Re: [RFC PATCH] USB: xhci: Enable HCE event reset function

[liulongfang <liulongfang@huawei.com>]

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@huawei.com>
>>>>> ---
>>>>>  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@intel.com> (supporter:USB XHCI DRIVER)
>>>> Greg Kroah-Hartman <gregkh@linuxfoundation.org> (supporter:USB SUBSYSTEM)
>>>> linux-usb@vger.kernel.org (open list:USB XHCI DRIVER)
>>>> linux-kernel@vger.kernel.org (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.
sysfs: a virtual file system based on memory, it's similar as proc.
Use DEVICE_ATTR or DRIVER_ATTR to create files to the /sys directory
Thanks
Longfang.