linux-kernel - Re: [PATCH 5/5] Add DMA engine driver for Freescale MPC85xx processors.

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Date:	Sun, 9 Sep 2007 15:10:12 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Timur Tabi" <timur@...escale.com>
Cc:	"Zhang Wei" <wei.zhang@...escale.com>, shannon.nelson@...el.com,
	linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
	paulus@...ba.org
Subject: Re: [PATCH 5/5] Add DMA engine driver for Freescale MPC85xx processors.

On 9/9/07, Timur Tabi <timur@...escale.com> wrote:
> Dan Williams wrote:
>
> > This routine implies that there is a piece of code somewhere that
> > wants to select which channels it can use.  A similar effect can be
> > achieved by registering a dma_client with the dmaengine interface
> > ('dma_async_client_register').  Then when the client code makes a call
> > to 'dma_async_client_chan_request' it receives a 'dma_event_callback'
> > for each channel in the system.  It will also be asynchronously
> > notified of channels entering and leaving the system.  The goal is to
> > share a common infrastructure for channel management.
>
> Are you familiar with the "flat device tree" used for PowerPC systems?  The
> "piece of code somewhere" is the device tree subsystem that parses the device
> tree, which is compiled from the .dts files in arch/powerpc/boot/dts.
>
> The FDT is how PowerPC systems specify hardware configuration.  In the case of
> 85xx, the FDT contains entries for each DMA device (typically 2), and the
> entries contain sub-entries for each DMA channel as well as the address of the
> register sets for each channel.
>
Ahh, ok then this code is replacing what would normally be handled by
the PCI bus enumeration code, or the platform device registrations for
iop-adma in arch/arm/mach-iop13xx.  Sorry for the noise with this
comment.

> --
> Timur Tabi
> Linux Kernel Developer @ Freescale
> -

Thanks,
Dan
-
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