On Tue, 11 Feb 2020, Dan Carpenter wrote:
> Hello USB devs,
>
> The patch 7d50195f6c50: "usb: host: Faraday fotg210-hcd driver" from
> Jul 29, 2013, leads to the following static checker warning:
>
> drivers/usb/host/fotg210-hcd.c:3945 iso_stream_init()
> warn: mask and shift to zero
>
> drivers/usb/host/fotg210-hcd.c
> 3922 static void iso_stream_init(struct fotg210_hcd *fotg210,
> 3923 struct fotg210_iso_stream *stream, struct usb_device *dev,
> 3924 int pipe, unsigned interval)
> 3925 {
> 3926 u32 buf1;
> 3927 unsigned epnum, maxp;
> 3928 int is_input;
> 3929 long bandwidth;
> 3930 unsigned multi;
> 3931
> 3932 /*
> 3933 * this might be a "high bandwidth" highspeed endpoint,
> 3934 * as encoded in the ep descriptor's wMaxPacket field
> 3935 */
> 3936 epnum = usb_pipeendpoint(pipe);
> 3937 is_input = usb_pipein(pipe) ? USB_DIR_IN : 0;
> 3938 maxp = usb_maxpacket(dev, pipe, !is_input);
> 3939 if (is_input)
> 3940 buf1 = (1 << 11);
> 3941 else
> 3942 buf1 = 0;
> 3943
> 3944 maxp = max_packet(maxp);
> 3945 multi = hb_mult(maxp);
> 3946 buf1 |= maxp;
> 3947 maxp *= multi;
This is pretty clearly a case of mistaken reuse of a local variable.
The argument to hb_mult() should be the output from usb_maxpacket(),
not the result of the max_packet() calculation.
> 3948
> 3949 stream->buf0 = cpu_to_hc32(fotg210, (epnum << 8) | dev->devnum);
> 3950 stream->buf1 = cpu_to_hc32(fotg210, buf1);
> 3951 stream->buf2 = cpu_to_hc32(fotg210, multi);
>
> The problem is these two defines:
>
> #define max_packet(wMaxPacketSize) ((wMaxPacketSize) & 0x07ff)
> #define hb_mult(wMaxPacketSize) (1 + (((wMaxPacketSize) >> 11) & 0x03))
>
> 0x07ff >> 11 is always zero so multi is always 1.
>
> Should we pass the original value that usb_maxpacket() returned instead
> of the masked value?
Yes. I suggest introducing a new local variable and using it in place
of maxp in lines 3938, 3944 (the second occurrence), and 3945.
Alan Stern
> regards,
> dan carpenter
