linux-kernel - Re: Disable bus's drivers_autoprobe before rootfs has mounted

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Message-ID: <20140612165317.GD21753@saruman.home>
Date:	Thu, 12 Jun 2014 11:53:17 -0500
From:	Felipe Balbi <balbi@...com>
To:	Peter Chen <peter.chen@...escale.com>
CC:	Felipe Balbi <balbi@...com>, Greg KH <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Matt Porter <matt.porter@...aro.org>
Subject: Re: Disable bus's drivers_autoprobe before rootfs has mounted

On Thu, Jun 12, 2014 at 03:02:12PM +0800, Peter Chen wrote:
> On Wed, Jun 11, 2014 at 02:36:27PM -0500, Felipe Balbi wrote:
> > On Wed, Jun 11, 2014 at 11:29:57AM +0800, Peter Chen wrote:
> > > On Tue, Jun 10, 2014 at 11:35:07PM -0500, Felipe Balbi wrote:
> > > > Hi,
> > > > 
> > > > On Tue, Jun 10, 2014 at 09:10:00PM -0700, Greg KH wrote:
> > > > > > Let's take USB peripheral as an example, there is a device for
> > > > > > udc, and a device driver for usb gadget driver, at default, we want
> > > > > > the device to be bound to driver automatically, this is what
> > > > > > we have done now. But if there are more than one udcs and gadget
> > > > > > drivers (eg one B port for mass storage, another B port for usb ethernet),
> > > > > > the user may want to have specific binding (eg, udc-0 -> mass storage,
> > > > > > udc-1 -> usb ethernet), so the binding will be established
> > > > > > after rootfs has mounted. (This feature is implementing)
> > > > > 
> > > > > Then there better be a way to describe this on the kernel command line
> > > > > (i.e. module paramaters), right?  Which is a total mess, why not just
> > > > > not bind anything in this case and let the user pick what they want?
> > > > 
> > > > you can also blacklist all gadget drivers and manually probe them or -
> > > > get this - you can refrain from using gadget drivers and use libusbg to
> > > > build the gadget drivers out of raw usb functions, then bind them to the
> > > > UDC of your liking.
> > > > 
> > > 
> > > I am just worried if we change the behaviour of using gadget driver,
> > > can it be accepted by user? If you think it can be accepted if we can
> > > have some docs, we can implement manually binding for gadget driver
> > > from now on.
> > 
> > user shouldn't have to deal with direct module insertion/removal (unless
> > he's a developer and actually *wants* to do that). Docs are already in
> > tree. The entire configfs interface has been documented, it's based on
> > those documents that Matt started writing libusbg.
> > 
> > -- 
> > balbi
> 
> Yes, gadget-configfs is a good direction.
> 
> I would like to know your plan for other gadget drivers (g_mass_storage,
> g_webcam, etc)

they can be built dynamically too. We only provided a version of
g_mass_storage in order to avoid regressions. We can't simply remove
that driver from the kernel.

> All functions will be supported by configfs in future, and current
> driver will be deleted?

I don't think we will be able to delete legacy drivers, but they're all
supported through configfs. I guess only webcam is missing.

> - If yes, how to cover the user who still use the old file system?
> - If no, which binding way for udc and gadget driver will be used?

going forward, we want to stick with configfs.

-- 
balbi

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