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Date:   Fri, 27 Sep 2019 11:06:09 +0200
From:   Marco Felsch <m.felsch@pengutronix.de>
To:     Anson Huang <anson.huang@nxp.com>
Cc:     Leonard Crestez <leonard.crestez@nxp.com>,
        Aisheng Dong <aisheng.dong@nxp.com>,
        "shawnguo@kernel.org" <shawnguo@kernel.org>,
        "s.hauer@pengutronix.de" <s.hauer@pengutronix.de>,
        "kernel@pengutronix.de" <kernel@pengutronix.de>,
        "festevam@gmail.com" <festevam@gmail.com>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        dl-linux-imx <linux-imx@nxp.com>
Subject: Re: [PATCH] firmware: imx: Skip return value check for some special
 SCU firmware APIs
Message-ID: <20190927090609.fyxdekkzrco7memt@pengutronix.de>
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Hi Anson, Leonard,

On 19-09-27 01:20, Anson Huang wrote:
> Hi, Leonard
> 
> > On 2019-09-26 1:06 PM, Marco Felsch wrote:
> > > On 19-09-26 08:03, Anson Huang wrote:
> > >>> On 19-09-25 18:07, Anson Huang wrote:
> > >>>> The SCU firmware does NOT always have return value stored in
> > >>>> message header's function element even the API has response data,
> > >>>> those special APIs are defined as void function in SCU firmware, so
> > >>>> they should be treated as return success always.
> > >>>>
> > >>>> +static const struct imx_sc_rpc_msg whitelist[] = {
> > >>>> +	{ .svc = IMX_SC_RPC_SVC_MISC, .func =
> > >>> IMX_SC_MISC_FUNC_UNIQUE_ID },
> > >>>> +	{ .svc = IMX_SC_RPC_SVC_MISC, .func =
> > >>>> +IMX_SC_MISC_FUNC_GET_BUTTON_STATUS }, };
> > >>>
> > >>> Is this going to be extended in the near future? I see some upcoming
> > >>> problems here if someone uses a different scu-fw<->kernel
> > >>> combination as nxp would suggest.
> > >>
> > >> Could be, but I checked the current APIs, ONLY these 2 will be used
> > >> in Linux kernel, so I ONLY add these 2 APIs for now.
> > >
> > > Okay.
> > >
> > >> However, after rethink, maybe we should add another imx_sc_rpc API
> > >> for those special APIs? To avoid checking it for all the APIs called which
> > may impact some performance.
> > >> Still under discussion, if you have better idea, please advise, thanks!
> > 
> > My suggestion is to refactor the code and add a new API for the this "no
> > error value" convention. Internally they can call a common function with
> > flags.
> 
> If I understand your point correctly, that means the loop check of whether the API
> is with "no error value" for every API still NOT be skipped, it is just refactoring the code,
> right?

How makes this things easier?

> > > Adding a special api shouldn't be the right fix. Imagine if someone
> > > (not a nxp-developer) wants to add a new driver. How could he be
> > > expected to know which api he should use. The better abbroach would be
> > > to fix the scu-fw instead of adding quirks..
> 
> Yes, fixing SCU FW is the best solution, but we have talked to SCU FW owner, the SCU
> FW released has been finalized, so the API implementation can NOT be changed, but
> they will pay attention to this issue for new added APIs later. That means the number
> of APIs having this issue a very limited.

This means those APIs which already have this bug will not be fixed?
IMHO this sounds a bit weird since this is a changeable peace of code ;)

> > Right now developers who want to make SCFW calls in upstream need to
> > define the message struct in their driver based on protocol documentation.
> > This includes:
> > 
> > * Binary layout of the message (a packed struct)
> > * If the message has a response (already a bool flag)
> > * If an error code is returned (this patch adds support for it)

Why should I specify if a error code is returned?

Regards,
  Marco

> > Since callers are already exposed to the binary protocol exposing them to
> > minor quirks of the calling convention also seems reasonable. Having the
> > low-level IPC code peek at message IDs seems like a hack; this belong at a
> > slightly higher level.
> 
> A little confused, so what you suggested is to add make the imx_scu_call_rpc()
> becomes the "slightly higher level" API, then in this API, check the message IDs
> to decide whether to return error value, then calls a new API which will have
> the low-level IPC code, the this new API will have a flag passed from imx_scu_call_rpc()
> function, am I right?
> 
> Anson

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