Re: 2.6.26-rc1 regression: ISA DMA broken (bisected)

[Ingo Molnar]

* Ingo Molnar <mingo@xxxxxxx> wrote:

> good catch! Queued it up for testing. Jesse, do you concur?

here's the patch below, tidied up.

	Ingo

------------------------------->
Subject: x86/pci: fix broken ISA DMA
From: Takashi Iwai <tiwai@xxxxxxx>
Date: Fri, 09 May 2008 08:06:55 +0200

Rene Herman reported:

> commit 8779f2fc3b84ebb6c5181fb13d702e9944c16069
>
> "x86: don't try to allocate from DMA zone at first"
>
> breaks all of ISA DMA. Or all of ALSA ISA DMA at least. All
> ISA soundcards are silent following that commit -- no error
> messages, everything appears fine, just silence.

That patch is buggy. We had an implicit assumption that
dev = NULL for ISA devices that require 24bit DMA.

The recent work on x86 dma_alloc_coherent() breaks the ISA DMA buffer
allocation, which is represented by "dev = NULL" and requires 24bit
DMA implicitly.

Bisected-by: Rene Herman <rene.herman@xxxxxxxxxxxx>
Signed-off-by: Takashi Iwai <tiwai@xxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
---
 arch/x86/kernel/pci-dma.c |    8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

Index: linux-x86.q/arch/x86/kernel/pci-dma.c
===================================================================
--- linux-x86.q.orig/arch/x86/kernel/pci-dma.c
+++ linux-x86.q/arch/x86/kernel/pci-dma.c
@@ -386,11 +386,13 @@ dma_alloc_coherent(struct device *dev, s
 	if (dma_alloc_from_coherent_mem(dev, size, dma_handle, &memory))
 		return memory;
 
-	if (!dev)
+	if (!dev) {
 		dev = &fallback_dev;
+		gfp |= GFP_DMA;
+	}
 	dma_mask = dev->coherent_dma_mask;
 	if (dma_mask == 0)
-		dma_mask = DMA_32BIT_MASK;
+		dma_mask = (gfp & GFP_DMA) ? DMA_24BIT_MASK : DMA_32BIT_MASK;
 
 	/* Device not DMA able */
 	if (dev->dma_mask == NULL)
@@ -404,7 +406,7 @@ dma_alloc_coherent(struct device *dev, s
 	   larger than 16MB and in this case we have a chance of
 	   finding fitting memory in the next higher zone first. If
 	   not retry with true GFP_DMA. -AK */
-	if (dma_mask <= DMA_32BIT_MASK)
+	if (dma_mask <= DMA_32BIT_MASK && !(gfp & GFP_DMA))
 		gfp |= GFP_DMA32;
 #endif
 
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