__le32) * 2 * 3) {
> > + st->num_returned = 3;
> > + st->num_remaining = 0;
> > + } else {
> > + dev_err(p->dev,
> > + "Cannot fix out-of-spec reply !\n");
> > + return -EPROTO;
> > + }
> > + }
> > +
> > return 0;
> > }
> > @@ -255,7 +279,6 @@ iter_clk_describe_process_response(const struct scmi_protocol_handle *ph,
> > *rate = RATE_TO_U64(r->rate[st->loop_idx]);
> > p->clk->list.num_rates++;
> > - //XXX dev_dbg(ph->dev, "Rate %llu Hz\n", *rate);
> > }
> > return ret;
> > @@ -275,6 +298,7 @@ scmi_clock_describe_rates_get(const struct scmi_protocol_handle *ph, u32 clk_id,
> > struct scmi_clk_ipriv cpriv = {
> > .clk_id = clk_id,
> > .clk = clk,
> > + .dev = ph->dev,
> > };
> > iter = ph->hops->iter_response_init(ph, &ops, SCMI_MAX_NUM_RATES,
> > diff --git a/drivers/firmware/arm_scmi/driver.c b/drivers/firmware/arm_scmi/driver.c
> > index c1922bd650ae..8b7ac6663d57 100644
> > --- a/drivers/firmware/arm_scmi/driver.c
> > +++ b/drivers/firmware/arm_scmi/driver.c
> > @@ -1223,6 +1223,7 @@ static int scmi_iterator_run(void *iter)
> > if (ret)
> > break;
> > + st->rx_len = i->t->rx.len;
> > ret = iops->update_state(st, i->resp, i->priv);
> > if (ret)
> > break;
> > diff --git a/drivers/firmware/arm_scmi/protocols.h b/drivers/firmware/arm_scmi/protocols.h
> > index c679f3fb8718..51c31379f9b3 100644
> > --- a/drivers/firmware/arm_scmi/protocols.h
> > +++ b/drivers/firmware/arm_scmi/protocols.h
> > @@ -179,6 +179,8 @@ struct scmi_protocol_handle {
> > * @max_resources: Maximum acceptable number of items, configured by the caller
> > * depending on the underlying resources that it is querying.
> > * @loop_idx: The iterator loop index in the current multi-part reply.
> > + * @rx_len: Size in bytes of the currenly processed message; it can be used by
> > + * the user of the iterator to verify a reply size.
> > * @priv: Optional pointer to some additional state-related private data setup
> > * by the caller during the iterations.
> > */
> > @@ -188,6 +190,7 @@ struct scmi_iterator_state {
> > unsigned int num_remaining;
> > unsigned int max_resources;
> > unsigned int loop_idx;
> > + size_t rx_len;
> > void *priv;
> > };