From: Albert Herranz on
The current SWIOTLB code uses a default of 64MB for the IO TLB area.
This size can be influenced using a kernel command line parameter "swiotlb".
Unfortunately, the parsing of the kernel command line is done _after_ the
swiotlb is initialized on some architectures.

This patch adds a new function swiotlb_set_default_size() which can be used
before swiotlb_init() to indicate the desired IO TLB area size in bytes.

This will be used later to implement a smaller IO TLB on the Nintendo Wii
video game console which just comes with 24MB + 64MB of RAM.

CC: linuxppc-dev(a)
CC: linux-kernel(a)
CC: x86(a)
CC: linux-ia64(a)
Signed-off-by: Albert Herranz <albert_herranz(a)>
include/linux/swiotlb.h | 2 ++
lib/swiotlb.c | 20 ++++++++++++++++++++
2 files changed, 22 insertions(+), 0 deletions(-)

diff --git a/include/linux/swiotlb.h b/include/linux/swiotlb.h
index 3954228..2af6a45 100644
--- a/include/linux/swiotlb.h
+++ b/include/linux/swiotlb.h
@@ -22,6 +22,8 @@ extern int swiotlb_force;
#define IO_TLB_SHIFT 11

+extern size_t __init swiotlb_set_default_size(size_t size);
extern void swiotlb_init(int verbose);

extern void *swiotlb_alloc_boot(size_t bytes, unsigned long nslabs);
diff --git a/lib/swiotlb.c b/lib/swiotlb.c
index 8f2dad9..dbeca50 100644
--- a/lib/swiotlb.c
+++ b/lib/swiotlb.c
@@ -117,6 +117,26 @@ setup_io_tlb_npages(char *str)
__setup("swiotlb=", setup_io_tlb_npages);
/* make io_tlb_overflow tunable too? */

+ * swiotlb_set_default_size() - set the default size for the IO TLB
+ * @size: size in bytes of the IO TLB
+ *
+ * A platform can use this function to change the default size of the
+ * IO TLB when the default of 64MB is not suitable.
+ * This function must be called before swiotlb_init().
+ *
+ * Note that on some platforms this is the only way to influence the
+ * size of the IO TLB, as the command line may be parsed _after_ the
+ * IO TLB is initialized.
+ */
+size_t __init swiotlb_set_default_size(size_t size)
+ size_t previous_size = io_tlb_nslabs << IO_TLB_SHIFT;
+ io_tlb_nslabs = size >> IO_TLB_SHIFT;
+ return previous_size;
void * __weak __init swiotlb_alloc_boot(size_t size, unsigned long nslabs)
return alloc_bootmem_low_pages(size);

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