Re: [PATCH 8/8] ARM: omap_hsmmc: remove platform data dma_mask and initialization

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On Thu, Apr 19, 2012 at 11:07:42AM -0700, Tony Lindgren wrote:
> * Russell King - ARM Linux <linux@xxxxxxxxxxxxxxxx> [120419 10:46]:
> > On Wed, Apr 18, 2012 at 06:39:14PM -0700, Tony Lindgren wrote:
> > > Cool, you almost got it. Got it working for n800 and 770 with the following
> > > patch. Only extremely light testing done now so careful with this patch too..
> > > 
> > > Had to hack in support for the src_port and dst_port that's needed for
> > > omap_set_dma_src/dest_params on omap1.
> > 
> > What's the relationship between these ports and the DMA request signal?
> > Is there a document which describes this?
> 
> It's the source and destination addresses bus port, so it's more related
> to the addresses than request signal. I guess routing of the DMA request
> signal is what it really does.
> 
> I'm now wondering if it might be possible to set it automatically based on
> source and destination address.
> 
> There's some information in the omap5912 trm on pages 717 and 718:
> 
> http://www.ti.com/litv/pdf/spru742
> 
> It says for CSDP source port "This field identifies the port originator of
> the transfer."

Is there a reason not to use EMIFF as for the memory port for any DMA
activity between a peripheral and system (kernel) memory?

It looks to me like TIPB is the right port to use for anything except
camera and LCD?

If that's true, we can solve the memory side of the problem very easily -
we know that prep_slave_sg() will always souce from system memory, so
the port for that will be known.

For the peripheral side of the transfer, I think we should case this on
the request signal as the combinations seem to be very limited - and it
looks like this knowledge is specific to the DMA controller rather than
the peripheral.

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