From mboxrd@z Thu Jan 1 00:00:00 1970 From: Felipe Balbi Subject: Re: [PATCH v11 08/14] usb: otg: add OTG/dual-role core Date: Tue, 21 Jun 2016 11:18:21 +0300 Message-ID: <87mvmfneeq.fsf@linux.intel.com> References: <1465564043-27163-1-git-send-email-rogerq@ti.com> <1465564043-27163-9-git-send-email-rogerq@ti.com> <575E672E.5070603@ti.com> <87h9coxq04.fsf@linux.intel.com> <5767C1B9.2060805@ti.com> <878ty0qd7q.fsf@linux.intel.com> <20160621063936.GB5108@shlinux2> <87d1nbovp7.fsf@linux.intel.com> <20160621080209.GC5108@shlinux2> Mime-Version: 1.0 Content-Type: multipart/signed; boundary="=-=-="; micalg=pgp-sha256; protocol="application/pgp-signature" Return-path: In-Reply-To: <20160621080209.GC5108@shlinux2> Sender: devicetree-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Peter Chen Cc: Roger Quadros , peter.chen-KZfg59tc24xl57MIdRCFDg@public.gmane.org, yoshihiro.shimoda.uh-zM6kxYcvzFBBDgjK7y7TUQ@public.gmane.org, tony-4v6yS6AI5VpBDgjK7y7TUQ@public.gmane.org, gregkh-hQyY1W1yCW8ekmWlsbkhG0B+6BGkLq7r@public.gmane.org, dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, mathias.nyman-VuQAYsv1563Yd54FQh9/CA@public.gmane.org, Joao.Pinto-HKixBCOQz3hWk0Htik3J/w@public.gmane.org, sergei.shtylyov-M4DtvfQ/ZS1MRgGoP+s0PdBPR1lH4CV8@public.gmane.org, jun.li-KZfg59tc24xl57MIdRCFDg@public.gmane.org, grygorii.strashko-l0cyMroinI0@public.gmane.org, robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, nsekhar-l0cyMroinI0@public.gmane.org, b-liu-l0cyMroinI0@public.gmane.org, joe-6d6DIl74uiNBDgjK7y7TUQ@public.gmane.org, linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: devicetree@vger.kernel.org --=-=-= Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Hi, Peter Chen writes: >> Peter Chen writes: >> >> >>> + >> >> >>> + /* start host */ >> >> >>> + ret =3D hcd_ops->add(otg->primary_hcd.hcd, >> >> >>> + otg->primary_hcd.irqnum, >> >> >>> + otg->primary_hcd.irqflags); >> >> >>=20 >> >> >> this is usb_add_hcd(), is it not? Why add an indirection? >> >> > >> >> > I've introduced the host and gadget ops interface to get around the >> >> > circular dependency issue we can't avoid. >> >> > otg needs to call host/gadget functions and host/gadget also needs = to >> >> > call otg functions. >> >>=20 >> >> IMO, this shows a fragility of your design. You're, now, lying to >> >> usb_hcd and usb_udc and making them register into a virtual layer that >> >> doesn't exist. And that layer will end up calling the real registrati= on >> >> function when some magic event happens. >> >>=20 >> >> This is only really needed for quirky devices like dwc3 (but see more= on >> >> dwc3 below) where host and peripheral registers shadow each >> >> other. Otherwise we would be able to always keep hcd and udc always >> >> registered. They would get different interrupt statuses anyway and >> >> nothing would ever break. >> >>=20 >> >> However, when it comes to dwc3, we already have all the code necessary >> >> to workaround this issue by destroying the XHCI pdev when OTG interru= pt >> >> says we should be peripheral (and vice-versa). DWC3 also keeps track = of >> >> the OTG states for those folks who really care about OTG (Hint: nobody >> >> has cared for the past 10 years, why would they do so now?) and we do= n't >> >> need a SW state machine when the HW