linux-kernel - Re: [PATCH 3/3] ASoC: aw88395: drop undocumented and unused sound-channel property

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Message-ID: <537821c6-df3f-6946-b7dc-07ba9db9d416@linaro.org>
Date:   Tue, 5 Sep 2023 09:28:08 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     wangweidong.a@...nic.com
Cc:     alsa-devel@...a-project.org, broonie@...nel.org,
        lgirdwood@...il.com, linux-kernel@...r.kernel.org, perex@...ex.cz,
        tiwai@...e.com, yijiangtao@...nic.com
Subject: Re: [PATCH 3/3] ASoC: aw88395: drop undocumented and unused
 sound-channel property

On 05/09/2023 09:13, wangweidong.a@...nic.com wrote:
> Thank you very much for your reply.
> 
> On 05/09/2023 15:05, krzysztof.kozlowski@...aro.org wrote:
>> On 05/09/2023 04:46, wangweidong.a@...nic.com wrote:
> 
>>>> Even though it does not look like from the diff, the property is not
>>>> actually used by the driver, because once set, it is read only in loops
>>>> depending on ddt_num (prof_hdr->ddt_num, cfg_hdr->ddt_num).  The
>>>> variable ddt_num is never set and is always 0, so the loops do not have
>>>> any iteration.  Dropping sound-channel and ddt_num-related loops allows
>>>> to drop empty functions which in turn drop quite a lot of code.  This
>>>> entire code was not possible to execute. 
>>>
>>> The ddt_num variable is not always 0, this variable is defined
>>> in the configuration file. The "prof_hdr" variable is assigned by 
>>> the "cfg_hdr" variable. The "cfg_hdr" variable is assigned by "aw_cfg"
>>> aw_cfg is the data obtained through request_firmware.The specific 
>>> process is as follows:
>>>
>>> request_firmware ---> cont->data ---> aw_cfg->data --> cfg_hdr --> prof_hdr
> 
>> Hm. So you load user-space provided file and assign it directly, without
>> any validation (aw88395_dev_load_acf_check() checks only for magic), to
>> a kernel structure. Sounds bullet-proof. Why using known kernel
>> interfaces, better to implement some conf-file-parsing.
> 
> Could you please tell me what known kernel interfaces 
> can be used to parse files? 

With exception of Audio topology and FDT, I do not think we parse
user-provided files in Linux kernel.

Best regards,
Krzysztof