On Mon, 5 Mar 2007, Valentin Longchamp wrote: > Now I have a more precise question about the actual implementation of > Freescale i.MX31 kernel release (here is the patch: > http://bitshrine.org/gpp/linux-2.6.16-mx31-usb-2.patch). It works well, but > only with low-current devices (I have tested the ehci support with USB > pendrive flash disk). But when I try to plug in some higher current consumers > like a wifi pendrive for instance, which needs 300 mA, the configuration is > rejected because of this from the choose_configuration function in > drivers/usb/core/hub.c : > > > /* > > * The next test may not be as effective as it should be. > > * Some hubs have errors in their descriptor, claiming > > * to be self-powered when they are really bus-powered. > > * We will overestimate the amount of current such hubs > > * make available for each port. > > * > > * This is a fairly benign sort of failure. It won't > > * cause us to reject configurations that we should have > > * accepted. > > */ > > > > /* Rule out configs that draw too much bus current */ > > if (c->desc.bMaxPower * 2 > udev->bus_mA) > > continue; > > >From what I understand (I'm not very familiar with kernel USB code) > c->desc.bMaxPower is what the hub makes available for each port and > udev->bus_mA is what the device requests.
It's the reverse: (c->desc.bMaxPower * 2) is what the device requests and udev->bus_mA is what the hub makes available. > This has failed for me with a > device requesting 300 mA. > > Now I was not able to find in the code where this limit is fixed for my ehci > hardware. Because I haven't found a current limitation in the USB block or > transceiver (Phillips ISP1504) documentation (quick look). Search for "power_budget" in the source code for your bus glue. Alan Stern ------------------------------------------------------------------------- Take Surveys. Earn Cash. Influence the Future of IT Join SourceForge.net's Techsay panel and you'll get the chance to share your opinions on IT & business topics through brief surveys-and earn cash http://www.techsay.com/default.php?page=join.php&p=sourceforge&CID=DEVDEV _______________________________________________ linux-usb-devel@lists.sourceforge.net To unsubscribe, use the last form field at: https://lists.sourceforge.net/lists/listinfo/linux-usb-devel
