Re: [PATCH V5 8/8] usb : Add usb port's power control attributes

[Lan Tianyu <tianyu.lan@xxxxxxxxx>]

On 2012年06月30日 23:22, Alan Stern wrote:
> On Sat, 30 Jun 2012, Lan Tianyu wrote:
>
> > > > Do you mean while a new device was enumerating, the port powered off? I
> > > > guess the enumerating process will fail.
> > >
> > > That's what I thought too, but I haven't actually tried it.  Something
> > > strange might happen when two different threads send concurrent
> > > messages to the same hub port.  You might want to do a few experiments.
> > Ok. I will do some experiments. But I guess it may be hard. Those two
> > operation maybe too quirk to be simultaneous. :)
>
> Add ssleep() calls at the right spots.  Then you can make anything
> happen the way you want.  :-)
>
> > What's concurrent messages? I think even from the two threads, messages
> > will also be processed in the message queue in order. Right?
>
> Yes, they will be.  But even so, messages from one thread might occur
> in between messages from a different thread.
hi alan:
	I have done some experiments. I insert clear PORT_POWER in the 
hub_port_connect_change()
to simulate such situation. I found there is leak if I clear PORT_POWER in the 
hub_port_connect_change()
after hub_port_init() and before usb_new_device().

[    7.083502] xhci_hub_control: clear port power, actual port 1 status  = 0xe01
[    7.090793] usb 1-2: unable to read config index 0 descriptor/start: -71
[    7.097469] usb 1-2: chopping to 0 config(s)
[    7.098898] ata2: SATA link up 1.5 Gbps (SStatus 113 SControl 300)
[    7.107898] ata2.00: ATAPI: Optiarc BD ROM BC-5640H, 1.00, max UDMA/100
[    7.107982] usb 1-2: string descriptor 0 read error: -71
[    7.107988] usb 1-2: New USB device found, idVendor=0781, idProduct=5567
[    7.107990] usb 1-2: New USB device strings: Mfr=1, Product=2, SerialNumber=3
[    7.108144] usb 1-2: no configuration chosen from 0 choices
In usb_get_configuration(),  usb_get_descriptor failed but not return err. The 
device
was still enumerated. I do following change and it works. Why here don't return err?

diff --git a/drivers/usb/core/config.c b/drivers/usb/core/config.c
index f4bdd0c..90f962b 100644
--- a/drivers/usb/core/config.c
+++ b/drivers/usb/core/config.c
@@ -704,7 +704,7 @@ int usb_get_configuration(struct usb_device *dev)
                            "descriptor/%s: %d\n", cfgno, "start", result);
                        dev_err(ddev, "chopping to %d config(s)\n", cfgno);
                        dev->descriptor.bNumConfigurations = cfgno;
-                       break;
+                       goto err;
                } else if (result < 4) {
                        dev_err(ddev, "config index %d descriptor too short "
                            "(expected %i, got %i)\n", cfgno,

> Alan Stern

--
Best Regards
Tianyu Lan
linux kernel enabling team
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