linux-kernel - Re: [Xen-devel] [PATCH 03 of 38] swiotlb: allow architectures tooverride swiotlb pool allocation

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Date:	Fri, 14 Nov 2008 09:01:46 +0000
From:	"Jan Beulich" <jbeulich@...ell.com>
To:	"Jeremy Fitzhardinge" <jeremy@...p.org>
Cc:	"Ian Campbell" <ian.campbell@...rix.com>,
	"Ingo Molnar" <mingo@...e.hu>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	"Xen-devel" <xen-devel@...ts.xensource.com>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [Xen-devel] [PATCH 03 of 38] swiotlb: allow architectures
	 tooverride swiotlb pool allocation

Not directly related to this patch alone, but to the combined set of changes
to swiotlb: I don't see any handling of CONFIG_HIGHMEM here (or at least
a note that this a known limitation needing work). I mention this because
this was the largest part of the changes I had posted long ago to make
lib/swiotlb.c Xen-ready, and which got rejected due to their ugliness.

While perhaps less intrusive to take care of, I also didn't see an equivalent
of the range_straddles_page_boundary() logic, without which I can't see
how this would work in the common case.

Jan

>>> Jeremy Fitzhardinge <jeremy@...p.org> 13.11.08 20:10 >>>
Architectures may need to allocate memory specially for use with
the swiotlb.  Create the weak function swiotlb_alloc_boot() and
swiotlb_alloc() defaulting to the current behaviour.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>
Signed-off-by: Ian Campbell <ian.campbell@...rix.com>
Cc: Joerg Roedel <joerg.roedel@....com>
Cc: Jan Beulich <jbeulich@...ell.com>
Cc: Tony Luck <tony.luck@...el.com>
Cc: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
---
 include/linux/swiotlb.h |    3 +++
 lib/swiotlb.c           |   16 +++++++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -10,6 +10,9 @@
 extern void
 swiotlb_init(void);
 
+extern void *swiotlb_alloc_boot(size_t bytes, unsigned long nslabs);
+extern void *swiotlb_alloc(unsigned order, unsigned long nslabs);
+
 extern void
 *swiotlb_alloc_coherent(struct device *hwdev, size_t size,
 			dma_addr_t *dma_handle, gfp_t flags);
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -21,6 +21,7 @@
 #include <linux/mm.h>
 #include <linux/module.h>
 #include <linux/spinlock.h>
+#include <linux/swiotlb.h>
 #include <linux/string.h>
 #include <linux/types.h>
 #include <linux/ctype.h>
@@ -126,6 +127,16 @@
 __setup("swiotlb=", setup_io_tlb_npages);
 /* make io_tlb_overflow tunable too? */
 
+void * __weak swiotlb_alloc_boot(size_t size, unsigned long nslabs)
+{
+	return alloc_bootmem_low_pages(size);
+}
+
+void * __weak swiotlb_alloc(unsigned order, unsigned long nslabs)
+{
+	return (void *)__get_free_pages(GFP_DMA | __GFP_NOWARN, order);
+}
+
 /*
  * Statically reserve bounce buffer space and initialize bounce buffer data
  * structures for the software IO TLB used to implement the DMA API.
@@ -145,7 +156,7 @@
 	/*
 	 * Get IO TLB memory from the low pages
 	 */
-	io_tlb_start = alloc_bootmem_low_pages(bytes);
+	io_tlb_start = swiotlb_alloc_boot(bytes, io_tlb_nslabs);
 	if (!io_tlb_start)
 		panic("Cannot allocate SWIOTLB buffer");
 	io_tlb_end = io_tlb_start + bytes;
@@ -202,8 +213,7 @@
 	bytes = io_tlb_nslabs << IO_TLB_SHIFT;
 
 	while ((SLABS_PER_PAGE << order) > IO_TLB_MIN_SLABS) {
-		io_tlb_start = (char *)__get_free_pages(GFP_DMA | __GFP_NOWARN,
-		                                        order);
+		io_tlb_start = swiotlb_alloc(order, io_tlb_nslabs);
 		if (io_tlb_start)
 			break;
 		order--;



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