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

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Message-ID: <2025041709-brick-unplug-c155@gregkh>
Date: Thu, 17 Apr 2025 18:56:28 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Samuel Abraham <abrahamadekunle50@...il.com>
Cc: julia.lawall@...ia.fr, linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org, david.laight.linux@...il.com,
	dan.carpenter@...aro.org, andy@...nel.org
Subject: Re: [PATCH] staging: rtl8723bs: Replace `& 0xfff` with `% 4096u`

On Thu, Apr 17, 2025 at 05:33:30PM +0100, Samuel Abraham wrote:
> On Mon, Apr 14, 2025 at 10:00 AM Greg KH <gregkh@...uxfoundation.org> 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@...uxfoundation.org> 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@...nel.org>
> > > > > Signed-off-by: Abraham Samuel Adekunle <abrahamadekunle50@...il.com>
> > > > > ---
> > > > > 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?
> 
> Hello Greg, I'm sorry once again,
> Please, do I send a PATCH v11 for this change?

Yes please.

> It seems my mistake had made you delete the PATCH v10.

Yes I did.

thanks,

greg k-h