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Date: Thu, 23 Sep 2021 16:03:19 +0100 From: Cristian Marussi <cristian.marussi@....com> To: Jim Quinlan <james.quinlan@...adcom.com> Cc: Florian Fainelli <f.fainelli@...il.com>, open list <linux-kernel@...r.kernel.org>, "moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>, Sudeep Holla <sudeep.holla@....com>, Jonathan Cameron <Jonathan.Cameron@...wei.com>, etienne.carriere@...aro.org, Vincent Guittot <vincent.guittot@...aro.org>, Souvik Chakravarty <souvik.chakravarty@....com> Subject: Re: [PATCH v4 11/12] [RFC] firmware: arm_scmi: Add sync_cmds_atomic_replies transport flag On Thu, Aug 26, 2021 at 02:29:21PM -0400, Jim Quinlan wrote: > On Wed, Aug 25, 2021 at 2:49 PM Cristian Marussi > <cristian.marussi@....com> wrote: > > > > 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@...il.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. > > Hi Cristian, > Hi Jim, > I've tested all commits on our SMC-based system. I also tested all commits > minus "10/12 [RFC] firmware: arm_scmi: Make smc transport atomic". > This was a basic stress test, not a comprehensive one. So > > Tested-by: Jim Quinlan <james.quinlan@...adcom.com> > > Of course I have a strong preference for omitting "10/12 [RFC]" :-). > FWIW, if you are not planning on dropping this commit, perhaps there > could be a transport > node in the DT, and that could contain the a bool property > "smc-atomic-capable"? > I just posted V5 on this SCMI atomic transport series, where the atomic mode behaviour of a transport can be selected by a Kconfig which is defined as default N: so this new series should behave out-of-the-box like with the previous one when you had dropped as a whole the SMC atomic patch. Any feedback welcome. Thanks, Cristian
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