Re: [PATCH 2/2] usb: xhci: ext-caps: Use cpu_relax() when polling registers

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On 8/21/2024 5:40 PM, Mathias Nyman wrote:
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

Hi Mathias,
Thanks a lot for the review, yes, it is similar case as with PATCH 1/2
there is not a busy loop polling, sorry for this and i will careful for
similar case next time, and thanks for the discussion as well.

--
Thx and BRs,
Zhongqiu Han




[Index of Archives]     [Linux Media]     [Linux Input]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Old Linux USB Devel Archive]

  Powered by Linux