Re: [PATCH] usb: storage: ene_ub6250: Fix right shift warnings

Alan Stern
2024-07-31T18:20:00Z

On Wed, Jul 31, 2024 at 11:34:45PM +0530, Abhishek Tamboli wrote:
> On Wed, Jul 31, 2024 at 10:04:33AM -0400, Alan Stern wrote:
> > On Wed, Jul 31, 2024 at 11:15:28AM +0200, 'Oliver Neukum' via USB Mass Storage on Linux wrote:
> > > Hi,
> > >
> > > On 30.07.24 19:56, Abhishek Tamboli wrote:
> > > > On Tue, Jul 30, 2024 at 09:09:05AM +0200, Oliver Neukum wrote:
> > >
> > > > > 1. use a constant, where a constant is used
> > > > I think you are suggesting that I should replace hard-coded values like the
> > > > buffer size with named constants. For example:
> > > >
> > > > #define BUF_SIZE 8
> > > > unsigned char buf[BUF_SIZE];
> > >
> > > Yes, but the constant we need to look at here is bl_len.
> > > This is a variable needlessly.
> >
> > The code in ms_scsi_read_capacity() is written that way to be consistent
> > with the sd_scsi_read_capacity() routine. Or maybe it was just
> > copied-and-pasted, and then the variable's type was changed for no good
> > reason.
> >
> > Replacing the variable with a constant won't make much difference. The
> > compiler will realize that bl_len has a constant value and will generate
> > appropriate code anyway. I think just changing the type is a fine fix.
> >
> > > > > 2. use the macros for converting endianness
> > > > Can I use macros like cpu_to_le32 for converting the bl_num and bl_len values.
> > > > Should I replace all instances of manual bitwise shifts with these macros?
> > >
> > > Yes.
> > >
> > > > For example:
> > > >
> > > > u32 bl_len = 0x200;
> > > > buf[0] = cpu_to_le32(bl_num) >> 24;
> > > > buf[4] = cpu_to_le32(bl_len) >> 24;
> > > >
> > > > Is using cpu_to_le32 appropriate for the data format required by this
> > > > device?
> > >
> > > Well, the format is big endian. So, cpu_to_be32() will be required.
> >
> > Better yet, use put_unaligned_be32().
> Would you recommend submitting a follow-up patch to incorporate this change, or should I leave it as is for now.

You can submit another patch as a clean-up, if you want. But as I said,
it isn't needed.

> >However, there's nothing really
> >wrong with the code as it stands. It doesn't need to be changed now.
> As you mentioned there's no need to change the code, So my initial patch is okay as is?

It is as far as I'm concerned. Obviously Oliver has a different
opinion. But I'm the Maintainer of the usb-storage driver, so my
opinion counts for more than his does, in this case. :-)

Alan Stern