On 20.8.2024 15.15, Zhongqiu Han wrote:
It is considered good practice to call cpu_relax() in busy loops, see
Documentation/process/volatile-considered-harmful.rst. This can lower
CPU power consumption or yield to a hyperthreaded twin processor and
also serve as a compiler barrier. In addition, if something goes wrong
in the busy loop at least it can prevent things from getting worse.
Signed-off-by: Zhongqiu Han <quic_zhonhan@xxxxxxxxxxx>
---
drivers/usb/host/xhci-ext-caps.h | 2 ++
1 file changed, 2 insertions(+)
diff --git a/drivers/usb/host/xhci-ext-caps.h b/drivers/usb/host/xhci-ext-caps.h
index 96eb36a58738..25d148d60ab0 100644
--- a/drivers/usb/host/xhci-ext-caps.h
+++ b/drivers/usb/host/xhci-ext-caps.h
@@ -144,6 +144,8 @@ static inline int xhci_find_next_ext_cap(void __iomem *base, u32 start, int id)
if (offset != start && (id == 0 || XHCI_EXT_CAPS_ID(val) == id))
return offset;
+ cpu_relax();
+
next = XHCI_EXT_CAPS_NEXT(val);
offset += next << 2;
} while (next);
Similar case as with PATCH 1/2
This isn't a busy loop polling for some value.
We traverse xhci extended capabilities until the one we are looking for is found.
Thanks
Mathias
