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

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Message-ID: <Y1Vjb9v2ggSjhRbc@kroah.com>
Date:   Sun, 23 Oct 2022 17:53:19 +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 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.

Although if we ever do get another 2 status bits defined, this code will
break so we probably should do that too.

I'll go do that for a v2 of this and properly comment it.

> I suspect a comment would be more readable than an odd cast that
> doesn't actually change anything (since the assignment does it
> anyway).
> 
> Or maybe people wrote it that way on purpose, and used that variable
> name on purpose.
> 
> Because 'dum' is Swedish for 'stupid', and maybe there's a coded
> message in that driver?

That whole driver is called "dummy" as it's a "fake" driver, not a
"stupid" one :)

thanks,

greg k-h