[PATCH]: [MPC5200] Add ATA DMA support

[Tim Yamin]

This patch adds MDMA/UDMA support (using BestComm for DMA) on the MPC5200
platform.

Based heavily on previous work by Freescale (Bernard Kuhn, John Rigby)
and Domen Puncer.

Using a SanDisk Extreme IV CF card I get read speeds of approximately
26.70 MB/sec.

The BestComm ATA task priority was changed to maximum in bestcomm_priv.h;
this fixes a deadlock issue I was experiencing when heavy DMA was
occuring on both the ATA and Ethernet BestComm tasks, e.g. when
downloading a large file over a LAN to disk.

There's also what I believe to be a hardware bug if you have high levels
of BestComm ATA DMA activity along with heavy LocalPlus Bus activity;
the address bus seems to sometimes get corrupted with ATA commands while
the LocalPlus Bus operation is still active (i.e. Chip Select is asserted).

I've asked Freescale about this but have not received a reply yet -- if
anybody from Freescale has any ideas please contact me; I can supply some
analyzer traces if needed. Therefore, for now, do not enable DMA if you
need reliable LocalPlus Bus unless you do a fixup in your driver as
follows:

Locking example:

        while (test_and_set_bit(0, &pata_mpc52xx_ata_dma_lock) != 0)
        {
                struct bcom_task_2 *tsk = pata_mpc52xx_ata_dma_task;

                if(bcom_buffer_done_2(tsk))
                        return 1;
        }

	return 0;

(Save the return value to `flags`)

Unlocking example:

        if(flags == 0)
                clear_bit(0, &pata_mpc52xx_ata_dma_lock);

Comments and testing would of course be very welcome.

Thanks,

Signed-off-by: Tim Yamin <plasm at roo.me.uk>
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