Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755990Ab3HLJwS (ORCPT ); Mon, 12 Aug 2013 05:52:18 -0400 Received: from cassiel.sirena.org.uk ([80.68.93.111]:36364 "EHLO cassiel.sirena.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755382Ab3HLJwQ (ORCPT ); Mon, 12 Aug 2013 05:52:16 -0400 Date: Mon, 12 Aug 2013 10:51:36 +0100 From: Mark Brown To: Alan Stern Cc: Rob Herring , Pawel Moll , Mark Rutland , Stephen Warren , Ian Campbell , Felipe Balbi , Greg Kroah-Hartman , Grant Likely , devicetree@kernel.org, linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: <20130812095136.GJ6427@sirena.org.uk> References: <20130811190826.GH6427@sirena.org.uk> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="7OnDFbl3rdzPmmvv" Content-Disposition: inline In-Reply-To: X-Cookie: Many pages make a thick book. User-Agent: Mutt/1.5.21 (2010-09-15) X-SA-Exim-Connect-IP: 94.175.92.69 X-SA-Exim-Mail-From: broonie@sirena.org.uk Subject: Re: Non-enumerable devices on USB and other enumerable buses X-SA-Exim-Version: 4.2.1 (built Mon, 26 Dec 2011 16:57:07 +0000) X-SA-Exim-Scanned: Yes (on cassiel.sirena.org.uk) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3172 Lines: 69 --7OnDFbl3rdzPmmvv Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sun, Aug 11, 2013 at 09:53:01PM -0400, Alan Stern wrote: > On Sun, 11 Aug 2013, Mark Brown wrote: > > One example that's bugging me right now is that on the Insignal Arndale > > platform there's a USB hub connected to one of the USB ports on the SoC > > (not as a PHY, it seems we also need the internal PHY running to talk to > > the device). The hub needs to be "plugged" into the SoC after the SoC > > USB controller has started with some GPIOs so we need to tell the system > > that the hub exists and needs to be synchronised with the USB controlle= r. > On the surface, this seems like a particularly simple case. Why wait=20 > until the SoC's USB controller has started? Why not "plug in" the hub=20 > via the GPIOs right from the beginning? I tried that, it doesn't seem to work - for some reason it seems that the hub is only successfully enumerated if it starts after its parent is running. I don't know enough about USB to speculate on why that might be, the GPIOs are brining the device out of reset not applying power or anything. > > Another case that's going to be problematic once it's in mainline is > > Slimbus - this is a bus used in some embedded audio subsystems which is > > enumerable in a similar manner to USB but where the devices on the bus > > are normally powered up only on demand (causing them to hotplug when > > used and unplug when idle) and have at least interrupt lines wired to > > the SoC using a normal interrupt outside the enumerable bus. > That is indeed more difficult, because it requires geniune cooperation=20 > between the bus and platform subsystems. Yeah. You might want to do the same with for example a USB network controller when you're in flight only mode, that seems to be one of the more common reasons for doing this sort of thing with USB. --7OnDFbl3rdzPmmvv Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.20 (GNU/Linux) iQIcBAEBAgAGBQJSCLAlAAoJELSic+t+oim98swP/j2DDHFTNziNJJHLm1xJ3tGw dsoRp0otZu/OHiRjT+GxoDITbmbU8Cc6V1OeBXijxVkL9FdOtr/n2zV4+dSfXXTn T/7me1OQvy2x3ypFnFhWswAeB30bsTDqWu3d4BbqhMvXuf0J+tElem7g2QceJ2zf cVChwLf8CNOV13RsSB/mjZk6XbJQpbcyF4PxXwsbbjw2KYnOu379QuoIGW9SmRvr WOu0kOVHWy6Yn78NUHgcnH+/D5ODLmFnz+O34A4KpGBuWDdmxHrRLuqiS5I4IIOF xqxjlYA9VpKUBLdL4z9O9f+WmrVColJjK3OGHGreWklbu8+X4i1tzw591p8F1GSD yyr57aCPQilRjbY5ygUcb4vcWtxTslI6/tLh9A13tG9V8SS6WYQR2tlBhCSRSN3C FRYCun4gPJYnmejhDubKUlPP4CrW2bMm+2ROLymiLu8q+vuvNtckkDnwgFpnHdF1 0q2WaM6tLLjRlIpLgE1l3iLFSqBq/0zCs1mAmdd8UQsSOR/Cywq9iwiLU2P4LThy 3+5sCYuCo3ItB52sGEOQtB4CBW1ryiHZjJQzt6Ic9Fm73T+yVTAqwISL0Ma/MWCV J3jZ3eyLEJ0bdtYqRfRV/YLH+Z/p0GL6aorUQ82PNGi0xXg3bNqU0W1T8rSvtfzu DXYow1KP5l8k8sdXeOBe =x0hs -----END PGP SIGNATURE----- --7OnDFbl3rdzPmmvv-- -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/