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

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Message-ID: <2025040757-clergyman-finalist-0c63@gregkh>
Date: Mon, 7 Apr 2025 08:36:35 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Abraham Samuel Adekunle <abrahamadekunle50@...il.com>
Cc: julia.lawall@...ia.fr, outreachy@...ts.linux.dev,
	linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
	dan.carpenter@...aro.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

<snip>

> -				psta->sta_xmitpriv.txseq_tid[pattrib->priority] &= 0xFFF;
> +				psta->sta_xmitpriv.txseq_tid[pattrib->priority] &= 4096u;

I do not see a modulo operation here, only another & operation.

>  				pattrib->seqnum = psta->sta_xmitpriv.txseq_tid[pattrib->priority];
>  
>  				SetSeqNum(hdr, pattrib->seqnum);
> @@ -963,11 +963,11 @@ s32 rtw_make_wlanhdr(struct adapter *padapter, u8 *hdr, struct pkt_attrib *pattr
>  					if (SN_LESS(pattrib->seqnum, tx_seq)) {
>  						pattrib->ampdu_en = false;/* AGG BK */
>  					} else if (SN_EQUAL(pattrib->seqnum, tx_seq)) {
> -						psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (tx_seq+1)&0xfff;
> +						psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (tx_seq+1)&4096u;

This also looks odd, nothing is being "AND" here, it's an address value
being set (and an odd one at that, but that's another issue...)

How was any of this tested?

Slow down, take some time, and think about what you are wanting to do
here.  There's no rush.

thanks,

greg k-h