Re: [PATCH] staging: rtl8723bs: Replace `& 0xfff` with `% 4096u`

[Samuel Abraham]

On Mon, Apr 14, 2025 at 10:00 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, Apr 14, 2025 at 08:38:53AM +0100, Samuel Abraham wrote:
> > On Mon, Apr 14, 2025 at 8:23 AM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Wed, Apr 09, 2025 at 06:48:02PM +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 `% 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.
> > > >
> > > > Found by Coccinelle.
> > > >
> > > > Suggested by Andy Shevchenko <andy@xxxxxxxxxx>
> > > > Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@xxxxxxxxx>
> > > > ---
> > > > Coccinelle semantic patch used to find cases:
> > > > @@
> > > > expression e;
> > > >
> > > > @@
> > > > * e & 0xfff
> > > >
> > > > 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.
> > >
> > > This is version 11, right?  What happened to the list of previous
> > > versions and what changed down here?
> > >
> > > confused,
> >
> > Hello Greg,
> >
> > I collapsed this patch to the previous patchset I had worked on that
> > made the same changes to the same driver.
> > So this patch was collapsed into PATCH v10, which is the last version
> > for this change.
> >
> > The change log in "[PATCH v10 0/2] staging: rtl8723bs: Improve
> > readability and clarity of sequence number wrapping" explains this.
> > This patch was collapsed into patch 2 of this patchset.
>
> Think about it from my side.  I get hundreds of patches each day to
> review.  If I see a v10 and then a patch with no version at all, what am
> I supposed to do?  I would assume something went really wrong and just
> delete this "obviously old" version as it would have been the first
> version of the patch, especially as there was no version information
> below the --- line.
>
> So, what would you do in my situation?  What would you want to see if
> you were in my situation?
>
> thanks,

I am so sorry for causing this confusion. It was not intended.
PATCH v9 was the last patchset which had all the recommended changes
implemented.

Later on, I proceeded to check for more cases in the codebase so I
could make the same change.
I then saw more changes and sent the patch independently (Which is
where I made the mistake).
However, it was suggested that since this new patch was making the
same change in the same driver as PATCH v9,
I should incorporate it into the initial change. This was why I
collapsed the change and made PATCH v10.

I'm sorry once again.

Adekunle.