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

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Date:   Tue, 14 Jan 2020 10:56:16 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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 Tue, Jan 14, 2020 at 10:26 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> 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:
> >
> > 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
> :(

My point was that you cannot mix __iomem accesses with pointer
accesses. As I understood it, the current version uses a pointer to a
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.

     Arnd