Re: [PATCH] xhci: Use ffs() to find page size in xhci_mem_init()

[Felipe Balbi]

Hi,

Mathias Nyman <mathias.ny...@linux.intel.com> writes:
> On 07.02.2019 02:03, Andrey Smirnov wrote:
>> Get page size order using ffs() instead of open coding it with a loop.
>> 
>> Signed-off-by: Andrey Smirnov <andrew.smir...@gmail.com>
>> Cc: Mathias Nyman <mathias.ny...@intel.com>
>> Cc: Greg Kroah-Hartman <gre...@linuxfoundation.org>
>> Cc: linux-...@vger.kernel.org
>> Cc: linux-kernel@vger.kernel.org
>> ---
>>   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().

-- 
balbi

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