On Fri, Mar 22, 2019 at 08:28:46AM -0500, Bin Liu wrote: > On Fri, Mar 22, 2019 at 02:09:53PM +0100, Maxime Ripard wrote: > > On Fri, Mar 22, 2019 at 07:46:22AM -0500, Bin Liu wrote: > > > On Thu, Mar 21, 2019 at 05:41:38PM +0100, Greg Kroah-Hartman wrote: > > > > On Thu, Mar 21, 2019 at 02:01:33PM +0100, Maxime Ripard wrote: > > > > > Hi, > > > > > > > > > > I'm reviving this thread a bit, because I encountered this bug today. > > > > > > > > > > On Thu, Mar 21, 2019 at 11:02:10AM +0100, Bin Liu wrote: > > > > > > On Sat, Apr 21, 2018 at 12:59:23PM +0200, Paul Kocialkowski wrote: > > > > > > > Hi, > > > > > > > > > > > > > > Le vendredi 20 avril 2018 à 09:25 -0500, Bin Liu a écrit : > > > > > > > > On Thu, Mar 29, 2018 at 01:57:24PM +0200, Paul Kocialkowski wrote: > > > > > > > > > Hi, > > > > > > > > > > > > > > > > > > On Thu, 2018-03-29 at 11:23 +0200, Maxime Ripard wrote: > > > > > > > > > > On Wed, Mar 28, 2018 at 11:52:13PM +0200, Paul Kocialkowski wrote: > > > > > > > > > > > This allows dual-role ports to be reported as having gadget mode > > > > > > > > > > > by > > > > > > > > > > > the > > > > > > > > > > > musb_has_gadget helper. This is required to enable MUSB at all > > > > > > > > > > > with > > > > > > > > > > > MUSB > > > > > > > > > > > glue layers that set the port mode to MUSB_PORT_MODE_DUAL_ROLE > > > > > > > > > > > at > > > > > > > > > > > init. > > > > > > > > > > > > > > > > > > > > > > Most notably, this allows calling musb_start when needed in the > > > > > > > > > > > virtual > > > > > > > > > > > MUSB root HUB, regardless of whether the current mode should be > > > > > > > > > > > gadget > > > > > > > > > > > or host. > > > > > > > > > > > > > > > > > > > > > > This fixes USB OTG on Allwinner devices that I could test it > > > > > > > > > > > with, > > > > > > > > > > > mainly A20 devices. > > > > > > > > > > > > > > > > > > > > > > Signed-off-by: Paul Kocialkowski > > > > > > > > > > > > > > > > > > > > Surely there's more to it than that. The gadget mode of A20 boards > > > > > > > > > > have been working in the past, including when compiling with mUSB > > > > > > > > > > setup as dual role. > > > > > > > > > > > > > > > > > > > > Is this a regression since a particular commit? Or is there > > > > > > > > > > another, > > > > > > > > > > deeper issue overlooked in the commit log? > > > > > > > > > > > > > > > > > > The root of the issue here is that musb_start is not called at any > > > > > > > > > point > > > > > > > > > without this patch. My understanding of the flow is the following: > > > > > > > > > when > > > > > > > > > the PHY detects that there was a VBUS/ID change, it will notify its > > > > > > > > > listeners (mainly the musb sunxi glue layer). This will then > > > > > > > > > schedule > > > > > > > > > the driver's work (sunxi_musb_work), which does nothing since the > > > > > > > > > SUNXI_MUSB_FL_ENABLED bit was never set. This bit is only set after > > > > > > > > > calling sunxi_musb_enable, which is called from > > > > > > > > > musb_platform_enable, > > > > > > > > > that originates from musb_start. > > > > > > > > > > > > > > > > > > Currently I see two places where musb_start is called: > > > > > > > > > * musb_virthub > > > > > > > > > * musb_gadget > > > > > > > > > > > > > > > > > > In the latter case, it is in turn called from udc_start, which > > > > > > > > > should > > > > > > > > > probably (correct me if I'm wrong) happen later in the call chain > > > > > > > > > than > > > > > > > > > ID/VBUS change notification time. > > > > > > > > > > > > > > > > I don't think it is correct that udc_start() is triggered by ID/VBUS > > > > > > > > events, but I don't have an Allwinner platform to verify the callflow. > > > > > > > > > > > > > > Yes you're right, I didn't make myself very clear here. I didn't > > > > > > > investigate the udc_start call path much since it was apparently not the > > > > > > > culprit. > > > > > > > > > > > > > > > Have you tried to load with a gadget driver? When a gadget function is > > > > > > > > bound to UDC, udc_start() is triggered, which in turn calls > > > > > > > > musb_start(). > > > > > > > > > > > > > > It does work under that scenario, although my used case here is using > > > > > > > musb with DUAL_ROLE but no gadget driver loaded. That it, I want the > > > > > > > musb_start call to originate from the virtual hub, not from the gadget > > > > > > > side. > > > > > > > > > > > > > > > > In the former case, musb_start is called in the root controller hub > > > > > > > > > control, when setting the USB_PORT_FEAT_POWER feature. This looks > > > > > > > > > perfectly legit and IMO this is where it should be initially calling > > > > > > > > > musb_start in the dual role case. The kernel is indeed setting the > > > > > > > > > > > > > > > > No actually. A dual-role port should be in b_idle state by default, so > > > > > > > > logically all actions should go to the gadget path until the port > > > > > > > > switches to host mode. > > > > > > > > > > > > > > It makes sense that the port should be in b_idle state by default, but > > > > > > > here it fails to switch to host mode when the ID pin detects that it > > > > > > > should. Or does b_idle state entail that a gadget must be loaded (per > > > > > > > the USB spec), and thus nothing should (ever) happen until that happens? > > > > > > > > > > > > > > I find it really odd to need a gadget