On Tue, Aug 20, 2024, Zhongqiu Han wrote: > Busy loops that poll on a register should call cpu_relax(). On some > architectures, it can lower CPU power consumption or yield to a > hyperthreaded twin processor. It also serves as a compiler barrier, > see Documentation/process/volatile-considered-harmful.rst. 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/dwc3/core.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/drivers/usb/dwc3/core.c b/drivers/usb/dwc3/core.c > index 734de2a8bd21..498f08dbbdb5 100644 > --- a/drivers/usb/dwc3/core.c > +++ b/drivers/usb/dwc3/core.c > @@ -2050,6 +2050,8 @@ static int dwc3_get_num_ports(struct dwc3 *dwc) > if (!offset) > break; > > + cpu_relax(); > + > val = readl(base + offset); > major_revision = XHCI_EXT_PORT_MAJOR(val); > > -- > 2.25.1 > We're not polling on a register here. We're just traversing and reading the next port capability. The loop in dwc3_get_num_ports() should not be more than DWC3_USB2_MAX_PORTS + DWC3_USB3_MAX_PORTS. What's really causing this busy loop you found? If polling for a register is really a problem, then we would have that problem everywhere else in dwc3. But why here? Thanks, Thinh
