linux-kernel - Re: [PATCH 8/8] phy: add driver for TI TUSB1210 ULPI PHY

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Date:	Fri, 30 Jan 2015 10:33:52 -0600
From:	Felipe Balbi <balbi@...com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
CC:	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Baolu Lu <baolu.lu@...ux.intel.com>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	Kishon Vijay Abraham I <kishon@...com>
Subject: Re: [PATCH 8/8] phy: add driver for TI TUSB1210 ULPI PHY

On Fri, Jan 30, 2015 at 08:20:38AM -0800, David Cohen wrote:
> On Fri, Jan 30, 2015 at 11:29:56AM +0200, Heikki Krogerus wrote:
> > Hi,
> > 
> > > > You can't really compare a bus like i2c, which can't enumerate devices
> > > > natively, to ULPI which can.
> > > 
> > > why not ? The BIOS might not need to use the PHY (or USB) at all, it can
> > > very well decide to never turn it on, right ?
> > 
> > If ULPI was seen as a bus, then no. BIOS would have definitely left
> > the PHY on. In fact, if we would have just asked the BIOS writers to
> > leave it on, they would not have any problem with that, even without
> > the bus.
> 
> That's a really wrong assumption. ULPI bus depends on dwc3 to be
> functional and dwc3 depends on phy to be functional to complete its
> power on sequence. We can't ask BIOS to let both up and running all the
> time.
> 
> FWIW we *cannot* rely on ULPI bus enumeration to probe ULPI devices,
> because it requires the ULPI device to be previously functional which
> can't happen before the enumeration. Even if we ask BIOS to let phy
> functional after boot, what happens when we remove modules and load it
> again? Should we ask BIOS to power on the components again in order to
> probe and power it on? It's a circular dependency you're creating.

do we need both CS and RESET for phy to be functional ? Since we need
PHY functional during ulpi bus enumeration phase, the only way would be
to have the ULPI bus code itself grab those GPIOs (as long as it's
gpiod_get_optional() we should be fine) and toggle them before
enumerating the bus.

The only problem is doing that for every driver_register() :-s

-- 
balbi

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