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Message-ID: <f768cfec-d20d-424d-85ef-3576434aca12@quicinc.com>
Date: Wed, 13 Mar 2024 11:04:44 -0700
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Subject: Re: [PATCH v4 01/12] wifi: ath12k: add multiple radio support in a
 single MAC HW un/register
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To: Kalle Valo <kvalo@kernel.org>
CC: Rameshkumar Sundaram <quic_ramess@quicinc.com>,
        <ath12k@lists.infradead.org>, <linux-wireless@vger.kernel.org>,
        "Karthikeyan
 Periyasamy" <quic_periyasa@quicinc.com>
References: <20240312135557.1778379-1-quic_ramess@quicinc.com>
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 <87il1qf571.fsf@kernel.org> <87edcef4qi.fsf@kernel.org>
From: Jeff Johnson <quic_jjohnson@quicinc.com>
In-Reply-To: <87edcef4qi.fsf@kernel.org>
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On 3/13/2024 9:58 AM, Kalle Valo wrote:
> Kalle Valo <kvalo@kernel.org> writes:
> 
>> Jeff Johnson <quic_jjohnson@quicinc.com> writes:
>>
>>> On 3/13/2024 5:57 AM, Rameshkumar Sundaram wrote:
>>>> On 3/13/2024 3:23 AM, Jeff Johnson wrote:
>>>>> and guess we have to figure out how to suppress the ath12k-check issues with
>>>>> this macro
>>>> ath12k-check complains about the reuse of ah and index arguments which 
>>>> may get evaluated multiple times if its an arithmetic expression, But 
>>>> areas where we use the macro in our code aren't doing so.
>>>> Do you have any suggestions here ? or shall we go back and use this 
>>>> for-loop inline.
>>>
>>> The macro makes sense -- we'll need to update the overrides in ath12k-check.
>>
>> IIRC it is possible to avoid variable reuse in macros with typeof()
>> operator (or something like that). I can't remember the details right
>> now but I think there are examples in the kernel code.
> 
> Here's the GCC documentation with an example:
> 
> https://gcc.gnu.org/onlinedocs/gcc/Typeof.html
> 

the problem here is that the macro actually writes to those arguments multiple
times, so we actually need to reuse the arguments

the macro as defined exactly matches the semantics of other for_each macros in
the kernel, i.e. see in include/linux/list.h:
#define list_for_each(pos, head) \
	for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)

what I don't understand is why list_for_each() doesn't trigger the same
checkpatch issues. even stranger is that if I copy that macro into ath12k then
I do see the same checkpatch issues:
CHECK: Macro argument reuse 'pos' - possible side-effects?
#998: FILE: drivers/net/wireless/ath/ath12k/core.h:998:
+#define list_for_each(pos, head) \
+       for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)

CHECK: Macro argument reuse 'head' - possible side-effects?
#998: FILE: drivers/net/wireless/ath/ath12k/core.h:998:
+#define list_for_each(pos, head) \
+       for (pos = (head)->next; !list_is_head(pos, (head)); pos = pos->next)

So I'm really confused since I don't see anything in checkpatch.pl that would
cause the behavior to change between macros in include/linux/list.h vs macros
in drivers/net/wireless/ath/ath12k/core.h

<scratch head>

/jeff