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

[David Laight <david.laight.linux@gmail.com>]

On Mon, 7 Apr 2025 08:53:30 +0200
Greg KH <gregkh@linuxfoundation.org> wrote:

> 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.

It is still wrong '& 0xfff' => '% 4096u'.
But it is all rather pointless especially if you can't test it.

Plausibly more useful would be to find ALL of the uses of 0xfff/4096 (I suspect
there is an array lurking somewhere) and change them to use the same constant.
But you need to be able to test the changes - or at least discover that
they make absolutely no difference to the generated object code.

	David

> 
> thanks,
> 
> greg k-h