Commit 8fb83547 authored by Marek Vasut's avatar Marek Vasut
Browse files

usb: ehci-pci: Clarify and cleanup the EHCI controller detection

The detection function of the EHCI PCI controller was really cryptic,
add a beefy comment and clean the portion of the code up a bit. No
change in the logic of the code.
Signed-off-by: default avatarMarek Vasut <>
Cc: Simon Glass <>
parent 3990994c
......@@ -54,9 +54,31 @@ static pci_dev_t ehci_find_class(int index)
bdf += PCI_BDF(0, 0, 1)) {
pci_read_config_dword(bdf, PCI_CLASS_REVISION,
if ((class >> 8 == PCI_CLASS_SERIAL_USB_EHCI)
&& !index--)
return bdf;
class >>= 8;
* Here be dragons! In case we have multiple
* PCI EHCI controllers, this function will
* be called multiple times as well. This
* function will scan the PCI busses, always
* starting from bus 0, device 0, function 0,
* until it finds an USB controller. The USB
* stack gives us an 'index' of a controller
* that is currently being registered, which
* is a number, starting from 0 and growing
* in ascending order as controllers are added.
* To avoid probing the same controller in tne
* subsequent runs of this function, we will
* skip 'index - 1' detected controllers and
* report the index'th controller.
if (index) {
/* Return index'th controller. */
return bdf;
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