Re: [PATCH 1/4] firmware: arm_scmi: Make mutex channel specific

[Sudeep Holla <sudeep.holla@arm.com>]

On Wed, Apr 01, 2020 at 01:12:37AM +0000, Peng Fan wrote:
> Hi Sudeep,
>
> > Subject: [PATCH 1/4] firmware: arm_scmi: Make mutex channel specific
> >
> > In order to support multiple SMC/HVC transport channels with associated
> > shared memory,
>
> Does this mean each channel will have its own shared memory? Or
> All channels share the same shared memory?
>

It depends on platform firmware and DT. If there is only one shmem at
the top level scmi node, all share that single channel. If some/all
protocols have their own channel, they there must be shmem entry in the
corresponding child node.

> it is better to maintain the mutex per channel instead of
> > existing global one.
>
> If all channels shared the same memory, use per channel mutex lock
> will not be able to prevent other channels accessing shared memory
> at the same time.
>

No we don't create channel per protocol. If they share, we just share
the channel pointer. Look at:

       if (!info->desc->ops->chan_available(dev, idx)) {
                cinfo = idr_find(idr, SCMI_PROTOCOL_BASE);
                if (unlikely(!cinfo)) /* Possible only if platform has no Rx */
                        return -EINVAL;
                goto idr_alloc;
        }

If a protocol doesn't have a dedicated channel, we just assign the base
protocol channel to it. We don't call chan_setup at all on that channel.
Your patch assumed so but the core driver never did that.

Hope this clarifies you doubt.

--
Regards,
Sudeep