Hi,
Mathias Nyman <mathias.nyman@xxxxxxxxx> writes:
>>>> Get page size order using ffs() instead of open coding it with a loop.
>>>>
>>>> Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
>>>> Cc: Mathias Nyman <mathias.nyman@xxxxxxxxx>
>>>> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
>>>> Cc: linux-usb@xxxxxxxxxxxxxxx
>>>> Cc: linux-kernel@xxxxxxxxxxxxxxx
>>>> ---
>>>> drivers/usb/host/xhci-mem.c | 6 +-----
>>>> 1 file changed, 1 insertion(+), 5 deletions(-)
>>>>
>>>> diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
>>>> index 36a3eb8849f1..44b43c3d819f 100644
>>>> --- a/drivers/usb/host/xhci-mem.c
>>>> +++ b/drivers/usb/host/xhci-mem.c
>>>> @@ -2362,11 +2362,7 @@ int xhci_mem_init(struct xhci_hcd *xhci, gfp_t flags)
>>>> page_size = readl(&xhci->op_regs->page_size);
>>>> xhci_dbg_trace(xhci, trace_xhci_dbg_init,
>>>> "Supported page size register = 0x%x", page_size);
>>>> - for (i = 0; i < 16; i++) {
>>>> - if ((0x1 & page_size) != 0)
>>>> - break;
>>>> - page_size = page_size >> 1;
>>>> - }
>>>> + i = ffs(page_size);
>>>> if (i < 16)
>>>> xhci_dbg_trace(xhci, trace_xhci_dbg_init,
>>>> "Supported page size of %iK", (1 << (i+12)) / 1024);
>>>
>>> Hi
>>>
>>> using ffs() is a welcome change, but it will give different a result than the loop.
>>>
>>> *old loop
>>> valid page_size value if i < 16
>>> *ffs()
>>> valid page_size value if i >= 1 and i < 17
>>
>> off-by-one, just use i = ffs() - 1. Or use __ffs().
>
> and handle the page_size == 0 case.
Can it be zero in real life, or are you protecting against academic
possibility that's never going to happen in HW?
--
balbi
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