handles that for us, right? >> >>=20 >> >> As for chipidea, IIRC, that doesn't need a SW state machine either, b= ut >> >> I know very little about that IP and don't even have documentation on >> >> it. My understanding, however, is that chipidea behaves kinda like MU= SB, >> >> which changes roles automatically in HW based on ID pin state. >> > >> > Chipidea needs to set register for USB role manually. >>=20 >> okay, so chipidea has private control of role. Much like dwc3. That's go= od. >>=20 >> >> >>> + * @otg_dev: OTG controller device, if needs to be used with OTG= core. >> >> >>=20 >> >> >> do you really know of any platform which has a separate OTG contro= ller? >> >> >>=20 >> >> > >> >> > Andrew had pointed out in [1] that Tegra210 has separate blocks for= OTG, host >> >> > and gadget. >> >> > >> >> > [1] http://article.gmane.org/gmane.linux.ports.tegra/22969 >> >>=20 >> >> that's not an OTG controller, it's just a mux. No different than Inte= l's >> >> mux for swapping between XHCI and peripheral-only DWC3. >> >>=20 >> >> frankly, I would NEVER talk about OTG when type-C comes into play. Th= ey >> >> are two competing standards and, apparently, type-C is winning when it >> >> comes to role-swapping. >> >>=20 >> > >> > In fact, OTG is mis-used by people. Currently, if the port is dual-rol= e, >> > It will be considered as an OTG port. >>=20 >> That's because "dual-role" is a non-standard OTG. Seen as people really >> didn't care about OTG, we (linux-usb folks) ended up naturally referring >> to "non-standard OTG" as "dual-role". Just to avoid confusion. > > So, unless we use OTG FSM defined in OTG spec, we should not mention > "OTG" in Linux, right? to avoid confusion with the terminology, yes. With that settled, let's figure out how you can deliver what your marketting guys are asking of you. >> > You are right, if the connector is type-c, it will be called as "type-c >> > port" by people :) >>=20 >> oh no, that's not what I'm talking about. If you read Type-C and PD >> specs, they define their own method for data role swapping. USB OTG >> doesn't fit on top of a Type-C environment. It's not about what people >> will call it, it's really that OTG can't work on top of type-c. For >> starters, there's no ID pin ;-) > > I know type-c, yes, there is no relationship between OTG and type-c. okay, thanks =2D-=20 balbi --=-=-= Content-Type: application/pgp-signature; name="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJXaPhNAAoJEIaOsuA1yqRENHcP/jmghSW2gkCWzdckoE3R64hw TI0aAHygYkOEyuYM0j+mUoBUAlVkeXcvnQ3W9aiaCNdf5ot0eo+2qPWIpo/eTmXP SvMA9WkjJcDnz6aiuJmTK4QDiWt6h7AQk7hEc8N8kodp4sgqqW+iV+MmzSEFmUqZ kuwo0eP4hs0v1kNF8mlqXApBdo/my1mL7QfE2spfWoGVzTBUEc/M6123ZVSnawWm fcpHYQKz4SyRSJtb1unmkTgQtZH1l1bjjFHFM90Ri/c93u8rrZWqxeal6XPZuvtn EhRdMaESLyZibzT32jwLPxMPrdtiAIymxXNf+0XgqssmQwfDcWYs8qNsevGdKrnU Iz8Uc1CkQtsE302CKKeHXE2KkUFEQcNnEIJMD4EkawX0usfOSsWKXNM7Fx7r+Y60 +0iJCOAHNLCwnyjdQNKEeJOnQmePEmOoXSnwHPRemXG+lD+O9RbsRLIwv9z5DqPF 8IfCOqkLNpmtUMFzWClOq4lJGWfU3WPMc3aubCTuFSY5EEJOVswoCxoCM8EuTxrr RhVG9KkO5Lq2q6zwwoLuPT90VEs8YA9694F0+8sUVWi6AyJObsApfYzn3tq+Zkzn u+TLsu9AqgsGELzL4IEohbBhX6nr9aJYCqNjIrAZ+6fJk7jm42N5Vmcxm7upu7t1 YgFS9w8qxBL3tQnL8/a8 =AmA0 -----END PGP SIGNATURE----- --=-=-=-- -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html