linux-kernel - Re: [PATCH 24/32] dmaengine: ste_dma40: Supply full Device Tree parsing support

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Message-Id: <201304181306.34835.arnd@arndb.de>
Date:	Thu, 18 Apr 2013 13:06:34 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	linus.walleij@...ricsson.com, Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <djbw@...com>,
	Per Forlin <per.forlin@...ricsson.com>,
	Rabin Vincent <rabin@....in>
Subject: Re: [PATCH 24/32] dmaengine: ste_dma40: Supply full Device Tree parsing support

On Thursday 18 April 2013, Lee Jones wrote:
> Using the new DMA DT bindings and API, we can register the DMA40 driver
> as Device Tree capable. Now, when a client attempts to allocate a
> channel using the DMA DT bindings via its own node, we are able to parse
> the request and allocate a channel in the correct manor.

s/manor/manner/ ?

> +Optional properties:
> +- interrupt-parent: Should be the phandle for the interrupt controller
> +  that services interrupts for this device

I would not bother listing the interrupt-parent.

> +Clients
> +Required properties:
> +- dmas: Comma seperated list of dma channel requests
> +- dma-names: Names of the aforementioned requested channels
> +
> +Each dmas request consists of 4 cells:
> +  1. A phandle pointing to the DMA controller
> +  2. The DMA request line number (only when 'use fixed channel' is set)
> +  3. Device Type
> +  4. A 32bit mask specifying; mode, direction and endianess [NB: This list will grow]
> +        bits 1-2: Mode:
> +          00: Logical
> +          01: Physical
> +          10: Operation
> +          11: Undefined - will most likely return an error

The statement "will most likely return an error" is not very
specification-like. ;-) Maybe better call it "reserved".

What is actually an "Operation" channel? Do we need it for slaves?


> +        bits 3-4: Direction:
> +          00: Mem to Mem
> +          01: Mem to Dev
> +          10: Dev to Mem
> +          11: Dev to Dev

For slave channels, we only need mem-to-dev and dev-to-mem, so I would
use only one bit here.

> +        bit 5: Endianess:
> +           0: Little endian
> +           1: Big endian
> +        bit 6: Use fixed channel:
> +           0: Use automatic channel selection
> +           1: Use DMA request line number

I think you have mixed up the "device type" and "request line number".

The request line is what identifies the slave device (which you call
the device type), and I would put that number first.

	Arnd

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