RE: [PATCH V2] firmware: arm_scmi: Make scmi core independent of transport type

From: Peng Fan <peng.fan@nxp.com>
To: Arnd Bergmann <arnd@arndb.de>, Viresh Kumar <viresh.kumar@linaro.org>
Cc: Jassi Brar <jassisinghbrar@gmail.com>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"cristian.marussi@arm.com" <cristian.marussi@arm.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH V2] firmware: arm_scmi: Make scmi core independent of transport type
Date: Wed, 15 Jan 2020 08:20:26 +0000	[thread overview]
Message-ID: <AM0PR04MB448109C21B4C6A2C923FF4D988370@AM0PR04MB4481.eurprd04.prod.outlook.com> (raw)
In-Reply-To: <CAK8P3a1cByQrhKV=8gRASNy74p8=WKfi1ZU13S2OpFQRjohUsg@mail.gmail.com>

> Subject: Re: [PATCH V2] firmware: arm_scmi: Make scmi core independent of
> transport type
> 
> On Tue, Jan 14, 2020 at 12:11 PM Viresh Kumar <viresh.kumar@linaro.org>
> wrote:
> >
> > On 14-01-20, 10:56, Arnd Bergmann wrote:
> > > My point was that you cannot mix __iomem accesses with pointer
> > > accesses. As I understood it, the current version uses a pointer to
> > > a
> >
> > The current version is stupid as I misunderstood the whole __iomem
> > thing and just dropped it :)
> >
> > > hardware mailbox with structured data, so you have to use ioremap()
> > > to get a token you can pass into ioread(), but (some of) the new
> > > transport types would just be backed by regular RAM, on which this
> > > is not a well-defined operation and you have to use memremap() and
> > > memcpy() instead.
> >
> > Okay, I think I understand that a bit now. So here are the things
> > which I may need to do now:
> >
> > - Maybe move payload to struct scmi_mailbox structure, as that is the
> >   transport dependent structure..
> >
> > - Do ioremap, etc in mailbox.c only instead of driver.c
> >
> > - Provide more ops in struct scmi_transport_ops to provide read/write
> >   helpers to the payload and implement the ones based on
> >   ioread/iowrite in mailbox.c ..
> >
> > Am I thinking in the right direction now ?
> 
> That sounds about right. What I'm still not sure about is whether the current
> kernel code is actually correct and should use iomeap() in the first place. Can
> you confirm that all current hardware implementations actually use MMIO
> type registers here rather than just rely on a buffer in RAM?

i.MX8(alought not use SCMI) use MU(message unit) to transfer data between
Acore and Mcore firmware, not using shared memory.

Thanks,
Peng.

> 
>       Arnd
> 
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