linux-kernel - Why USB Link Power Management only for devices connected to root hub

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Date:	Tue, 22 May 2012 11:42:28 +0530
From:	prasannatsmkumar <prasannatsmkumar@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Why USB Link Power Management only for devices connected to root hub

I have started looking into USB stuff. In the EHCI driver code I could
see the comment that "we only support lpm device connected to root hub
yet" in drivers/usb/host/ehci-pci.c line 466 (3.4 kernel -
http://lxr.free-electrons.com/source/drivers/usb/host/ehci-pci.c#L466).
Is there any reason to not support lpm in devices connected to hub
(other than root hub)? Also inside ehci_lpm_check function in
drivers/usb/host/ehci-lpm.c (3.4 kernel -
http://lxr.free-electrons.com/source/drivers/usb/host/ehci-lpm.c) the
USB device is asked to go to LPM mode and there is a wait for 10ms. I
guess the LPM transition (L0 to L1 state transition) should take place
within some micro seconds then why should we wait for 10ms for ACK?

Thanks,
Prasanna Kumar T S M
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/