drivers/staging/rtl8723bs/core/rtw_xmit.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
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 `% 4096u` makes the wrap-around logic
explicit and easier to understand. It clearly signals that the
sequence number cycles through 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
the signed types.
Suggested-by: Andy Shevchenko <andy@kernel.org>
Suggested-by: David Laight <david.laight.linux@gmail.com>
Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@gmail.com>
---
Changes in v4:
- Corrected patch to use '%' instead of '&'
- To ensure this change does not affect the functional
behaviour, I compared the generated object files before and
after the change using the `cmp` which compares the two
object files byte by byte as shown below:
$ make drivers/staging/rtl8723bs/core/rtw_xmit.o
$ cmp rtw_xmit_before.o rtw_xmit_after.o
No differences were found in the output, confirming that the
change does not alter the compiled output.
Changes in v3:
- Added more description to the commit message.
- Removed blank line in the tag block.
- Added more patch recipients.
Changes in v2:
- Changed the commit message t 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 026061b464f7..548fcf9968bd 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 */
}
}
--
2.34.1On Mon, Apr 7, 2025 at 6:54 PM 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 `% 4096u` makes the wrap-around logic > explicit and easier to understand. It clearly signals that the > sequence number cycles through 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 > the signed types. ... > - psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (tx_seq+1)&0xfff; > + psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (tx_seq+1)%4096u; > - psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (pattrib->seqnum+1)&0xfff; > + psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (pattrib->seqnum+1)%4096u; To reduce churn, it would be nice to have another patch _before_ this one that makes above clearer (by adding spaces) as we already new in practice that it's hard to read: So, this will become two lines in each of the cases, and in this patch only one of those line will be touched. ... Besides that I haven't found in the changelog if you have looked at the entire driver code and checked that all usages of this field is done in the same / similar way and no need to convert anything more that these. -- With Best Regards, Andy Shevchenko
On Mon, Apr 7, 2025 at 5:17 PM Andy Shevchenko <andy.shevchenko@gmail.com> wrote: > > On Mon, Apr 7, 2025 at 6:54 PM 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 `% 4096u` makes the wrap-around logic > > explicit and easier to understand. It clearly signals that the > > sequence number cycles through 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. > > > ... > > Besides that I haven't found in the changelog if you have looked at > the entire driver code and checked that all usages of this field is > done in the same / similar way and no need to convert anything more > that these. I have found more cases using a small Coccinelle semantic patch. There were also cases in the media driver, but I did not touch those since it is not allowed for an outreachy applicant. I will send a patchset soon. Thanks Adekunle
On Mon, Apr 7, 2025 at 5:17 PM Andy Shevchenko <andy.shevchenko@gmail.com> wrote: > > On Mon, Apr 7, 2025 at 6:54 PM 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 `% 4096u` makes the wrap-around logic > > explicit and easier to understand. It clearly signals that the > > sequence number cycles through 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 > > the signed types. > > ... > > > - psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (tx_seq+1)&0xfff; > > + psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (tx_seq+1)%4096u; > > > - psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (pattrib->seqnum+1)&0xfff; > > + psta->BA_starting_seqctrl[pattrib->priority & 0x0f] = (pattrib->seqnum+1)%4096u; > > To reduce churn, it would be nice to have another patch _before_ this > one that makes above clearer (by adding spaces) as we already new in > practice that it's hard to read: > So, this will become two lines in each of the cases, and in this patch > only one of those line will be touched. Okay, I will send a patchset for the change. The first one will add the spaces, then the second one will add the logic, and they can be applied in sequence. > > ... > > Besides that I haven't found in the changelog if you have looked at > the entire driver code and checked that all usages of this field is > done in the same / similar way and no need to convert anything more > that these. No, I have not checked other drivers. I will write a semantic patch to match and transform such cases Thanks Adekunle.
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