On 13/06/2019 11:20, Yoshihiro Shimoda wrote:
This patch adds a helper function whether a queue can merge
the segments by an IOMMU.
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@xxxxxxxxxxx>
---
block/blk-settings.c | 28 ++++++++++++++++++++++++++++
include/linux/blkdev.h | 2 ++
2 files changed, 30 insertions(+)
diff --git a/block/blk-settings.c b/block/blk-settings.c
index 45f2c52..4e4e13e 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -4,9 +4,11 @@
*/
#include <linux/bio.h>
#include <linux/blkdev.h>
+#include <linux/device.h>
#include <linux/gcd.h>
#include <linux/gfp.h>
#include <linux/init.h>
+#include <linux/iommu.h>
#include <linux/jiffies.h>
#include <linux/kernel.h>
#include <linux/lcm.h>
@@ -831,6 +833,32 @@ void blk_queue_write_cache(struct request_queue *q, bool wc, bool fua)
}
EXPORT_SYMBOL_GPL(blk_queue_write_cache);
+/**
+ * blk_queue_can_use_iommu_merging - configure queue for merging segments.
+ * @q: the request queue for the device
+ * @dev: the device pointer for dma
+ *
+ * Tell the block layer about the iommu merging of @q.
+ */
+bool blk_queue_can_use_iommu_merging(struct request_queue *q,
+ struct device *dev)
+{
+ struct iommu_domain *domain;
+
+ /*
+ * If the device DMA is translated by an IOMMU, we can assume
+ * the device can merge the segments.
+ */
+ if (!device_iommu_mapped(dev))
Careful here - I think this validates the comment I made when this
function was introduced, in that that name doesn't necesarily mean what
it sounds like it might mean - "iommu_mapped" was as close as we managed
to get to a convenient shorthand for "performs DMA through an
IOMMU-API-enabled IOMMU". Specifically, it does not imply that
translation is *currently* active; if you boot with "iommu=pt" or
equivalent this will still return true even though the device will be
using direct/SWIOTLB DMA ops without any IOMMU translation.
Robin.
+ return false;
+
+ domain = iommu_get_domain_for_dev(dev);
+ /* No need to update max_segment_size. see blk_queue_virt_boundary() */
+ blk_queue_virt_boundary(q, iommu_get_minimum_page_size(domain) - 1);
+
+ return true;
+}
+
static int __init blk_settings_init(void)
{
blk_max_low_pfn = max_low_pfn - 1;
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 592669b..4d1f7dc 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1091,6 +1091,8 @@ extern void blk_queue_dma_alignment(struct request_queue *, int);
extern void blk_queue_update_dma_alignment(struct request_queue *, int);
extern void blk_queue_rq_timeout(struct request_queue *, unsigned int);
extern void blk_queue_write_cache(struct request_queue *q, bool enabled, bool fua);
+extern bool blk_queue_can_use_iommu_merging(struct request_queue *q,
+ struct device *dev);
/*
* Number of physical segments as sent to the device.
