Thanks Alan
On Fri, Jul 8, 2011 at 2:15 PM, Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Fri, 8 Jul 2011, Subodh Raiborde wrote:
>
>> Hi,
>>
>> I need to reduce the max power that can be drawn by any USB device to 250 mA.
>> I want to do this from the host end (linux).
>>
>> From what I understand the USB configuration is provided by the USB
>> device attached to the
>> host and the host reads the bMaxPower from it and if the bMaxPower
>> requested is below requested particular limit (say 500 mA)
>> then the device is allowed to receive the requested power. I want to
>> change that limit to 250mA so that no device can draw more than that.
>>
>> Please let me know the best way to do this.
>
> In drivers/usb/core/hub.c:hub_configure(), find these lines:
>
> if (hdev == hdev->bus->root_hub) {
> if (hdev->bus_mA == 0 || hdev->bus_mA >= 500)
> hub->mA_per_port = 500;
>
> ...
>
> } else { /* Self-powered external hub */
> /* FIXME: What about battery-powered external hubs that
> * provide less current per port? */
> hub->mA_per_port = 500;
> }
>
> and change the 500 values to 250.
>
> Alan Stern
>
>
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