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

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Message-ID: <VI1PR04MB702397C54519DC27CFF05A78EE810@VI1PR04MB7023.eurprd04.prod.outlook.com>
Date:   Fri, 27 Sep 2019 11:22:22 +0000
From:   Leonard Crestez <leonard.crestez@....com>
To:     Marco Felsch <m.felsch@...gutronix.de>,
        Anson Huang <anson.huang@....com>
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

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