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

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Message-ID: <20200113064156.lt3xxpzygattz3he@vireshk-i7>
Date:   Mon, 13 Jan 2020 12:11:56 +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 10-01-20, 12:15, Arnd Bergmann wrote:
> On Fri, Jan 10, 2020 at 10:43 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:
> >
> > The SCMI specification is fairly independent of the transport protocol,
> > which can be a simple mailbox (already implemented) or anything else.
> > The current Linux implementation however is very much dependent of the
> > mailbox transport layer.
> >
> > This patch makes the SCMI core code (driver.c) independent of the
> > mailbox transport layer and moves all mailbox related code to a new
> > file: mailbox.c.
> >
> > We can now implement more transport protocols to transport SCMI
> > messages, some of the transport protocols getting discussed currently
> > are SMC/HVC, SPCI (built on top of SMC/HVC), OPTEE based mailbox
> > (similar to SPCI), and vitio based transport as alternative to mailbox.
> >
> > The transport protocols just need to provide struct scmi_desc, which
> > also implements the struct scmi_transport_ops.
> >
> > Signed-off-by: Viresh Kumar <viresh.kumar@...aro.org>
> > ---
> > V2:
> > - Dropped __iomem from payload data.
> 
> 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 ?

> > - Moved transport ops to scmi_desc, and that has a per transport
> >   instance now which is differentiated using the compatible string.
> > - Converted IS_ERR_OR_NULL to IS_ERR.
> 
> These look good to me.
> 
> > + * @payload: Transmit/Receive payload area
> > + * @dev: Reference to device in the SCMI hierarchy corresponding to this
> > + *      channel
> > + * @handle: Pointer to SCMI entity handle
> > + * @transport_info: Transport layer related information
> > + */
> > +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 ?

-- 
viresh