Commit 55741c72 authored by Niklas Neronin's avatar Niklas Neronin Committed by Greg Kroah-Hartman
Browse files

usb: xhci: correct debug message page size calculation 



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: 81720ec5 ("usb: host: xhci: use ffs() in xhci_mem_init()")
Signed-off-by: default avatarNiklas Neronin <niklas.neronin@linux.intel.com>
Signed-off-by: default avatarMathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20250306144954.3507700-9-mathias.nyman@linux.intel.com


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent fe1ccba5

drivers/usb/host/xhci-mem.c

+3 −3
Original line number Diff line number Diff line
@@ -2391,10 +2391,10 @@ 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 */