[PATCH v3] staging: rtl8723bs: Use % 4096u instead of & 0xfff

[PATCH v3] staging: rtl8723bs: Use % 4096u instead of & 0xfff

[Abraham Samuel Adekunle]

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.

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@kernel.org>
David Laight <david.laight.linux@gmail.com>

Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>
---
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;
 				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;
 
 						pattrib->ampdu_en = true;/* AGG EN */
 					} else {
-						psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (pattrib->seqnum+1)&0xfff;
+						psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (pattrib->seqnum+1)&4096u;
 						pattrib->ampdu_en = true;/* AGG EN */
 					}
 				}
-- 
2.34.1

Re: [PATCH v3] staging: rtl8723bs: Use % 4096u instead of & 0xfff

[Andy Shevchenko]

On Mon, Apr 7, 2025 at 3:27 AM Abraham Samuel Adekunle
<abrahamadekunle50@gmail.com> 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.
>
> The use of `4096u` also guarantees that the modulo operation is performed
> with unsigned arithmetic, preventing potential issues with signed types.

Also there are a couple of important things about modulo vs. AND:

The modulo use for wrapping around is making code robust against
potential changes of the upper range, especially when it becomes
non-power-of-2 value, the AND works solely for power-of-2 values. The
modulo in case of power-of-2 is optimised by the compiler to the same
or equivalent code.

> Suggested-by: Andy Shevchenko <andy@kernel.org>
> David Laight <david.laight.linux@gmail.com>

Not sure what tag David's name is meant for.

>

This blank line shouldn't be here. It's a tag block where we don't put
blank lines.

> Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>

-- 
With Best Regards,
Andy Shevchenko

Re: [PATCH v3] staging: rtl8723bs: Use % 4096u instead of & 0xfff

[Greg Kroah-Hartman]

On Mon, Apr 07, 2025 at 12:27:53AM +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.
> 
> 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@kernel.org>
> David Laight <david.laight.linux@gmail.com>
> 
> Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>
> ---
> 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 +++---

Any specific reason you did not include the staging mailing list like
scripts/get_maintainers.pl asks you to?

thanks,

greg k-h

Re: [PATCH v3] staging: rtl8723bs: Use % 4096u instead of & 0xfff

[Samuel Abraham]

On Mon, Apr 7, 2025 at 6:10 AM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Mon, Apr 07, 2025 at 12:27:53AM +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.
> >
> > 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@kernel.org>
> > David Laight <david.laight.linux@gmail.com>
> >
> > Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>
> > ---
> > 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 +++---
>
> Any specific reason you did not include the staging mailing list like
> scripts/get_maintainers.pl asks you to?

Thank you, Greg.
I have sent an updated patch.

Adekunle