linux-kernel - Re: [PATCH 1/8] mailbox: introduce ARM SMC based mailbox

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Date:   Mon, 24 Jul 2017 18:38:23 +0100
From:   Sudeep Holla <sudeep.holla@....com>
To:     Jassi Brar <jassisinghbrar@...il.com>,
        André Przywara <andre.przywara@....com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-sunxi@...glegroups.com,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>, Icenowy Zheng <icenowy@...c.xyz>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Devicetree List <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/8] mailbox: introduce ARM SMC based mailbox



On 24/07/17 18:20, Jassi Brar wrote:
> On Mon, Jul 24, 2017 at 4:50 AM, André Przywara <andre.przywara@....com> wrote:
>> On 02/07/17 06:55, Jassi Brar wrote:
>>
>>>> +       mbox_chan_received_data(link, (void *)res.a0);
>>>> +
>>> Or you can update the 'data' with value from 'a0' ?
>>
>> Mmh, I am a bit puzzled by this. Why would this be needed or useful?
>>
> I meant instead of calling mbox_chan_received_data(), simply update
> the value at 'data' with res.a0
> 
> Technically the firmware does not "send" us a message. It only updates
> the structure we share with it. So maybe we could reflect that by
> updating the data pointer the client driver asked to send.
> Also it is optional for clients to provide the rx_callback(). By
> calling mbox_chan_received_data() you mandate clients provide that
> callback.
> 
> Nothing serious, just that looking closely, updating 'data' seems a
> better option.
> 
>> I see that the SCPI firmware driver (as the user of the mailbox API) is
>> expecting the return value from a0 as returned above, translating the
>> firmware error codes into Linux' ones.
>>
> I am afraid, SCPI driver is not the golden example for client drivers
> to follow. It is supposed to work only with MHU, and then, it is
> likely to break if some other protocol is running parallel to it.
> 

Not sure why do you say it works only with ARM MHU ? AmLogic uses it
with their mailbox driver. However they followed an interim version of
the SCPI spec which is termed "legacy" in the driver.
-- 
Regards,
Sudeep