mmc: at91_mci: don't use coherent dma buffers

At91_mci is abusing dma_free_coherent(), which may not be called with IRQs
disabled. I saw "mkfs.ext3" on an MMC card objecting voluminously as each
write completed:

WARNING: at arch/arm/mm/consistent.c:368 dma_free_coherent+0x2c/0x224()
[<c002726c>] (dump_stack+0x0/0x14) from [<c00387d4>] (warn_on_slowpath+0x4c/0x68)
[<c0038788>] (warn_on_slowpath+0x0/0x68) from [<c0028768>] (dma_free_coherent+0x2c/0x224)
r6:00008008 r5:ffc06000 r4:00000000
[<c002873c>] (dma_free_coherent+0x0/0x224) from [<c01918ac>] (at91_mci_irq+0x374/0x420)
[<c0191538>] (at91_mci_irq+0x0/0x420) from [<c0065d9c>] (handle_IRQ_event+0x2c/0x6c)
...

This bug has been around for a LONG time. The MM warning is from late
2005, but the driver merged a year later ... so I'm puzzled why nobody
noticed this before now.

The fix involves noting that this buffer shouldn't be DMA-coherent; it's
just used for normal DMA writes. So replace it with standard kmalloc()
buffering and DMA mapping calls.

This is the quickie fix. A better one would not rely on allocating large
bounce buffers. (Note that dma_alloc_coherent could have failed too, but
that case was ignored... kmalloc is a bit more likely to fail though.)

Signed-off-by: David Brownell <[e-mail]>
Acked-by: Pierre Ossman <[e-mail]>
Cc: Andrew Victor <[e-mail]>
Acked-by: Nicolas Ferre <[e-mail]>
Cc: Russell King <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/mmc/host/at91_mci.c

···
 				if (cpu_is_at91sam9260 () || cpu_is_at91sam9263())
 					if (host->total_length < 12)
 						host->total_length = 12;
-				host->buffer = dma_alloc_coherent(NULL,
-						host->total_length,
-						&host->physical_address, GFP_KERNEL);
+
+				host->buffer = kmalloc(host->total_length, GFP_KERNEL);
+				if (!host->buffer) {
+					pr_debug("Can't alloc tx buffer\n");
+					cmd->error = -ENOMEM;
+					mmc_request_done(host->mmc, host->request);
+					return;
+				}
 
 				at91_mci_sg_to_dma(host, data);
+
+				host->physical_address = dma_map_single(NULL,
+						host->buffer, host->total_length,
+						DMA_TO_DEVICE);
 
 				pr_debug("Transmitting %d bytes\n", host->total_length);
 
···
 	cmd->resp[3] = at91_mci_read(host, AT91_MCI_RSPR(3));
 
 	if (host->buffer) {
-		dma_free_coherent(NULL, host->total_length, host->buffer, host->physical_address);
+		dma_unmap_single(NULL,
+				host->physical_address, host->total_length,
+				DMA_TO_DEVICE);
+		kfree(host->buffer);
 		host->buffer = NULL;
 	}