device to trigger host mode. > > > > > > > This patch does fix the issue, but I am puzzled as to why it is needed > > > > > > > in the first place. The comment above it mentions that "In OTG mode we > > > > > > > have to wait until we loaded a gadget. We don't really need a gadget if > > > > > > > we operate as a host but we should not start a session as a device > > > > > > > without a gadget or else we explode.", which is apparently compatible > > > > > > > with my use case: a gadget is not really needed and I'm not trying to > > > > > > > start a session as a device without a gadget loaded. > > > > > > > > > > > > > > What do you think? > > > > > > > > > > > > Okay, this came down to an argument that whether we should require > > > > > > loading a gadget driver on a dual-role port to work in host mode, > > > > > > which is currently required on musb since a long long time ago. > > > > > > > > > > > > I understand the requirement is kinda unnecessary, but since it already > > > > > > exists on musb stack for a long time, I don't plan to change it. Because I > > > > > > cannot think of a use case in real products that doesn't automatically > > > > > > load a gadget function on the dual-role port. > > > > > > > > > > > > If you can explain a use case in real world (not a engineering lab) that > > > > > > the gadget driver will not be loaded at linux booting up, but later > > > > > > based on user's input, I will reconsider my decision. To remove this > > > > > > requirement from musb stack, the work is more than this patch. > > > > > > > > > > I have one for you: we're working on a device that boots pretty fast, > > > > > and therefore are pushing as much things as we can to modules. It > > > > > includes gadgets, the musb driver and glue, etc. That doesn't sound > > > > > way very different from what a generic distro would do as well. > > > > > > > > > > At boot, the various modules for the hardware are loaded > > > > > automatically: the musb glue, the musb core, our USB PHY, etc. We end > > > > > up in a situation where the musb driver is loaded and reported to work > > > > > properly. The USB cable to the OTG port (in peripheral) might or might > > > > > not be connected, it's kind of irrelevant. > > > > > > > > > > The gadgets, however, are not loaded automatically. > > > > > > > > > > Now comes a user that wants to use musb as a host, and connect a > > > > > proper USB adapter, that wires the ID pin properly. In our case, the > > > > > phy detects it, reports the mode change, and .... nothing. > > > > > > > > > > That doesn't really look like an engineering lab setup to me. > > > > > > > > I agree, that sounds like a valid setup. > > > > > > > > Also realize that Android is pushing to have all drivers as modules, so > > > > you will start to see a whole lot more devices out there be modular > > > > instead of statically built kernels. So issues like this are good to > > > > resolve :) > > > > > > This issue here is not related to building all drivers as modules. Today > > > we already have all musb related drivers including gadget drivers in > > > modules. > > > > > > The issue discussed here is that when musb is configured in dual-role > > > mode (dr_mode = 'otg' in dts), a gadget driver has to be bound to the > > > udc to make musb working in host mode. > > > > > > I never disagree it is not ideal, but I consider it is minor - since the > > > port is configured to dual-role mode, it is intended to work in > > > peripheral mode, then why not automatically load the gadget driver when > > > linux boots up. > > Again, think about an embedded product, That's all I'm thinking about. > if dr_mode is 'otg' which indicates the peripheral mode will be used > at some point No, it indicates that it *might* be used at some point, based on a number of external factors, including: - Whether or not the user has plugged something in the connected USB connector - If they did so, how the ID pin has been wired (and therefore, is a device or a host on the other end) - And how the system designer decided to configure their kernel and userspace. > when and how to load the gadget driver if it is not loaded > automatically when Linux boots up? the end user doesn't have access > to the console. An application could load it. And really, we start seeing SoCs in more and more pc-like devices, including with mUSB, so I don't think we should be making assumptions here. How do you think Fedora, Ubuntu or Debian would behave here? > > Because no other controller requires it and therefore it's not > > standard and violates the principle of least surprise? > > I know no other controller does this, but this doesn't mean it is not > standard. I'm pretty sure that would be the definition of "standard", or of a norm at least. > > And even without taking this into account, there's also the fact that > > while the *hardware* can do dual role, the software might decide > > otherwise. If I don't want to have support for any gadget (at all) in > > the end system, then why should I be forced to compile and load > > something I don't even want to use in the first place? > > then dr_mode should be set to 'host' instead, you don't have to load a > gadget if peripheral mode will never be used. No. The hardware is perfectly capable of using OTG. The software has been configured not to. Maxime -- Maxime Ripard, Bootlin Embedded Linux and Kernel engineering https://bootlin.com