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@xxxxxxxxxxxxxxxxxxx> 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.
I count only 5 of the bits being used, not 7. (See Figure 9-4 in
section 9.4.5 of the USB-3.1 spec.) Maybe you're thinking of Feature
flags rather than Status bits? They do have a lot of overlap.
Dave Brownell wrote that code initially, so we'll never know why he
included the cast. My guess is the same as Linus's: It's there to alert
the reader that a 16-bit value is being shortened to squeeze into an
8-bit slot.
> 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.
Note that there's an out-of-date comment line just above this part of
the code:
* device: remote wakeup, selfpowered
Thanks to USB-3 support, the device recipient now defines three more
bits in devstatus: LTM_ENABLED, U1_ENABLED, and U2_ENABLED.
Alan Stern
