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

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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: Marek Vasut <marex@denx.de>
Cc: Simon Glass <sjg@chromium.org>
This commit is contained in:
Marek Vasut 2013-12-13 23:36:33 +01:00
parent 3990994c43
commit 8fb83547b9
1 changed files with 25 additions and 3 deletions
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28
drivers/usb/host/ehci-pci.c
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@ -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,
&class);
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 (class != PCI_CLASS_SERIAL_USB_EHCI)
continue;
if (index) {
index--;
continue;
}
/* Return index'th controller. */
return bdf;
}
}
}