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

[Mathias Nyman]

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
 
-Mathias