linux-kernel - Re: [PATCH] iio: imu: adis16550: rework clock range test

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Message-ID: <6f6d51de-7c7e-48a5-86b8-c1a77f51ab4f@baylibre.com>
Date: Wed, 2 Jul 2025 10:48:08 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
 Andy Shevchenko <andriy.shevchenko@...el.com>
Cc: Lars-Peter Clausen <lars@...afoo.de>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Jonathan Cameron <jic23@...nel.org>, Nuno Sá
 <nuno.sa@...log.com>, Robert Budai <robert.budai@...log.com>,
 Andy Shevchenko <andy@...nel.org>, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: imu: adis16550: rework clock range test

On 7/2/25 10:31 AM, Jonathan Cameron wrote:
> On Wed, 2 Jul 2025 18:17:24 +0300
> Andy Shevchenko <andriy.shevchenko@...el.com> wrote:
> 
>> On Wed, Jul 02, 2025 at 10:07:17AM -0500, David Lechner wrote:
>>> On 7/2/25 9:59 AM, Andy Shevchenko wrote:  
>>>> On Wed, Jul 02, 2025 at 05:53:57PM +0300, Andy Shevchenko wrote:  
>>>>> On Wed, Jul 02, 2025 at 09:27:45AM -0500, David Lechner wrote:  
>>>>>> Rework the clock rate range test to test if sync_mode_data != NULL
>>>>>> instead of testing if the for loop index variable. This makes it easier
>>>>>> for static analyzers to see that we aren't using an uninitialized
>>>>>> sync_mode_data [1].  
>>>>>
>>>>> But at the same time it makes it not to be the usual pattern.,,  
>>>>
>>>> Reading the static analyser output I think the first hunk is only what we need,
>>>> but this is still false positive and it's problem of that static
>>>> analyser. Have you filed a bug there? (My point is that modifying the code for
>>>> the advantage of false positives of some static analyser is wrong road to go
>>>> in my opinion.)  
>>>
>>> I agree that we shouldn't fix this _only_ to make the static analyzer
>>> happy. But I had to think quite a bit harder to see that the existing
>>> code was correct compared to what I have proposed here.
>>>
>>> But if this is a common pattern that I just haven't learned to identify
>>> at a glance yet and everybody else can easily see that the existing code
>>> is correct, then perhaps it isn't worth the change.  
>>
>> To me checking against index variable (when it's integer, obviously) is correct
>> thing to do and regular pattern. OTOH, if the "index" is a pointer and rather
>> we call it "iterator", the angle of view is different because in some cases
>> it may lead to stale or invalid value which might be mistakenly dereferenced or
>> speculated (see more in the discussion about list entry APIs [entry is a
>> keyword here] and if list_entry_is_head() is a good approach.)
>>
> 
> Original code looks fine to me and is a very common pattern.  So I'd argue
> the static analyzer needs some work.
> 
> Jonathan

OK, we can drop the patch.