linux-kernel - Re: Problems with Freescale DMA driver

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Message-ID: <48D8F73A.4050004@freescale.com>
Date:	Tue, 23 Sep 2008 09:03:38 -0500
From:	Timur Tabi <timur@...escale.com>
To:	Ira Snyder <iws@...o.caltech.edu>
CC:	Dan Williams <dan.j.williams@...el.com>,
	linux-kernel@...r.kernel.org, maciej.sosnowski@...el.com,
	leoli@...escale.com, zw@...kernel.org,
	Kumar Gala <kumar.gala@...escale.com>
Subject: Re: Problems with Freescale DMA driver

Ira Snyder wrote:

> When your patch makes it in, you should probably add the cell-index to
> all of the dts files that are missing them.

Ah, I see that Kumar added a bunch of DMA nodes back in June and forgot the
cell-index properties.

> I was not able to cause the DMA controller to copy bad data. Perhaps the
> kernel just had a bug at the time. It was still relatively early on in
> the development cycle.

dmatest runs all the time, so it's possible that it's eating up DMA resources.
Try running your tests without CONFIG_DMATEST.

> In a related note, I've been somewhat following the discussion on LKML
> about creating an API for requesting a single DMA channel. This would be
> great in a driver I've written for PCI communication over a backplane.
> (I have a test board running in PCI Agent mode. It creates a virtual
> ethernet interface that passes data over the PCI bus.)

PCI devices should not be using generic DMA resources, so I don't see how this
would apply.

> Also, are there any plans to support the external start feature on the
> 83XX parts? (According to my datasheet, it is supported.) I will be
> using this feature in a driver I will be starting fairly soon.

External start is very device-specific, so I don't see how a generic DMA driver,
which is intended only for memory-to-memory DMA operations, can coordinate with
an external master.

-- 
Timur Tabi
Linux kernel developer at Freescale
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