Re: [PATCH] imx{5,6}: reset otg port after usb-serial boot

From: Sascha Hauer <s.hauer@pengutronix.de>
To: Michael Grzeschik <mgr@pengutronix.de>
Cc: Barebox List <barebox@lists.infradead.org>
Subject: Re: [PATCH] imx{5,6}: reset otg port after usb-serial boot
Date: Mon, 27 Aug 2018 10:29:59 +0200	[thread overview]
Message-ID: <20180827082959.dbpkqm7kvofembrh@pengutronix.de> (raw)
In-Reply-To: <20180827081322.bgtjhamviu5p7byd@pengutronix.de>

On Mon, Aug 27, 2018 at 10:13:22AM +0200, Michael Grzeschik wrote:
> On Mon, Aug 27, 2018 at 09:52:24AM +0200, Sascha Hauer wrote:
> > On Mon, Aug 27, 2018 at 09:47:41AM +0200, Michael Grzeschik wrote:
> > > On Fri, Aug 24, 2018 at 05:18:02PM -0300, Fabio Estevam wrote:
> > > > Hi Michael,
> > > > 
> > > > On Fri, Aug 24, 2018 at 4:55 PM, Michael Grzeschik <mgr@pengutronix.de> wrote:
> > > > 
> > > > > I get that it is not safe to toggle bits if the clock is not
> > > > > there. We could check for the bootsource. Is it possible to
> > > > > ensure that we are started by imx-usb-loader?
> > > > 
> > > > It is possible to determine if we have started via USB download mode.
> > > > 
> > > > Check the is_boot_from_usb() implementation in U-Boot for a reference.
> > > 
> > > Right, So it seems to be safe to reach for the phys registers on mx6.
> > > 
> > > On mx5 and similar we have a nop phy and the only way to
> > > communicate with it is through usbmisc, which is also in the
> > > register space that leads to a hang if one clock is missing.
> > > 
> > > I will search for another solutions on those SoCs.
> > 
> > It's not necessary to ask for the bootsource. You just have to enable
> > the clocks necessary to access the USB registers. Or the other way
> > round: When the clocks are not enabled already, you could assume we have
> > not booted from USB.
> 
> Right, I think enabling the clocks is a little bit more safe
> as we otherwise would need to ensure that nobody slips in
> a DCD that already ungates all clocks.

What could happen is that somebody *dis*abled the USB clocks in DCD. In
that case though the USB on the host will already be confused and we
already have lost - no need to do anything in that case.

Sascha

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