linux-kernel - Re: [RFC patch] init default dma_ops to prepare intel_iommu

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Message-Id: <20090813121444W.fujita.tomonori@lab.ntt.co.jp>
Date:	Thu, 13 Aug 2009 12:15:46 +0900
From:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
To:	luming.yu@...il.com
Cc:	fujita.tomonori@....ntt.co.jp, dwmw2@...radead.org,
	fenghua.yu@...el.com, tony.luck@...el.com,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [RFC patch] init default dma_ops to prepare intel_iommu_init 
	failure

On Thu, 13 Aug 2009 10:24:20 +0800
Luming Yu <luming.yu@...il.com> wrote:

> On Thu, Aug 13, 2009 at 10:11 AM, FUJITA
> Tomonori<fujita.tomonori@....ntt.co.jp> wrote:
> > On Wed, 12 Aug 2009 17:20:11 +0800
> > Luming Yu <luming.yu@...il.com> wrote:
> >
> >> Hi there,
> >>
> >> On ia64 platform with dmar table and new upstream
> >> kernel(config_dmar_default_on enabled),
> >> if intel_iommu_init ends up without dma_ops initialized or other iommu
> >> failures.
> >> We got nothing to fall back. The following patch fixes it.
> >
> > Hmm, I think that the current code should work.
> 
> Without the patch, I encounters boot failure with the following .config
> 
> 162-CONFIG_IA64_GENERIC=y
> 163-# CONFIG_IA64_DIG is not set
> 164:# CONFIG_IA64_DIG_VTD is not set

Duh, yeah, intel_iommu_init() fails, it doesn't work.

X86 falls back into nommu_dam_ops but IA64 has nothing.

pci_swiotlb_init() can't set swiotlb to 1 or overwrite dma_ops? If it
sets swiotlb to 1, intel_iommu_init() fails.

A quick fix could be something like this:


diff --git a/arch/ia64/include/asm/swiotlb.h b/arch/ia64/include/asm/swiotlb.h
index dcbaea7..21b076e 100644
--- a/arch/ia64/include/asm/swiotlb.h
+++ b/arch/ia64/include/asm/swiotlb.h
@@ -5,6 +5,7 @@
 #include <linux/swiotlb.h>
 
 extern int swiotlb_force;
+extern struct dma_map_ops swiotlb_dma_ops;
 
 #ifdef CONFIG_SWIOTLB
 extern int swiotlb;
diff --git a/arch/ia64/kernel/pci-dma.c b/arch/ia64/kernel/pci-dma.c
index f6b1ff0..344d783 100644
--- a/arch/ia64/kernel/pci-dma.c
+++ b/arch/ia64/kernel/pci-dma.c
@@ -11,6 +11,7 @@
 #include <asm/iommu.h>
 #include <asm/machvec.h>
 #include <linux/dma-mapping.h>
+#include <asm/swiotlb.h>
 
 #include <asm/system.h>
 
@@ -47,8 +48,13 @@ extern struct dma_map_ops intel_dma_ops;
 
 static int __init pci_iommu_init(void)
 {
-	if (iommu_detected)
-		intel_iommu_init();
+	int ret;
+
+	if (iommu_detected) {
+		ret = intel_iommu_init();
+		if (ret)
+			dma_ops = &swiotlb_dma_ops;
+	}
 
 	return 0;
 }
diff --git a/arch/ia64/kernel/pci-swiotlb.c b/arch/ia64/kernel/pci-swiotlb.c
index 223abb1..ad164cf 100644
--- a/arch/ia64/kernel/pci-swiotlb.c
+++ b/arch/ia64/kernel/pci-swiotlb.c
@@ -46,12 +46,14 @@ void __init swiotlb_dma_init(void)
 
 void __init pci_swiotlb_init(void)
 {
-	if (!iommu_detected || iommu_pass_through) {
+	/* for fallback */
+	swiotlb_init();
+
+	if (!dma_ops) {
 #ifdef CONFIG_IA64_GENERIC
 		swiotlb = 1;
 		printk(KERN_INFO "PCI-DMA: Re-initialize machine vector.\n");
 		machvec_init("dig");
-		swiotlb_init();
 		dma_ops = &swiotlb_dma_ops;
 #else
 		panic("Unable to find Intel IOMMU");
--
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