Hi Benhard,
On 22 June 2016 at 03:05, Bernhard Nortmann <bernhard.nortm...@web.de> wrote:
> Starting with commit b19236fd1c1ef289bab9e243ee5b50d658fcac3f I am observing
> a breakage of the "usb info" command on my BananaPi (Allwinner A20, sun7i),
> while "usb tree" and dm commands ("dm tree", "dm uclass") are fine.
> See attached usb-info-breakage.log
>
> Tracing back the error positon from pc and lr registers pointed me to the
> device_get_uclass_id() call within usb_device_info(), and suggested the
> problem is caused by trying to dereference a NULL struct udevice *hub.
>
> Therefore I added a diagnostic printf and a safeguard to this routine:
>
> diff --git a/cmd/usb.c b/cmd/usb.c
> index b83d323..a5e2463 100644
> --- a/cmd/usb.c
> +++ b/cmd/usb.c
> @@ -610,6 +610,12 @@ static int usb_device_info(void)
> struct udevice *hub;
>
> device_find_first_child(bus, &hub);
> + printf("bus %p, uclass %d, hub %p: ",
> + bus, device_get_uclass_id(bus), hub);
> + if (!hub) {
> + printf("<no hub>\n");
> + continue;
> + }
> if (device_get_uclass_id(hub) == UCLASS_USB_HUB &&
> device_active(hub)) {
> show_info(hub);
>
> And it became apparent that hub actually receives NULL values during the
> device enumeration. The safeguard prevented the "data abort" error and got
> "usb info" working again - see attached usb-info-fixed.log
>
> I'm not sure why this particular problem didn't manifest earlier and
> only now became apparent with the change in SPL header size /
> CONFIG_SPL_TEXT_BASE. But it seems that accessing a NULL hub with
> device_get_uclass_id() is clearly wrong and should be avoided.
> Which brings me to two questions:
>
> 1. Is getting a NULL hub value legit when iterating UCLASS_USB devices
> the way that usb_device_info() does? If yes, the code seems to be
> lacking protection against passing it to device_get_uclass_id().
Well if there are no child devices of a USB controller, then yes.
Normally there is at least one (a USB hub). But this code is wrong -
it should not assume that.
In fact. now, the new uclass_first_device_err() function is probably a
better choice, since it returns an error if nothing is found.
>
> 2. Why does usb_device_info() choose to enumerate hubs this way at all?
> If the routine is aiming at UCLASS_USB_HUB - which seems to be the
> purpose of the subsequent device_get_uclass_id(hub) test - and the
> device tree already provides this information (as suggested by the
> output of "dm uclass"), then why not enumerate UCLASS_USB_HUB directly?
It was probably trying to duplicate the operation of the old code:
if (strncmp(argv[1], "inf", 3) == 0) {
if (argc == 2) {
#ifdef CONFIG_DM_USB
usb_device_info();
#else
int d;
for (d = 0; d < USB_MAX_DEVICE; d++) {
udev = usb_get_dev_index(d);
if (udev == NULL)
break;
usb_display_desc(udev);
usb_display_config(udev);
}
#endif
But I'm not sure that the ordering would change in any case, or even
if it matters. Feel free to change it to enumerate USB_HUB.
Another explanation is that originally I was not sure if USB hubs
should have their own uclass. With PCI bridges we don't do it that
way. But I decided in the end to go ahead, and I think it has worked
ouit. So perhaps the code was converted mid-stream.
>
> Regards, B. Nortmann
>
Regards,
Simon
_______________________________________________
U-Boot mailing list
U-Boot@lists.denx.de
http://lists.denx.de/mailman/listinfo/u-boot
