6.13-stable review patch. If anyone has any objections, please let me know.
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From: Niklas Neronin niklas.neronin@linux.intel.com
[ 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... Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/usb/host/xhci-mem.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/drivers/usb/host/xhci-mem.c b/drivers/usb/host/xhci-mem.c index fdf0c1008225a..9aa7e2a876ec1 100644 --- a/drivers/usb/host/xhci-mem.c +++ b/drivers/usb/host/xhci-mem.c @@ -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 */