On Thu, Nov 19, 2020 at 09:50:20AM +0800, liulongfang wrote:
> On 2020/11/19 0:21, Mathias Nyman Wrote:
> > On 18.11.2020 11.14, Greg KH wrote:
> >> On Wed, Nov 18, 2020 at 05:04:36PM +0800, liulongfang wrote:
> >>> On 2020/11/18 15:02, Greg KH Wrote:
> >>>> On Wed, Nov 18, 2020 at 11:36:13AM +0800, Longfang Liu wrote:
> >>>>> The HCE(Host Controller Error) event has been defined in
> >>>>> the XHCI driver but has not been used. If we want to use
> >>>>> the HCE event to reset the controller, can we implement
> >>>>> it in the interrupt function as follows:
> >>>>>
> >>>>> xhci_irq()
> >>>>> |----xhci_halt()
> >>>>> |----xhci_shutdown()
> >>>>> |----xhci_start()
> >>>>> |----xhci_run()
> >>>>>
> >>>>> Signed-off-by: Longfang Liu <liulongfang@xxxxxxxxxx>
> >>>>> ---
> >>>>> drivers/usb/host/xhci-ring.c | 10 ++++++++++
> >>>>> 1 file changed, 10 insertions(+)
> >>>>
> >>>> $ ./scripts/get_maintainer.pl --file drivers/usb/host/xhci-ring.c
> >>>> Mathias Nyman <mathias.nyman@xxxxxxxxx> (supporter:USB XHCI DRIVER)
> >>>> Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> (supporter:USB SUBSYSTEM)
> >>>> linux-usb@xxxxxxxxxxxxxxx (open list:USB XHCI DRIVER)
> >>>> linux-kernel@xxxxxxxxxxxxxxx (open list)
> >>>>
> >>>> Any reason to not include the maintainer of the xhci driver here?
> >>> OK, I will include the maintainer in the next patch.
> >>>>
> >>>>> diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
> >>>>> index 2c255d0..87b3a40 100644
> >>>>> --- a/drivers/usb/host/xhci-ring.c
> >>>>> +++ b/drivers/usb/host/xhci-ring.c
> >>>>> @@ -2857,6 +2857,16 @@ irqreturn_t xhci_irq(struct usb_hcd *hcd)
> >>>>> goto out;
> >>>>> }
> >>>>>
> >>>>> + if (status & STS_HCE) {
> >>>>> + xhci_warn(xhci, "WARNING: Host Controller Error\n");
> >>>>> + xhci_halt(xhci);
> >>>>> + xhci_shutdown(hcd);
> >>>>> + xhci_start(xhci);
> >>>>> + xhci_run(hcd);
> >>>>> + ret = IRQ_HANDLED;
> >>>>> + goto out;
> >>>>> + }
> > This won't work at all. It doesn't reset the xHC which is the one thing needed to
> > recover from a HCE. This would deadlock immediately.
> > Many of the above functions shouldn't be called from interrupt context, and if
> > HCE is set we probably even won't get any interrupts.
> >
> > A reset will set all registers to their initial values, and need to be
> > re-initialized. Nothing is freed or re-allocated, registrs are not re-initialized
> > here.
> >
> > Please revisit the xhci spec about HCE, and HCRST, and a more detail look
> > at the xhci driver, and test the code before submitting.
> >
> >>>>> +
> >>>>
> >>>> Does this fix a real problem for you? Are you sure we will not suddenly
> >>>> start resetting devices that were working properly and sending this
> >>>> error incorrectly? How did you test this?
> >>>>
> >>>> thanks,
> >>>>
> >>>> greg k-h
> >>>> .
> >>>>
> >>> Yes, we want to add a RAS feature to the USB,
> >>
> >> What is "RAS"?
> >>
> >>> Use the HCE event to trigger the reset operation of the USB controller.
> >>
> >> Is that allowed by the XHCI specification?
> >>
> >>> By searching for the current xhci driver, the driver did not handle HCE event.
> >>> In fact, I am not sure if other operations will cause HCE, The HCE event is
> >>> used to reset the USB controller according to the definition of the event.
> >>
> >> What generates that event? Do existing controllers do that today? What
> >> causes it?
> >>
> >
> > It's not an event, it's a controller internal error state.
> > It's probably not very useful to check for it in the interrupt handler as
> > the xHC hw ceases all activity when it sets the HCE bit, including sending
> > interrupts.
> >
> >>>From the spec:
> >
> > 4.24.1 Internal Errors
> > The Host Controller Error (HCE) flag is asserted when an internal xHC error is
> > detected that exclusively affects the xHC. When the HCE flag is set to ‘1’ the xHC
> > shall cease all activity. Software response to the assertion of HCE is to reset the
> > xHC (HCRST = ‘1’) and reinitialize it
> >
> >>> I test this reset operation through the Sysfs file, but have not tested all usage scenarios.
> >>
> >> What sysfs file?
> >
> > I'm also interested in this, and to know more about RAS?
> >
> > Thanks
> > -Mathias
> > .
> >
> RAS: Reliablity, Availability and Serviceability.
That's a marketing phrase, what specifically are you talking about when
it comes to the xhci driver?
> sysfs: a virtual file system based on memory, it's similar as proc.
I am very aware of what sysfs is, look at the MAINTAINERS entry for it :)
> Use DEVICE_ATTR or DRIVER_ATTR to create files to the /sys directory
Yes, but what file did you use for this? I don't see one in the kernel
that can cause this, do you?
thanks,
greg k-h
