linux-kernel - Re: [PATCH v2 1/9] of: Add NVIDIA Tegra XUSB mailbox binding

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Date:	Mon, 25 Aug 2014 12:48:23 -0600
From:	Stephen Warren <swarren@...dotorg.org>
To:	Andrew Bresticker <abrestic@...omium.org>,
	Thierry Reding <thierry.reding@...il.com>,
	linux-tegra@...r.kernel.org
CC:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Russell King <linux@....linux.org.uk>,
	Jassi Brar <jassisinghbrar@...il.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Arnd Bergmann <arnd@...db.de>,
	Kishon Vijay Abraham I <kishon@...com>,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH v2 1/9] of: Add NVIDIA Tegra XUSB mailbox binding

On 08/18/2014 11:08 AM, Andrew Bresticker wrote:
> Add device-tree bindings for the Tegra XUSB mailbox which will be used
> for communication between the Tegra xHCI controller's firmware and the
> host processor.

> diff --git a/Documentation/devicetree/bindings/mailbox/nvidia,tegra124-xusb-mbox.txt b/Documentation/devicetree/bindings/mailbox/nvidia,tegra124-xusb-mbox.txt

> +NVIDIA Tegra XUSB mailbox
> +=========================
> +
> +The Tegra XUSB mailbox is used by the Tegra xHCI controller's firmware to
> +communicate requests to the host and PHY drivers.
> +
> +Required properties:
> +--------------------
> + - compatible: Should be "nvidia,tegra124-xusb-mbox".
> + - reg: Address and length of the XUSB FPCI registers.
> + - interrupts: XUSB mailbox interrupt.
> + - #mbox-cells: Should be 1.  The specifier is the index of the mailbox to
> +   reference.  See <dt-bindings/mailbox/tegra-xusb-mailbox.h> for the list
> +   of valid values.

Is there a common mailbox binding somewhere? I couldn't find one. While 
the text above specifies the value for #mbox-cells, it doesn't specify 
the details of what the property is used for (i.e. there's no 
documentation of the consumer-side of this property, for parsing the 
mboxes property). Typically, that would be part of a subsystem's common 
binding document, and that document would be referenced here.

> diff --git a/include/dt-bindings/mailbox/tegra-xusb-mailbox.h b/include/dt-bindings/mailbox/tegra-xusb-mailbox.h

> +#define TEGRA_XUSB_MBOX_CHAN_HOST	0
> +#define TEGRA_XUSB_MBOX_CHAN_PHY	1

I can't work out how these values relate to hardware at all. Are they in 
fact properties of the particular firmware that's loaded into the XUSB 
module? If so, I don't think the DT should contain these values at all. 
I wonder if the individual MBOX_CMD_* values from patch 2 are any 
better, although I think those are also defined by the firmware, not the 
hardware?
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