linux-kernel - Re: [PATCH v6 03/25] usb: ulpi: Support device discovery via DT

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Date:   Thu, 19 Jan 2017 08:39:01 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Peter Chen <hzpeterchen@...il.com>
Cc:     Stephen Boyd <stephen.boyd@...aro.org>, linux-usb@...r.kernel.org,
        Felipe Balbi <balbi@...nel.org>, Arnd Bergmann <arnd@...db.de>,
        Neil Armstrong <narmstrong@...libre.com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        devicetree@...r.kernel.org, Peter Chen <peter.chen@....com>,
        Andy Gross <andy.gross@...aro.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v6 03/25] usb: ulpi: Support device discovery via DT

On Thu, Jan 19, 2017 at 02:33:49PM +0800, Peter Chen wrote:
> On Wed, Dec 28, 2016 at 02:56:49PM -0800, Stephen Boyd wrote:
> > The qcom HSIC ULPI phy doesn't have any bits set in the vendor or
> > product ID registers. This makes it impossible to make a ULPI
> > driver match against the ID registers. Add support to discover
> > the ULPI phys via DT help alleviate this problem. In the DT case,
> > we'll look for a ULPI bus node underneath the device registering
> > the ULPI viewport (or the parent of that device to support
> > chipidea's device layout) and then match up the phy node
> > underneath that with the ULPI device that's created.
> > 
> > The side benefit of this is that we can use standard properties
> > in the phy node like clks, regulators, gpios, etc. because we
> > don't have firmware like ACPI to turn these things on for us. And
> > we can use the DT phy binding to point our phy consumer to the
> > phy provider.
> > 
> > The ULPI bus code supports native enumeration by reading the
> > vendor ID and product ID registers at device creation time, but
> > we can't be certain that those register reads will succeed if the
> > phy is not powered up. To avoid any problems with reading the ID
> > registers before the phy is powered we fallback to DT matching
> > when the ID reads fail.
> > 
> > If the ULPI spec had some generic power sequencing for these
> > registers we could put that into the ULPI bus layer and power up
> > the device before reading the ID registers. Unfortunately this
> > doesn't exist and the power sequence is usually device specific.
> > By having the device matched up with DT we can avoid this
> > problem.
> > 
> > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > Acked-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
> > Cc: <devicetree@...r.kernel.org>
> > Acked-by: Rob Herring <robh@...nel.org>
> > Signed-off-by: Stephen Boyd <stephen.boyd@...aro.org>
> 
> Greg, is it ok I pick up this patch, and send it with chipidea
> changes together for 4.11-rc1 later?

No objection from me.

thanks,

greg k-h