linux-kernel - Re: [PATCH V1 3/3] ASoC: codecs: Add aw87390 amplifier driver

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Date:   Mon, 4 Sep 2023 15:02:31 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Mark Brown <broonie@...nel.org>
Cc:     wangweidong.a@...nic.com, lgirdwood@...il.com, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, conor+dt@...nel.org,
        perex@...ex.cz, tiwai@...e.com, rf@...nsource.cirrus.com,
        herve.codina@...tlin.com, shumingf@...ltek.com,
        rdunlap@...radead.org, 13916275206@....com, ryans.lee@...log.com,
        linus.walleij@...aro.org, ckeepax@...nsource.cirrus.com,
        yijiangtao@...nic.com, liweilei@...nic.com, colin.i.king@...il.com,
        trix@...hat.com, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        zhangjianming@...nic.com
Subject: Re: [PATCH V1 3/3] ASoC: codecs: Add aw87390 amplifier driver

On 04/09/2023 14:30, Mark Brown wrote:
> On Mon, Sep 04, 2023 at 02:17:43PM +0200, Krzysztof Kozlowski wrote:
>> On 04/09/2023 13:46, wangweidong.a@...nic.com wrote:
> 
>>> +	ret = regmap_read(regmap, AW87390_ID_REG, &chip_id);
>>> +	if (ret) {
>>> +		dev_err(&i2c->dev, "%s read chipid error. ret = %d\n", __func__, ret);
>>> +		return ret;
>>> +	}
> 
>>> +	if (chip_id != AW87390_CHIP_ID) {
>>> +		dev_err(&i2c->dev, "unsupported device\n");
> 
>> Why? The compatible tells it cannot be anything else.
> 
> This is very common good practice, as well as validating communication

No, it is neither common nor good. The kernel's job is not to verify the
supplied DTS. Rob also made here a point:

https://lore.kernel.org/all/CAL_Jsq+wcrOjh7+0c=mrg+Qz6dbhOUE-VEeQ4FoWC3Y7ENoyfQ@mail.gmail.com/

> with the device it verifies that the device descrbied in the DT is the
> one that is actually present in the system.  This might create hassle
> down the line if there is a backwards compatible upgrade but that's much
> rarer for this class of hardware than cut'n'pasting of device trees.

Best regards,
Krzysztof