From mboxrd@z Thu Jan 1 00:00:00 1970 From: Timur Mehrvarz Subject: Re: ehci-tegra issue with deep sleep Date: Mon, 07 Jan 2013 18:19:34 +0100 Message-ID: <50EB03A6.9040509@riseup.net> References: <50C7B250.7020409@riseup.net> <50C8C47A.1080809@wwwdotorg.org> <50E570F1.4030706@riseup.net> <50E71272.5090107@wwwdotorg.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <50E71272.5090107-3lzwWm7+Weoh9ZMKESR00Q@public.gmane.org> Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Stephen Warren Cc: linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-tegra@vger.kernel.org On 01/04/2013 06:33 PM, Stephen Warren wrote: > On 01/03/2013 04:52 AM, Timur wrote: > ... >> maybe you remember this brief conversation in December. I found the root >> cause of the reported issue (tegra specific) and I can provide a patch. >> The outcome is stable, externally powered USB host mode for Nexus 7. > Isn't USB host mode by definition internally powered, and USB device > mode by definition externally powered? An externally powered USB host > mode sounds quite non-standard. If you allow that mode, how does the > system know whether it should be a host or a device when external power > is applied; it sounds like this new mode completely breaks the ability > to connect the tablet to a PC and use it for Android application > development, or MTP (Media Transfer Protocol) to download pictures/movies. What I am proposing does not result in any loss of original functionality (ADB, MTP, etc.). Also, the described added functionality is fully standard when I look at it. No typical PC needs to switch to battery power, only to connect USB slave devices. You can operate a Nexus 7 on external power. But in order to connect USB slave devices, you *have* to switch to internal battery. Not being able to run USB host mode at all, while using external power, is a serious shortcoming. One that is only caused by the installed kernel. In December, I was having this last difficulty: preserving USB host operations through LP0 phases. But this problem has been solved. Really wanted to clarify this. > >> Do you happen to know anyone responsible for the Ubuntu Nexus7 kernel? I >> would like to contribute the fix, as I think it would be beneficial to >> that implementation. > Sorry, I don't know what kernel they're using; the best place to ask > would be the Ubuntu project itself. No, I did not ask what kernel they are using.