linux-kernel - RE: [PATCH] firmware: imx: Skip return value check for some special SCU firmware APIs

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Date:   Sun, 29 Sep 2019 01:12:57 +0000
From:   Anson Huang <anson.huang@....com>
To:     Leonard Crestez <leonard.crestez@....com>,
        Marco Felsch <m.felsch@...gutronix.de>
CC:     Aisheng Dong <aisheng.dong@....com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] firmware: imx: Skip return value check for some special
 SCU firmware APIs

Hi, Leonard/Marco
	I think we should get aligned first, my original thought is to let SCU API caller NOT aware of those special APIs, so have to do the special handling in imx_scu_call_rpc(). And the short loop check has to be used which would impact the performance a little bit I think. But Leonard stated the caller should know the SCU FW API's usage, if so, then I think the special callers can just skip the return value check, adding a comment to describe the reason, would it be much more easier than changing the imx_scu_call_rpc()? Or any other suggestion?

Anson

> On 27.09.2019 12:06, Marco Felsch wrote:
> > 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.
> >>
> >>>> 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
> > ;)
> 
> It's not a bug, it's a documented feature ;)
> 
> >>> 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?
> 
> Because you're already defining the message struct and you're already
> specifying if a response is required.
> 
> The assumption is that anyone adding a SCFW call to a driver is already
> looking at SCFW documentation which describes the binary message format.
> 
> --
> Regards,
> Leonard