usb: xhci: correct debug message page size calculation

[ Upstream commit 55741c723318905e6d5161bf1e12749020b161e3 ]

The ffs() function returns the index of the first set bit, starting from 1.
If no bits are set, it returns zero. This behavior causes an off-by-one
page size in the debug message, as the page size calculation [1]
is zero-based, while ffs() is one-based.

Fix this by subtracting one from the result of ffs(). Note that since
variable 'val' is unsigned, subtracting one from zero will result in the
maximum unsigned integer value. Consequently, the condition 'if (val < 16)'
will still function correctly.

[1], Page size: (2^(n+12)), where 'n' is the set page size bit.

Fixes: 81720ec5320c ("usb: host: xhci: use ffs() in xhci_mem_init()")
Signed-off-by: Niklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20250306144954.3507700-9-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c
index b0137eac7ab383c68540e1ee195d55769695b2dd..fbc486546b85338027acc58000a9200048b97c91 100644 (file)
--- a/drivers/usb/host/xhci-mem.c
+++ b/drivers/usb/host/xhci-mem.c
@@ -2318,10 +2318,10 @@ 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);
-       i = ffs(page_size);
-       if (i < 16)
+       val = ffs(page_size) - 1;
+       if (val < 16)
                xhci_dbg_trace(xhci, trace_xhci_dbg_init,
-                       "Supported page size of %iK", (1 << (i+12)) / 1024);
+                       "Supported page size of %iK", (1 << (val + 12)) / 1024);
        else
                xhci_warn(xhci, "WARN: no supported page size\n");
        /* Use 4K pages, since that's common and the minimum the HC supports */