Messages in this thread | | | Date | Wed, 25 Aug 2021 19:49:15 +0100 | From | Cristian Marussi <> | Subject | Re: [PATCH v4 11/12] [RFC] firmware: arm_scmi: Add sync_cmds_atomic_replies transport flag |
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On Wed, Aug 25, 2021 at 01:17:47PM -0400, Jim Quinlan wrote: > On Wed, Aug 25, 2021 at 12:38 PM Florian Fainelli <f.fainelli@gmail.com> wrote: > > > > > >
Hi Florian and Jim,
> > On 8/24/2021 3:59 PM, Cristian Marussi wrote: > > > A flag is added to let the transport signal the core that its handling of > > > synchronous command messages implies that, after .send_message has returned > > > successfully, the requested command can be assumed to be fully and > > > completely executed on SCMI platform side so that any possible response > > > value is already immediately available to be retrieved by a .fetch_reponse: > > > in other words the polling phase can be skipped in such a case and the > > > response values accessed straight away. > > > > > > Note that all of the above applies only when polling mode of operation was > > > selected by the core: if instead a completion IRQ was found to be available > > > the normal response processing path based on completions will still be > > > followed. > > > > This might actually have to be settable on a per-message basis ideally > > since we may be transporting short lived SCMI messages for which the > > completion can be done at SMC time, and long lived SCMI messages (e.g.: > > involving a voltage change) for which we would prefer a completion > > interrupt. Jim, what do you think? > Even if the SCMI main driver could be configured this way in an > elegant manner, I'm not sure that there is a clean way of specifying > this attribute on a per-message basis. Certainly we could do this > with our own protocols, but many of our "long lived" messages are the > Perf protocol's set_level command. At any rate, let me give it some > thought. >
The new flag .sync_cmds_atomic_replies applies only when polling mode has been selected for a specific cmd transaction, which means when no completion IRQ was found available OR if xfer.poll_completion was excplicitly set for a specific command.
At the moment in this series (unknown bugs apart :D), if you have a channel configured with a completion IRQ and the .sync_cmds_atomic_replies set for the transport, this latter flag would be generally ignored and a wait_for_completion() will be normally used upon reception of the completionIRQ, UNLESS you specify that one specific command has to be polled using the per message xfer.poll_completion flag: so you should be already able to selectively use a polling which immediately returns after the smc by setting xfer.poll_completion for that specific short lived message (since sync_cmds_atomic_replies is set and applies to pollmode). On the other side any other LONG lived message will be naturally handled via completionIRQ + wait_for_completion. (at least that was the aim..)
!!! NOTE that you'll have also to drop
[PATCH v4 10/12] [RFC] firmware: arm_scmi: Make smc transport atomic
from this series for the wait_completion to happen as you wish.
As said I'm not sure that this whole mixing of polling and IRQs on the same channel on a regular won't cause any issues: any feedback on this from your setup is much appreciated. (maybe it's fine for SMC transport, but it led to a bit of hell in the past with mboxes AFAIK...)
Thanks a lot again for your feedback, I'll have to chat with Sudeep about the various issues/configs possibility that we discussed and I'll keep you in the loop.
Thanks, Cristian
P.S.: I'll be off for a few weeks, so even though I'll keep an eye on the mail, I cannot guarantee any responsiveness :D
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