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SubjectRe: [PATCH 5/6] usb-hcd,usb-console: poll hcd device to force usb console writes
Alan Stern wrote:
> On Tue, 9 Mar 2010, Jason Wessel wrote:
>> This patch tries to solve the problem that data is lost because there
>> are too many outstanding transmit urb's while trying to execute
>> printk's to a console. The same is true if you try something like
>> "echo t > /proc/sysrq-trigger".
>> This patch takes the route of forcibly polling the hcd device to drain
>> the urb queue in order to initiate the bulk write call backs. This
>> only happens if the device is a usb serial console device that sets
>> the max_in_flight_urbs to a non zero value in the serial device
>> structure.
>> A few millisecond penalty will get incurred to allow the hcd controller
>> to complete a write urb, else the console data is thrown away.
>> The max_in_flight_urbs was reduced in the usb_debug driver because it
>> is highly desired to push things out to the console in a timely
>> fashion and there is no need to have a queue that large for the
>> interrupt driven mode of operation when used through the tty
>> interface.
>> --- a/drivers/usb/core/hcd.c
>> +++ b/drivers/usb/core/hcd.c
>> @@ -1973,6 +1973,7 @@ irqreturn_t usb_hcd_irq (int irq, void *__hcd)
>> local_irq_restore(flags);
>> return rc;
>> }
>> +EXPORT_SYMBOL_GPL(usb_hcd_irq);
> Is there any reason for EXPORTing this? It doesn't get used anywhere
> else.

Certainly not anymore. The previous iteration of this code used this
function. Thanks for catching that.

>> index a3cdb09..703f407 100644
>> --- a/drivers/usb/core/hcd.h
>> +++ b/drivers/usb/core/hcd.h
>> @@ -318,6 +318,7 @@ extern void usb_put_hcd(struct usb_hcd *hcd);
>> extern int usb_add_hcd(struct usb_hcd *hcd,
>> unsigned int irqnum, unsigned long irqflags);
>> extern void usb_remove_hcd(struct usb_hcd *hcd);
>> +extern void usb_hcd_poll_irq(struct usb_device *udev);
>> struct platform_device;
>> extern void usb_hcd_platform_shutdown(struct platform_device *dev);
> It might be better to put this in a "public" header file; that is,
> something under include/linux/usb or include/linux/usb.h. You could
> even take the "_hcd" part out of the name, because the interface uses
> only a struct usb_device, not a struct usb_hcd.

If this is what you prefer, I have no problem with it. I'll post a v2
of the series after some testing.


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