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From:   Leonard Crestez <leonard.crestez@nxp.com>
To:     Anson Huang <anson.huang@nxp.com>,
        Marco Felsch <m.felsch@pengutronix.de>,
        Aisheng Dong <aisheng.dong@nxp.com>
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        <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
Thread-Topic: [PATCH] firmware: imx: Skip return value check for some special
 SCU firmware APIs
Thread-Index: AQHVc4lSn4nBMGf230anvZh0PllY6g==
Date:   Fri, 27 Sep 2019 11:16:24 +0000
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On 27.09.2019 04:20, Anson Huang wrote:=0A=
>> On 2019-09-26 1:06 PM, Marco Felsch wrote:=0A=
>>> On 19-09-26 08:03, Anson Huang wrote:=0A=
>>>>> On 19-09-25 18:07, Anson Huang wrote:=0A=
>>>>>> The SCU firmware does NOT always have return value stored in=0A=
>>>>>> message header's function element even the API has response data,=0A=
>>>>>> those special APIs are defined as void function in SCU firmware, so=
=0A=
>>>>>> they should be treated as return success always.=0A=
>>>>>>=0A=
>>>>>> +static const struct imx_sc_rpc_msg whitelist[] =3D {=0A=
>>>>>> +	{ .svc =3D IMX_SC_RPC_SVC_MISC, .func =3D=0A=
>>>>> IMX_SC_MISC_FUNC_UNIQUE_ID },=0A=
>>>>>> +	{ .svc =3D IMX_SC_RPC_SVC_MISC, .func =3D=0A=
>>>>>> +IMX_SC_MISC_FUNC_GET_BUTTON_STATUS }, };=0A=
>>>>>=0A=
>>>>> Is this going to be extended in the near future? I see some upcoming=
=0A=
>>>>> problems here if someone uses a different scu-fw<->kernel=0A=
>>>>> combination as nxp would suggest.=0A=
>>>>=0A=
>>>> Could be, but I checked the current APIs, ONLY these 2 will be used=0A=
>>>> in Linux kernel, so I ONLY add these 2 APIs for now.=0A=
>>>=0A=
>>> Okay.=0A=
>>>=0A=
>>>> However, after rethink, maybe we should add another imx_sc_rpc API=0A=
>>>> for those special APIs? To avoid checking it for all the APIs called w=
hich=0A=
>> may impact some performance.=0A=
>>>> Still under discussion, if you have better idea, please advise, thanks=
!=0A=
>>=0A=
>> My suggestion is to refactor the code and add a new API for the this "no=
=0A=
>> error value" convention. Internally they can call a common function with=
=0A=
>> flags.=0A=
> =0A=
> If I understand your point correctly, that means the loop check of whethe=
r the API=0A=
> is with "no error value" for every API still NOT be skipped, it is just r=
efactoring the code,=0A=
> right?=0A=
=0A=
>> Right now developers who want to make SCFW calls in upstream need to=0A=
>> define the message struct in their driver based on protocol documentatio=
n.=0A=
>> This includes:=0A=
>>=0A=
>> * Binary layout of the message (a packed struct)=0A=
>> * If the message has a response (already a bool flag)=0A=
>> * If an error code is returned (this patch adds support for it)=0A=
>>=0A=
>> Since callers are already exposed to the binary protocol exposing them t=
o=0A=
>> minor quirks of the calling convention also seems reasonable. Having the=
=0A=
>> low-level IPC code peek at message IDs seems like a hack; this belong at=
 a=0A=
>> slightly higher level.=0A=
> =0A=
> A little confused, so what you suggested is to add make the imx_scu_call_=
rpc()=0A=
> becomes the "slightly higher level" API, then in this API, check the mess=
age IDs=0A=
> to decide whether to return error value, then calls a new API which will =
have=0A=
> the low-level IPC code, the this new API will have a flag passed from imx=
_scu_call_rpc()=0A=
> function, am I right?=0A=
=0A=
No, I mean there should be no loop enumerating svc/func ids: *the caller =
=0A=
should know* that it's calling a func which doesn't return an error code =
=0A=
and call a different variant of imx_scu_call_rpc=0A=
=0A=
Maybe add an internal __imx_scu_call_rpc_flags and turn the current =0A=
imx_scu_call_rpc into a wrapper.=0A=
=0A=
--=0A=
Regards,=0A=
Leonard=0A=