linux-kernel - Re: [Patch v9 1/3] usb: dwc3: qcom: Add device tree binding

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Message-ID: <20140916182920.GF19010@saruman.home>
Date:	Tue, 16 Sep 2014 13:29:21 -0500
From:	Felipe Balbi <balbi@...com>
To:	Jack Pham <jackp@...eaurora.org>
CC:	Andy Gross <agross@...eaurora.org>, Felipe Balbi <balbi@...com>,
	<devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	Kishon Vijay Abraham I <kishon@...com>,
	Kumar Gala <galak@...eaurora.org>,
	<linux-arm-msm@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	"Ivan T. Ivanov" <iivanov@...sol.com>,
	Bjorn Andersson <bjorn.andersson@...ymobile.com>
Subject: Re: [Patch v9 1/3] usb: dwc3: qcom: Add device tree binding

Hi,

On Tue, Sep 16, 2014 at 11:15:43AM -0700, Jack Pham wrote:
> Hi Andy,
> 
> On Fri, Sep 12, 2014 at 02:28:06PM -0500, Andy Gross wrote:
> > +Example device nodes:
> > +
> > +		hs_phy: phy@...f8800 {
> > +			compatible = "qcom,dwc3-hs-usb-phy";
> > +			reg = <0x100f8800 0x30>;
> 
> Just wanted to point out that in our downstream code, the glue
> device/driver, i.e. "qcom,dwc3", does claim an entire register region
> that encompasses the same registers used by these PHYs. I noticed you're
> not adding a reg resource to the glue node below in this patchset. In
> order to allow multiple devices to use the overlapping regions, we avoid
> calling devm_ioremap_resource() and instead call devm_ioremap_nocache()
> directly which bypasses the request_mem_region() call, which I don't
> think is an entirely correct thing to do.
> 
> On the other hand I'm trying to think of use cases on our other SOCs
> (MSM8974, APQ8084) where the glue actually would need access to the same
> or adjacent IO registers that couldn't just be handled directly by these
> PHY drivers. Should we accommodate for the potential of overlapping
> regions or should we just hold the line here and maybe only expose with
> finer granularity the registers that will actually be needed by the PHYs
> & glue respectively?

I prefer to keep things separated. Glue only needs to access whatever
belongs to glue. If a register related to PHY settings, it should be in
the PHY address space.

cheers

-- 
balbi

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