linux-kernel - Re: [PATCH v4] staging: rtl8723bs: Use % 4096u instead of & 0xfff

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Message-ID: <0d62aab3-bd51-4739-88a4-9419cca7159a@stanley.mountain>
Date: Mon, 7 Apr 2025 10:20:36 +0300
From: Dan Carpenter <dan.carpenter@...aro.org>
To: Abraham Samuel Adekunle <abrahamadekunle50@...il.com>
Cc: gregkh@...uxfoundation.org, julia.lawall@...ia.fr,
	outreachy@...ts.linux.dev, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org, andy@...nel.org,
	david.laight.linux@...il.com
Subject: Re: [PATCH v4] staging: rtl8723bs: Use % 4096u instead of & 0xfff

On Mon, Apr 07, 2025 at 06:30:50AM +0000, Abraham Samuel Adekunle wrote:
> The sequence number is constrained to a range of [0, 4095], which
> is a total of 4096 values. The bitmask operation using `0xfff` is
> used to perform this wrap-around. While this is functionally correct,
> it obscures the intended semantic of a 4096-based wrap.
> 
> Using a modulo operation with `4096u` makes the wrap-around logic
> explicit and easier to understand. It clearly signals that the sequence
> number cycles though a range of 4096 values.
> It also makes the code robust against potential changes of the 4096
> upper limit, especially when it becomes a non power of 2 value while
> the AND(&) works solely for power of 2 values.
> 
> The use of `4096u` also guarantees that the modulo operation is performed
> with unsigned arithmetic, preventing potential issues with signed types.
> 
> Suggested-by: Andy Shevchenko <andy@...nel.org>
> Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@...il.com>
> ---
> Changes in v3:
> 	- Added more description to the commit message
> 	- Removed blank line in tag block.
> 	-  Added more patch recipients.
> Changes in v2:
> 	- Changed the commit message to a more descriptive message which
> 	makes it clear why the patch does the change.
> 	- Changed the subject title to include `4096u` to show that an unsigned
> 	module is used.
> Changes in v1:
> 	- Added more patch recipients.
> 
>  drivers/staging/rtl8723bs/core/rtw_xmit.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/staging/rtl8723bs/core/rtw_xmit.c b/drivers/staging/rtl8723bs/core/rtw_xmit.c
> index 297c93d65315..f534bf2448c3 100644
> --- a/drivers/staging/rtl8723bs/core/rtw_xmit.c
> +++ b/drivers/staging/rtl8723bs/core/rtw_xmit.c
> @@ -943,7 +943,7 @@ s32 rtw_make_wlanhdr(struct adapter *padapter, u8 *hdr, struct pkt_attrib *pattr
>  
>  			if (psta) {
>  				psta->sta_xmitpriv.txseq_tid[pattrib->priority]++;
> -				psta->sta_xmitpriv.txseq_tid[pattrib->priority] &= 0xFFF;
> +				psta->sta_xmitpriv.txseq_tid[pattrib->priority] &= 4096u;

You forgot to change the & to %.

regards,
dan carpenter