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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-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:   Mon, 30 Sep 2019 07:28:54 +0000
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On 2019-09-27 4:20 AM, 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=
There would be no "loop" anywhere: the responsibility would fall on the =0A=
call to call the right RPC function. In the current layering scheme =0A=
(drivers -> RPC -> mailbox) the RPC layer treats all calls the same and =0A=
it's up the the caller to provide information about calling convention.=0A=
=0A=
An example implementation:=0A=
* Rename imx_sc_rpc_call to __imx_sc_rpc_call_flags=0A=
* Make a tiny imx_sc_rpc_call wrapper which just converts resp/noresp to =
=0A=
a flag=0A=
* Make get button status call __imx_sc_rpc_call_flags with the =0A=
_IMX_SC_RPC_NOERROR flag=0A=
=0A=
Hope this makes my suggestion clearer? Pushing this to the caller is a =0A=
bit ugly but I think it's worth preserving the fact that the imx rpc =0A=
core treats services in an uniform way.=0A=
=0A=
>>> Adding a special api shouldn't be the right fix. Imagine if someone=0A=
>>> (not a nxp-developer) wants to add a new driver. How could he be=0A=
>>> expected to know which api he should use. The better abbroach would be=
=0A=
>>> to fix the scu-fw instead of adding quirks..=0A=
> =0A=
> Yes, fixing SCU FW is the best solution, but we have talked to SCU FW own=
er, the SCU=0A=
> FW released has been finalized, so the API implementation can NOT be chan=
ged, but=0A=
> they will pay attention to this issue for new added APIs later. That mean=
s the number=0A=
> of APIs having this issue a very limited.=0A=
> =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 am saying that the caller (button driver) should be responsible =0A=
for calling with a special flag which states that the RPC call.=0A=
=0A=
In internal tree this is handled inside the machine-generated function =0A=
calls, right? These are mostly skipped in upstream but maybe for these =0A=
particular calls we can manually add wrappers inside =0A=
"drivers/firmware/imx/misc.c".=0A=
=0A=
And even if the functions "return void" from a SCFW perspective it still =
=0A=
makes sense to return general kernel errors, for example from mailbox.=0A=
=0A=
--=0A=
Regards,=0A=
Leonard=0A=