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From:   Peng Fan <peng.fan@nxp.com>
To:     Sudeep Holla <sudeep.holla@arm.com>
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Subject: RE: [PATCH V4 2/2] firmware: arm_scmi: add smc/hvc transport
Thread-Topic: [PATCH V4 2/2] firmware: arm_scmi: add smc/hvc transport
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Date:   Wed, 4 Mar 2020 12:49:32 +0000
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Hi Sudeep,

> Subject: Re: [PATCH V4 2/2] firmware: arm_scmi: add smc/hvc transport
>=20
> On Tue, Mar 03, 2020 at 10:06:59AM +0800, peng.fan@nxp.com wrote:
> > From: Peng Fan <peng.fan@nxp.com>
> >
> > Take arm,smc-id as the 1st arg, leave the other args as zero for now.
> > There is no Rx, only Tx because of smc/hvc not support Rx.
> >
> > Signed-off-by: Peng Fan <peng.fan@nxp.com>
>=20
> [...]
>=20
> > +static int smc_send_message(struct scmi_chan_info *cinfo,
> > +			    struct scmi_xfer *xfer)
> > +{
> > +	struct scmi_smc *scmi_info =3D cinfo->transport_info;
> > +	struct arm_smccc_res res;
> > +
> > +	shmem_tx_prepare(scmi_info->shmem, xfer);
>=20
> How do we protect another thread/process on another CPU going and
> modifying the same shmem with another request ? We may need notion of
> channel with associated shmem and it is protected with some lock.

This is valid concern. But I think if shmem is shared bwteen protocols,
the access to shmem should be protected in=20
drivers/firmware/arm_scmi/driver.c: scmi_do_xfer,
because send_message and fetch_response both touches shmem

The mailbox transport also has the issue you mentioned, I think.

Thanks,
Peng.
>=20
> --
> Regards,
> Sudeep