[PATCH 1/5] dmaengine: mxs-dma: add dma support for i.MX23/28

Hi Shawn,

Shawn Guo writes:

On Tue, Feb 08, 2011 at 03:41:55PM +0100, Lothar Wa?mann wrote:

[...]

quoted

What's behinde the 'PIO' transfers is programming controller registers
via DMA along with the actual DMA data transfer. DMA_NONE simply
means, that the DMA transfer does only the register programming but
does not transfer any payload. The 'pio_words' are the values that are
being written to consecutive locations of e.g. the SPI controller
register address space.
The programming is actually done by DMA, in any case.

I'm waiting for this reply ;)

i.MX23/28 Reference Manual uses word "PIO" for the working mode that
Lothar has explained.  It seems that "PIO" in mxs-dma needs some more
documents.

It's true that mxs dma hardware is designed to program peripheral
registers along with data transfer with ccw chain.  But it's hard
for generic dmaengine model to implement that.  The client device
driver gets the data in scatter-gather list to transfer.  It requires
client driver to manipulate the sgl to get pio ccw inserted properly
to get the "along with" implemented.  This is not a reasonable
implementation to me.

I still chose to keep the pio mode in the implementation in "single
step" rather than "along with" way.  That means client driver has to
issue one dma request to program client device registers, and issue
another one to transfer data.  The natural thought is that the pio

which defeats the purpose of the whole thing. If the software has to
issue a single request for DMA to program the registers it could as
well directly write the registers without any DMA. The purpose of the
embedded 'PIO' transfers is, that you can set up a whole chain of
commands and associated data transfers and have that executed
without any further software intervention.

support can totally be saved with cpu programming.  But looking at
any mxs dma client device in reference manual, you will find it gets
two irq lines, irq_dma and irq_error.  For ssp (mmc) example, when
one mmc command is issued and completed without error, you have to
either polling ssp status register or use pio dma and irq_dma
interrupt to know the completion.  That's to say I keep the pio

You could use the SSP IRQ as well.


Lothar Wa?mann
-- 
___________________________________________________________

Ka-Ro electronics GmbH | Pascalstra?e 22 | D - 52076 Aachen
Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10
Gesch?ftsf?hrer: Matthias Kaussen
Handelsregistereintrag: Amtsgericht Aachen, HRB 4996

www.karo-electronics.de | info at karo-electronics.de
___________________________________________________________