linux-kernel - Re: [PATCH 11/11] swiotlb: allow initialisation with pre-allocated bounce-buffer

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Date:	Tue, 2 Jun 2009 10:27:58 +0100
From:	Ian Campbell <Ian.Campbell@...citrix.com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"jeremy@...p.org" <jeremy@...p.org>, "okir@...e.de" <okir@...e.de>,
	"gregkh@...e.de" <gregkh@...e.de>, "mingo@...e.hu" <mingo@...e.hu>
Subject: Re: [PATCH 11/11] swiotlb: allow initialisation with pre-allocated
	bounce-buffer

On Tue, 2009-06-02 at 00:08 -0400, FUJITA Tomonori wrote:
> Please tell me a pointer to Xen code to use this patch. I think that
> we could have more clean interfaces.

Certainly. This is the relevant bit of my current WIP patch. I'm not
happy about the interaction with the global swiotlb/swiotlb_force flags
at the moment, I was planning to spend today figuring out something
nicer (hence its WIP status).

Ian.

diff --git a/drivers/pci/xen-iommu.c b/drivers/pci/xen-iommu.c
index 4918938..ca005d8 100644
--- a/drivers/pci/xen-iommu.c
+++ b/drivers/pci/xen-iommu.c
@@ -5,8 +5,11 @@
 #include <linux/module.h>
 #include <linux/version.h>
 #include <linux/scatterlist.h>
+#include <linux/swiotlb.h>
+#include <linux/dma-mapping.h>
 #include <linux/io.h>
 #include <linux/bug.h>
+#include <linux/bootmem.h>
 
 #include <xen/interface/xen.h>
 #include <xen/grant_table.h>
@@ -44,3 +47,33 @@ static phys_addr_t xen_dma_to_phys(struct device *hwdev, dma_addr_t daddr)
 	return machine_to_phys(XMADDR(daddr)).paddr;
 }
 
+
+static int max_dma_bits = 32;
+
+static void xen_swiotlb_fixup(void *buf, size_t size, unsigned long nslabs)
+{
+	int i, rc;
+	int dma_bits;
+
+	printk(KERN_DEBUG "xen_swiotlb_fixup: buf=%p size=%zu\n",
+		buf, size);
+
+	dma_bits = get_order(IO_TLB_SEGSIZE << IO_TLB_SHIFT) + PAGE_SHIFT;
+
+	i = 0;
+	do {
+		int slabs = min(nslabs - i, (unsigned long)IO_TLB_SEGSIZE);
+
+		do {
+			rc = xen_create_contiguous_region(
+				(unsigned long)buf + (i << IO_TLB_SHIFT),
+				get_order(slabs << IO_TLB_SHIFT),
+				dma_bits);
+		} while (rc && dma_bits++ < max_dma_bits);
+		if (rc)
+			panic(KERN_ERR "xen_create_contiguous_region failed\n");
+
+		i += slabs;
+	} while(i < nslabs);
+}
+
@@ -300,9 +340,42 @@ void __init xen_iommu_init(void)
 
 	dma_ops = &xen_dma_ops;
 
-	if (swiotlb) {
+	if (xen_initial_domain() || swiotlb_force) {
+		unsigned long bytes;
+		void *buffer, *overflow;
+		size_t default_size = 64 * (1<<20);	/* default to 64MB */
+
 		printk(KERN_INFO "Xen: Enabling DMA fallback to swiotlb\n");
+
+		swiotlb = 0; /* Avoid native swiotlb initialisation path. */
+		swiotlb_force = 0;
+
 		dma_ops = &xen_swiotlb_dma_ops;
+
+		if (!io_tlb_nslabs) {
+			io_tlb_nslabs = (default_size >> IO_TLB_SHIFT);
+			io_tlb_nslabs = ALIGN(io_tlb_nslabs, IO_TLB_SEGSIZE);
+		}
+
+		bytes = io_tlb_nslabs << IO_TLB_SHIFT;
+
+		/*
+		 * Get IO TLB memory. No need for low low pages under Xen.
+		 */
+		buffer = alloc_bootmem_pages(bytes);
+		if (!buffer)
+			panic("Cannot allocate SWIOTLB buffer");
+		xen_swiotlb_fixup(buffer, bytes, io_tlb_nslabs);
+
+		/*
+		 * Get the overflow emergency buffer
+		 */
+		overflow = alloc_bootmem(io_tlb_overflow);
+		if (!overflow)
+			panic("Cannot allocate SWIOTLB overflow buffer!\n");
+		xen_swiotlb_fixup(overflow, io_tlb_overflow, io_tlb_overflow >> IO_TLB_SHIFT);
+
+		swiotlb_init_with_buffer(bytes, buffer, overflow);
 	}
 }
 


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