Grant Grundler wrote:
On Thu, May 1, 2008 at 11:09 PM, Mark Lord <liml@xxxxxx> wrote:
When performing EH, it is recommended to wait for the EDMA engine
to empty out requests-in-progress before disabling EDMA.
Introduce code to poll the EDMA_STATUS register for idle/empty bits
before disabling EDMA. For non-EH operation, this will normally exit
without delay, other than the register read.
..
+static void mv_wait_for_edma_empty_idle(struct ata_port *ap)
+{
+ void __iomem *port_mmio = mv_ap_base(ap);
+ const u32 empty_idle = (EDMA_STATUS_CACHE_EMPTY |
EDMA_STATUS_IDLE);
+ const int per_loop = 5, timeout = (15 * 1000 / per_loop);
I reccomend setting per_loop to 10 or 20 at least. 5us is not very long.
It takes about 1us to do an MMIO read. Each additional MMIO read will exacerbate
the problem of DMA not finishing since MMIO reads interfere with DMA streams.
Also can you add a comment why 15ms is right amount of time to wait?
..
I would, if I knew. That's just a random number.
My own timings with a handful of drives here indicated
that it takes a few hundred microseconds worst case,
so I just picked a bigger number to start with.
No rationale == no comment in the original.
But if you have a good theory for what that number ought to be,
then go for it -- just patch it and stick an explanation in.
Thanks.
BTW, I have no idea when EDMA stops on it's own or if we could
safely get EDMA to stop "prematurely" (e.g. disable PCI Bus Master).
..
I don't know what you're talking about there.
???
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