Re: [PATCH] usb: xhci: fix incorrect memset()

[Mathias Nyman]

On 11.12.2017 19:05, Arnd Bergmann wrote:
> On Mon, Dec 11, 2017 at 6:01 PM, Greg Kroah-Hartman
> <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> > On Mon, Dec 11, 2017 at 02:59:13PM +0200, Mathias Nyman wrote:
> > > On 11.12.2017 13:27, Arnd Bergmann wrote:
> > > > gcc-8 warnings about the new driver using a memset with a bogus length:
> > > >
> > > > drivers/usb/host/xhci-dbgcap.c: In function 'xhci_dbc_eps_exit':
> > > > drivers/usb/host/xhci-dbgcap.c:369:2: error: 'memset' used with length equal to number of elements without multiplication by element size [-Werror=memset-elt-size]
> > > >
> > > > It looks like the author meant to use sizeof() rather than ARRAY_SIZE()
> > > > here, so use that.
> > > >
> > > > Fixes: dfba2174dc42 ("usb: xhci: Add DbC support in xHCI driver")
> > > > Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>
> > > > ---
> > >
> > > Another patch to fix the same thing was sent earlier as a follow up to the original series.
> > > https://marc.info/?l=linux-usb&m=151298133524873&w=2
> > >
> > > But your patch includes the Fixes line with the commit id, which is nice.
> > >
> > > Both fix the problem, It doesn't matter for me which one gets applied
> >
> > They fix it in different ways, which is correct?
>
> Both are correct, 'sizeof(dbc->eps)' is the same as 'sizeof(struct
> dbc_ep) * ARRAY_SIZE(dbc->eps)'.
>
> > And Arnd probably doesn't have the hardware to do so?
>
> Right.

Just to test and confirm boyh work I added a couple printk messages after memset()
showing bytes zeroed and method used:

# echo enabled > dbc
# cat dbc
enabled
# [  219.050277] xhci_hcd 0000:00:14.0: DbC connected
[  219.307250] xhci_hcd 0000:00:14.0: DbC configured
[  219.313601] xhci_hcd 0000:00:14.0: DbC now attached to /dev/ttyDBC0

# echo disabled > dbc
[  255.745590] xhci_hcd 0000:00:14.0: set 80 bytes to zero sizeof(struct dbc_ep) * ARRAY_SIZE(dbc->eps)
[  255.755970] xhci_hcd 0000:00:14.0: set 80 bytes to zero sizeof(dbc->eps)

-Mathias