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

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Message-ID: <2025040752-unrefined-labored-8c8c@gregkh>
Date: Mon, 7 Apr 2025 08:53:30 +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 08:36:35AM +0200, Greg KH wrote:
> 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...)

Sorry, no, I was wrong, it is being & here, but not %.  My fault,
the lack of spaces here threw me.

thanks,

greg k-h