Re: [PATCH 4/5] usb: ehci-hcd: use mdelay_non_inerruptible()

[Peter Mamonov <pmamonov@gmail.com>]

On Mon, 12 Oct 2015 09:00:21 +0200
Sascha Hauer <s.hauer@pengutronix.de> wrote:

> On Wed, Oct 07, 2015 at 07:52:21PM +0300, Peter Mamonov wrote:
> > On Wed, 7 Oct 2015 17:40:24 +0200
> > > > Non-interruptible delays are needed here to prevent ehci_*
> > > > functions re-entrance. The re-entrance occurs during a usb bus
> > > > scan, after detection of a usb keyboard. As soon as a USB
> > > > keyboard is detected, it's driver starts the poller, which
> > > > interferes with the process of usb bus scan. However that last
> > > > one delay may be interruptible.
> > > 
> > > my problem is as soon as you start a usb control msg you block
> > > everything
> > > 
> > > nothing else can run in barebox
> > > 
> > > can slow down barebox boot
> > > 
> > > I do think we need a real mdelay_non_interruptible feature but
> > > just forbidden to recall usb control msg.
> > > But the rest of barebox can run durring those 5ms
> > 
> > Well, I think it can be done by returning -EAGAIN on re-entrance
> > detection in ehci_* functions [1], and skipping the poll in the
> > keyboard driver.
> 
> Could you tell us what you have done to get re-entrance problems? I
> have just replaced the mdelay_non_interruptible with regular mdelay
> in the ehci driver and didn't notice any problems. Could you verify
> the _non_interruptible is still needed?

If I revert the "usb: ehci-hcd: use mdelay_non_interruptible()" patch,
while leaving the "usb: ehci-hcd: detect re-entrance" applied, I get
the following messages after running the "usb" command:

barebox:/ usb                                                         
USB: scanning bus for devices...                                                
Bus 001 Device 001: ID 0000:0000 EHCI Host Controller                           
Bus 001 Device 002: ID 0424:2514                                                
Bus 001 Device 003: ID 413c:2112 Dell USB Wired Multimedia Keybo                
usb-keyboard usb1-0-0: USB keyboard found                                       
Bus 001 Device 004: ID 8564:1000 Mass Storage Device                            
Using index 0 for the new disk                                                  
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-hub:usb1)             
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-hub:usb1)             
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-keyboard:usb1-0-0)    
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-keyboard:usb1-0-0)    
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-hub:usb1)             
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-keyboard:usb1-0-0)    
usb-keyboard usb1-0-0: submit_int_msg: re-entrance 1 (usb-keyboard:usb1-0-0)    
Bus 001 Device 005: ID 0424:2514                                                
5 USB Device(s) found                                                       

According to the debug messages: submit_int_msg() is called by the usb-keyboard driver (from the poller function),
while "usb-hub" driver is executing submit_control_msg() (which calls mdelay() and poller_call() subsequently).
This occurs several times, until usb bus scan is completed.
Probably the problem can be reproduced by adding more usb devices.

> 
> Sascha
> 


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