linux-kernel - Re: [PATCH] USB: gadget: dummy

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Message-ID: <Y1VmBuVrkL7MSzjY@kroah.com>
Date:   Sun, 23 Oct 2022 18:04:22 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Alan Stern <stern@...land.harvard.edu>
Cc:     linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        Felipe Balbi <balbi@...nel.org>,
        Jakob Koschel <jakobkoschel@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>
Subject: Re: [PATCH] USB: gadget: dummy_hcd: switch char * to u8 *

On Sun, Oct 23, 2022 at 05:53:19PM +0200, Greg Kroah-Hartman wrote:
> On Fri, Oct 21, 2022 at 10:30:37AM -0700, Linus Torvalds wrote:
> > On Thu, Oct 20, 2022 at 11:44 PM Greg Kroah-Hartman
> > <gregkh@...uxfoundation.org> wrote:
> > >
> > > The function handle_control_request() casts the urb buffer to a char *,
> > > and then treats it like a unsigned char buffer when assigning data to
> > > it.  On some architectures, "char" is really signed, so let's just
> > > properly set this pointer to a u8 to take away any potential problems as
> > > that's what is really wanted here.
> > 
> > I think you might as well also remove the cast that was always a bit odd:
> > 
> >                 buf[0] = (u8)dum->devstatus;
> > 
> > although maybe it's intentional ("look, ma, I'm truncating this
> > value") because 'devstatus' is a 'u16' type?
> 
> (adding Alan as he's the owner of this file now)
> 
> Yes, devstatus is a u16 as that's what the USB spec says it should be,
> but so far only 7 of the lower bits have been used.  I guess to do this
> properly we should also copy the upper 8 bits in to buf[1], eventhough
> in reality it's only ever going to be 0x00 for now.

Along these lines, do we really not have a predefined macro/inline
function that does:
	(value >> 8)
to give you the "high byte" of a 16bit value?  I keep seeing people
write their own macros for this in staging drivers, but I just
attributed that to them not using the correct in-kernel macro, but I
can't seem to find anything at the moment to do this (same with "give me
just the lower 8 bits of a 16bit value").

Am I just blind?

It's not like it's complex or tricky stuff, I just thought we had
something in bits.h or bitops.h or the like.  Oh well...

thanks,

greg k-h