linux-kernel - Re: [PATCH v1] ACPI: LPSS: use acpi_dev_uid_match() for matching

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Date:   Wed, 25 Oct 2023 23:33:40 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Raag Jadav <raag.jadav@...el.com>
Cc:     rafael@...nel.org, len.brown@...el.com,
        mika.westerberg@...ux.intel.com, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        mallikarjunappa.sangannavar@...el.com, bala.senthil@...el.com
Subject: Re: [PATCH v1] ACPI: LPSS: use acpi_dev_uid_match() for matching _UID

On Wed, Oct 25, 2023 at 11:08:33AM +0530, Raag Jadav wrote:
> Use acpi_dev_uid_match() for matching _UID instead of treating it
> as an integer.

NAK. See below why.

...

>  static void byt_pwm_setup(struct lpss_private_data *pdata)
>  {
> -	u64 uid;
> -
>  	/* Only call pwm_add_table for the first PWM controller */
> -	if (acpi_dev_uid_to_integer(pdata->adev, &uid) || uid != 1)
> +	if (!acpi_dev_uid_match(pdata->adev, "1"))

_UID by specification is a type of _string_. Yet, that string may represent an
integer number. Now, how many variants of the strings can you imagine that may
be interpreted as integer 1? I can tell about dozens.

With your change you restricted the all possible spectre of the 1
representations to a single one. Have you checked ALL of the DSDTs
for these platforms to say 'hey, all current tables uses "1" and
this is not an issue'? Further question, will you guarantee that new
platforms on this chip won't use something different? (Not that big
issue, but will require to actively revert your change in the future).

>  		return;
>  
>  	pwm_add_table(byt_pwm_lookup, ARRAY_SIZE(byt_pwm_lookup));
> @@ -218,10 +216,8 @@ static struct pwm_lookup bsw_pwm_lookup[] = {
>  
>  static void bsw_pwm_setup(struct lpss_private_data *pdata)
>  {
> -	u64 uid;
> -
>  	/* Only call pwm_add_table for the first PWM controller */
> -	if (acpi_dev_uid_to_integer(pdata->adev, &uid) || uid != 1)
> +	if (!acpi_dev_uid_match(pdata->adev, "1"))
>  		return;

-- 
With Best Regards,
Andy Shevchenko