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

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Message-ID: <3ff94d4b-7585-d7ed-9736-ba4c02b3fcff@linaro.org>
Date:   Tue, 5 Sep 2023 08:32:31 +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 04:46, wangweidong.a@...nic.com wrote:
> Thank you very much for the proposed patch, but I have some 
> questions that I would like to discuss with you
> 
> On Mon, Sep 04, 2023 at 12:53 PM +0200, Krzysztof Kozlowski wrote:
>> The Devicetree sound-channel property was never accepted and is not
>> allowed by bindings.  It is not used by any upstream user, thus
>> considering that it was never documented, should be dropped.
> 
> This node property is intended for use with multiple PA, to
> load different configurations for different PA.
> Can I add this sound-channel in the "awinic,aw88395.yaml" file?

Maybe?

> 
>> 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.


Best regards,
Krzysztof