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From:   Leonard Crestez <leonard.crestez@nxp.com>
To:     Marco Felsch <m.felsch@pengutronix.de>,
        Anson Huang <anson.huang@nxp.com>,
        Aisheng Dong <aisheng.dong@nxp.com>
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        "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:   Thu, 26 Sep 2019 13:25:50 +0000
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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 message=
=0A=
>>>> header's function element even the API has response data, those=0A=
>>>> special APIs are defined as void function in SCU firmware, so they=0A=
>>>> 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 combination a=
s=0A=
>>> nxp would suggest.=0A=
>>=0A=
>> Could be, but I checked the current APIs, ONLY these 2 will be used in L=
inux kernel, so=0A=
>> 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 for t=
hose special=0A=
>> APIs? To avoid checking it for all the APIs called which 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=
> Adding a special api shouldn't be the right fix. Imagine if someone (not=
=0A=
> a nxp-developer) wants to add a new driver. How could he be expected to=
=0A=
> know which api he should use. The better abbroach would be to fix the=0A=
> scu-fw instead of adding quirks..=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 =0A=
documentation. 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 =0A=
to minor quirks of the calling convention also seems reasonable. Having =0A=
the low-level IPC code peek at message IDs seems like a hack; this =0A=
belong at a slightly higher level.=0A=
=0A=
In older internal trees we use a very large amount of generated wrapper =0A=
functions. This hides calling convention details from callers but is =0A=
extremely ugly and verbose.=0A=
=0A=
--=0A=
Regards,=0A=
Leonard=0A=