Hello Alan,
thanks for the reply.
On Mon, Jan 10, 2011 at 9:00 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Mon, 10 Jan 2011, Pratyush Anand wrote:
>
>> Hi All,
>>
>> As per USB 2.0 specification(Section 11.12.5 Over-current Reporting
>> and Recovery):
>>
>> When a hub experiences an over-current condition, it must place all
>> affected ports in the Powered-off state.
>>
>> It does not specify whether this action is to be done by hardware or software.
>
> Yes it does. It says "When a hub ... it must place ..." The word "it"
> refers back to the word "hub". This means that the hub must place all
> affected ports in the Powered-off state. In others words, the action
> is to be done by hardware.
>
OK.
>> I am working with controller where it expects port power off to be
>> done by software in case of overcurrent detection interrupt.
>
> Root hubs are different from external hubs. It is reasonable to expect
> software to turn off port power for root hubs.
>
The code which I had referred was from linux (except hub_power_off part).
linux+v2.6.37/drivers/usb/core/hub.c
line no: 3416
3416 if (hubchange & HUB_CHANGE_OVERCURRENT) {
3417 dev_dbg (hub_dev, "overcurrent change\n");
3418 msleep(500); /* Cool down */
3419 clear_hub_feature(hdev, C_HUB_OVER_CURRENT);
3420 hub_power_on(hub, true);
3421 }
3422 }
But, It does not turn off port power for root hubs.
Regards
Pratyush
>> So , implementation would be something like:
>>
>> if (hubchange & HUB_CHANGE_OVERCURRENT) {
>> dev_dbg (hub_dev, "overcurrent change\n");
>>
>> hub_power_off(hub);
>> msleep(500); /* Cool down */
>> clear_hub_feature(hdev, C_HUB_OVER_CURRENT);
>> hub_power_on(hub, true);
>> }
>>
>> Is this implementation correct?
>
> Not really. The spec also states: "Host waits for over-current status
> bit to be cleared to 0". Your code always waits for 500 ms, which
> could be either too long or too short. On the other hand, you mustn't
> wait indefinitely.
>
> Also, you have to do more or less the same thing when any ports report
> over-current status. In this case you would have to first turn off the
> power to all the affected ports, then wait, then turn on power to all
> of them.
>
> Alan Stern
>
>
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
