linux-kernel - Re: [PATCH v5 2/8] firmware: add support for ARM System Control and Power Interface(SCPI) protocol

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Message-ID: <55BB4274.2050905@arm.com>
Date:	Fri, 31 Jul 2015 10:40:04 +0100
From:	Sudeep Holla <sudeep.holla@....com>
To:	Jassi Brar <jassisinghbrar@...il.com>
CC:	Sudeep Holla <sudeep.holla@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Punit Agrawal <Punit.Agrawal@....com>,
	"Jon Medhurst (Tixy)" <tixy@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Arnd Bergmann <arnd@...db.de>, Olof Johansson <olof@...om.net>,
	Kevin Hilman <khilman@...nel.org>
Subject: Re: [PATCH v5 2/8] firmware: add support for ARM System Control and
 Power Interface(SCPI) protocol



On 30/07/15 18:56, Jassi Brar wrote:
> On Wed, Jul 29, 2015 at 6:20 PM, Sudeep Holla <sudeep.holla@....com> wrote:
>> On 29/07/15 12:19, Jassi Brar wrote:
>>
>>> Assuming the former, let me explain. When a client receives a
>>> response, it can be sure that the request has already been read by the
>>> remote.
>>
>> Waiting for the response would be too late for few expensive commands
>> (e.g setting up external regulators). The remote firmware acknowledges
>> Tx by setting status flags and will be ready to accept new commands.
>>
> No. Polling still happens. If anything, mbox_client_txdone() should
> only speed up things.
>
>>> If the protocol specifies every request has some response, the
>>
>> Not always true there can be few commands without response. The protocol
>> specifies that we need check the status flag before sending the new
>> command as it's bidirectional, hence polling is recommended (Section 2.2
>> Communication flow in the SCPI specification)
>>
> mbox_client_txdone() will only be called for commands that has some
> response. Commands that don't have a response would be completed by
> polling.
>

I forgot to mention, we have a the following description in
mbox_client_txdone which is misleading:

"The client/protocol had received some 'ACK' packet and it notifies the
API that the last packet was sent successfully. This only works if the
controller can't sense TX-Done."

which is clearly not the case in SCPI. IMO we may have to reword that.

Regards,
Sudeep
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