linux-kernel - [patch 2.6.27-rc3] at91_mci: don't use coherent dma buffers

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Message-Id: <200808181607.21516.david-b@pacbell.net>
Date:	Mon, 18 Aug 2008 16:07:21 -0700
From:	David Brownell <david-b@...bell.net>
To:	Pierre Ossman <drzeus-mmc@...eus.cx>
Cc:	lkml <linux-kernel@...r.kernel.org>,
	Andrew Victor <linux@...im.org.za>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	Russell King <rmk@....linux.org.uk>
Subject: [patch 2.6.27-rc3] at91_mci: don't use coherent dma buffers

From: David Brownell <dbrownell@...rs.sourceforge.net>

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 <dbrownell@...rs.sourceforge.net>

---
 drivers/mmc/host/at91_mci.c |   20 ++++++++++++++++----
 1 file changed, 16 insertions(+), 4 deletions(-)

--- a/drivers/mmc/host/at91_mci.c
+++ b/drivers/mmc/host/at91_mci.c
@@ -621,12 +621,21 @@ static void at91_mci_send_command(struct
 				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);
 
 				at91_mci_write(host, ATMEL_PDC_TPR, host->physical_address);
@@ -694,7 +703,10 @@ static void at91_mci_completed_command(s
 	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;
 	}
 
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