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Date: Fri, 29 Apr 2011 18:13:04 +0800
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To: linux-kernel@vger.kernel.org
CC: dan.j.williams@intel.com
Subject: Can I/OAT DMA engineer access PCI MMIO space
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I try to use ioatdam to copy data from system memory to pci MMIO space:

=======================
void mmio_copy(void *dst, void *src, size_t len)
struct async_submit_ctl submit;
struct memcpy_context ctx;

atomic_set(&ctx.cnt, 1);
init_completion(&ctx.cmp);
init_async_submit(&submit, ASYNC_TX_ACK, NULL,
done_memcpy, &ctx, NULL);

while (len) {
size_t clen = (len > PAGE_SIZE) ? PAGE_SIZE : len;
struct page *p_dst, *p_src;

p_dst = virt_to_page(dst);
p_src = virt_to_page(src);

atomic_inc(&ctx.cnt);

ntb_async_memcpy(p_dst, p_src, 0, 0, clen, &submit);

dst += clen;
src += clen;
len -= clen;
}

if (atomic_dec_and_test(&ctx.cnt))
return;

async_tx_issue_pending_all();
wait_for_completion(&ctx.cmp);
=================

If dst points to a memory space, the operation would pass.
But if dst points to a pci MMIO space, it failed with kernel oops.
It seems the code:
BUG_ON(is_ioat_bug(chanerr));
in drivers/dma/ioat/dma_v3.c, line 365 cause the oops.
Is there anyway to access pci MMIO space using ioat?
The datasheet says that ioat supports MMIO access.