linux-kernel - Re: [PATCH V2] firmware: arm_scmi: Make scmi core independent of transport type

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Date:   Tue, 14 Jan 2020 14:56:15 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Jassi Brar <jassisinghbrar@...il.com>,
        cristian.marussi@....com, peng.fan@....com,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH V2] firmware: arm_scmi: Make scmi core independent of
 transport type

On 13-01-20, 12:36, Arnd Bergmann wrote:
> On Mon, Jan 13, 2020 at 7:42 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > On 10-01-20, 12:15, Arnd Bergmann wrote:
> > > On Fri, Jan 10, 2020 at 10:43 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> > >
> > > Simply dropping the __iomem isn't much better, now you get other
> > > type mismatches.
> >
> > Right. So what exactly do you suggest I should do now? Drop __iomem
> > from the structure's payload field but keep all local variables and
> > function arguments with __iomem ?
> 
> > > > +struct scmi_chan_info {
> > > > +       void *payload;
> > > > +       struct device *dev;
> > > > +       struct scmi_handle *handle;
> > > > +       void *transport_info;
> > > > +};
> > >
> > > Maybe you can wrap the scmi_chan_info inside of another
> > > structure that contains  the payload pointer, and use container_of
> > > to convert between them?
> >
> > We don't need to convert between the two of them, isn't it ? Are you
> > referring some other field here ?
> 
> > > It's not obvious which parts of the structure should be shared and
> > > which are transport specific.
> >
> > All transport specific information is kept in the transport specific
> > structure which is saved here in the transport_info field. Is there
> > something else that isn't clear ?
> 
> To answer all three, what I meant is that the payload pointer appears
> to be transport specific and

I am not sure if I understood the below statement properly. Is there
something missing from it ?

> should not be part of the common
> structure if there is generic way to access it.

The scmi protocol requires a block of shared memory which is
represented by struct scmi_shared_mem, and payload is this memory
block itself. This block of memory is accessed throughout driver.c
file using ioread/write commands. If payload is transport specific, so
will be those accesses, isn't it ? Are you suggesting to move all this
to mailbox.c (the transport specific file) instead ? I am sorry, but I
am not able to understand how exactly you want me to reorder code here
:(

@Sudeep: I had a question for you though. Looks like we are doing
ioremap() of this payload for every channel's tx/rx, why ? Why is the
same memory area mapped that way ? Can we just map the area once for
scmi block ?

-- 
viresh