linux-kernel - RE: [PATCH V4 2/2] firmware: arm

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Date:   Wed, 4 Mar 2020 12:49:32 +0000
From:   Peng Fan <peng.fan@....com>
To:     Sudeep Holla <sudeep.holla@....com>
CC:     "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "viresh.kumar@...aro.org" <viresh.kumar@...aro.org>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        dl-linux-imx <linux-imx@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: RE: [PATCH V4 2/2] firmware: arm_scmi: add smc/hvc transport

Hi Sudeep,

> Subject: Re: [PATCH V4 2/2] firmware: arm_scmi: add smc/hvc transport
> 
> On Tue, Mar 03, 2020 at 10:06:59AM +0800, peng.fan@....com wrote:
> > From: Peng Fan <peng.fan@....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@....com>
> 
> [...]
> 
> > +static int smc_send_message(struct scmi_chan_info *cinfo,
> > +			    struct scmi_xfer *xfer)
> > +{
> > +	struct scmi_smc *scmi_info = cinfo->transport_info;
> > +	struct arm_smccc_res res;
> > +
> > +	shmem_tx_prepare(scmi_info->shmem, xfer);
> 
> 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 
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.
> 
> --
> Regards,
> Sudeep