linux-kernel - [PATCH, v3] x86: Adjust GFP mask handling for coherent allocations

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Date:	Sun, 8 Nov 2009 12:12:14 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Takashi Iwai <tiwai@...e.de>,
	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Jan Beulich <JBeulich@...ell.com>, tglx@...utronix.de,
	hpa@...or.com, linux-kernel@...r.kernel.org,
	jbarnes@...tuousgeek.org
Subject: [PATCH, v3] x86: Adjust GFP mask handling for coherent allocations


* Takashi Iwai <tiwai@...e.de> wrote:

> At Wed, 04 Nov 2009 12:28:39 +0000,
> Jan Beulich wrote:
> > 
> > Rather than forcing GFP flags and DMA mask to be inconsistent, GFP
> > flags should be determined even for the fallback device through
> > dma_alloc_coherent_mask()/dma_alloc_coherent_gfp_flags(). This
> > restores 64-bit behavior as it was prior to commits
> > 8965eb19386fdf5ccd0ef8b02593eb8560aa3416 and
> > 4a367f3a9dbf2e7ffcee4702203479809236ee6e (not sure why there are two of
> > them), where GFP_DMA was forced on for 32-bit, but not for 64-bit, with
> > the slight adjustment that afaict even 32-bit doesn't need this without
> > CONFIG_ISA.
> > 
> > Signed-off-by: Jan Beulich <jbeulich@...ell.com>
> > Cc: Takashi Iwai <tiwai@...e.de>
> 
> Acked-by: Takashi Iwai <tiwai@...e.de>

Jesse, mind picking this up for .32?

I've attached below a slightly cleaned up version of the patch, with 
Takashi's ack added.

Thanks,

	Ingo

------------------>
Subject: x86: Adjust GFP mask handling for coherent allocations
From: "Jan Beulich" <JBeulich@...ell.com>
Date: Wed, 04 Nov 2009 12:28:39 +0000

Rather than forcing GFP flags and DMA mask to be inconsistent,
GFP flags should be determined even for the fallback device
through dma_alloc_coherent_mask()/dma_alloc_coherent_gfp_flags().

This restores 64-bit behavior as it was prior to commits
8965eb19386fdf5ccd0ef8b02593eb8560aa3416 and
4a367f3a9dbf2e7ffcee4702203479809236ee6e (not sure why there are
two of them), where GFP_DMA was forced on for 32-bit, but not
for 64-bit, with the slight adjustment that afaict even 32-bit
doesn't need this without CONFIG_ISA.

Signed-off-by: Jan Beulich <jbeulich@...ell.com>
Acked-by: Takashi Iwai <tiwai@...e.de>
Cc: Jesse Barnes <jbarnes@...tuousgeek.org>
LKML-Reference: <4AF18187020000780001D8AA@....id2.novell.com>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
---
 arch/x86/include/asm/dma-mapping.h |   10 +++++++---
 arch/x86/kernel/pci-dma.c          |    6 ++----
 2 files changed, 9 insertions(+), 7 deletions(-)

Index: tip/arch/x86/include/asm/dma-mapping.h
===================================================================
--- tip.orig/arch/x86/include/asm/dma-mapping.h
+++ tip/arch/x86/include/asm/dma-mapping.h
@@ -14,6 +14,12 @@
 #include <asm/swiotlb.h>
 #include <asm-generic/dma-coherent.h>
 
+#ifdef CONFIG_ISA
+# define ISA_DMA_BIT_MASK DMA_BIT_MASK(24)
+#else
+# define ISA_DMA_BIT_MASK DMA_BIT_MASK(32)
+#endif
+
 extern dma_addr_t bad_dma_address;
 extern int iommu_merge;
 extern struct device x86_dma_fallback_dev;
@@ -124,10 +130,8 @@ dma_alloc_coherent(struct device *dev, s
 	if (dma_alloc_from_coherent(dev, size, dma_handle, &memory))
 		return memory;
 
-	if (!dev) {
+	if (!dev)
 		dev = &x86_dma_fallback_dev;
-		gfp |= GFP_DMA;
-	}
 
 	if (!is_device_dma_capable(dev))
 		return NULL;
Index: tip/arch/x86/kernel/pci-dma.c
===================================================================
--- tip.orig/arch/x86/kernel/pci-dma.c
+++ tip/arch/x86/kernel/pci-dma.c
@@ -45,12 +45,10 @@ int iommu_pass_through __read_mostly;
 dma_addr_t bad_dma_address __read_mostly = 0;
 EXPORT_SYMBOL(bad_dma_address);
 
-/* Dummy device used for NULL arguments (normally ISA). Better would
-   be probably a smaller DMA mask, but this is bug-to-bug compatible
-   to older i386. */
+/* Dummy device used for NULL arguments (normally ISA). */
 struct device x86_dma_fallback_dev = {
 	.init_name = "fallback device",
-	.coherent_dma_mask = DMA_BIT_MASK(32),
+	.coherent_dma_mask = ISA_DMA_BIT_MASK,
 	.dma_mask = &x86_dma_fallback_dev.coherent_dma_mask,
 };
 EXPORT_SYMBOL(x86_dma_fallback_dev);
--
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