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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