linux-kernel - Re: [PATCH] firmware: arm_scmi: fix voltage description in failure cases

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Message-ID: <ZrIoKiQVLKuA-YWh@bogus>
Date: Tue, 6 Aug 2024 14:42:02 +0100
From: Sudeep Holla <sudeep.holla@....com>
To: Cristian Marussi <cristian.marussi@....com>
Cc: Etienne Carriere <etienne.carriere@...s.st.com>,
	linux-kernel@...r.kernel.org, arm-scmi@...r.kernel.org,
	Sudeep Holla <sudeep.holla@....com>,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] firmware: arm_scmi: fix voltage description in failure
 cases

On Thu, Aug 01, 2024 at 11:58:19AM +0100, Cristian Marussi wrote:
> On Fri, Jul 26, 2024 at 04:16:03PM +0100, Sudeep Holla wrote:
> > On Thu, Jul 25, 2024 at 08:53:17AM +0200, Etienne Carriere wrote:
> > > Reset the reception buffer max size when a voltage domain description
> > > request fails, for example when the voltage domain returns an access
> > > permission error (SCMI_ERR_ACCESS) unless what only a single 32bit
> > > word is read back for the remaining voltage description requests
> > > responses leading to invalid information. The side effect of this
> > > issue is that the voltage regulators registered from those remaining
> > > SCMI voltage domain were assigned a wrong regulator name.
> > > 
> > > Signed-off-by: Etienne Carriere <etienne.carriere@...s.st.com>
> > > ---
> > >  drivers/firmware/arm_scmi/voltage.c | 4 +++-
> > >  1 file changed, 3 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/firmware/arm_scmi/voltage.c b/drivers/firmware/arm_scmi/voltage.c
> > > index 2175ffd6cef5..f1a7c04ae820 100644
> > > --- a/drivers/firmware/arm_scmi/voltage.c
> > > +++ b/drivers/firmware/arm_scmi/voltage.c
> > > @@ -229,8 +229,10 @@ static int scmi_voltage_descriptors_get(const struct scmi_protocol_handle *ph,
> > >  		/* Retrieve domain attributes at first ... */
> > >  		put_unaligned_le32(dom, td->tx.buf);
> > >  		/* Skip domain on comms error */
> > > -		if (ph->xops->do_xfer(ph, td))
> > > +		if (ph->xops->do_xfer(ph, td)) {
> > > +			ph->xops->reset_rx_to_maxsz(ph, td);
> > 
> > I am fine with this to keep it simple, but thought I will check my thoughts.
> > We usually use reset_rx_to_maxsz in iterators as we don't know the expected
> > size of the response, whereas here it must be max sizeof(*resp_dom).
> > 
> > That said, we don't have any helpers and changing xfer->rx.len directly
> > doesn't looks good ? Or may be it is OK ? Thoughts ?
> 
> We do not access those xfer internal field explicitly from the protocol layer
> (beside once in Base)...and surely not on write....in the past I was even
> tempted to try to make these internal stuff untouchable by the protocol layer...
> ...that's the reason of course for the existence of reset_rx_to_maxsz() helpers
> ....not sure if it is worth adding another helper for this, given that the
> using the maxsz should have any adverse effect (unless I am missing
> something of course :P).
> 
> This kind of 'issues' are really common whenever in the SCMI stack we
> reuse the same allocated xfer across multiple do_xfers in a loop
> (reusing seq_nums is another thing...) since we wanted to avoid the
> penalty of resetting some of these automatically on each do_xfer()...
> 
> ....we could think of some mechanism to transparently reset/fill such xfer
> fields automatically if the core detects a 'reuse'....got to check first,
> though, if this does not break some of the current usage patterns...and
> I would not say it is a high prio thing to explore as of now...
> 

Fair enough, I will merge this as is. I think it should be fine. My suggestion
might simply complicates things unnecessarily. Lets not do it unless this
becomes repeating pattern.

-- 
Regards,
Sudeep