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From:   "Isaac J. Manjarres" <isaacm@codeaurora.org>
To:     will@kernel.org, robin.murphy@arm.com, joro@8bytes.org
Cc:     "Isaac J. Manjarres" <isaacm@codeaurora.org>, pdaly@codeaurora.org,
        pratikp@codeaurora.org, linux-arm-kernel@lists.infradead.org,
        iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org
Subject: [PATCH 1/5] iommu/io-pgtable: Introduce map_sg() as a page table op
Date:   Fri,  8 Jan 2021 17:50:27 -0800
Message-Id: <1610157031-26301-2-git-send-email-isaacm@codeaurora.org>
In-Reply-To: <1610157031-26301-1-git-send-email-isaacm@codeaurora.org>
References: <1610157031-26301-1-git-send-email-isaacm@codeaurora.org>
Precedence: bulk

While mapping a scatter-gather list, iommu_map_sg() calls
into the IOMMU driver through an indirect call, which can
call into the io-pgtable code through another indirect call.

This sequence of going through the IOMMU core code, the IOMMU
driver, and finally the io-pgtable code, occurs for every
element in the scatter-gather list, in the worse case, which
is not optimal.

Introduce a map_sg callback in the io-pgtable ops so that
IOMMU drivers can invoke it with the complete scatter-gather
list, so that it can be processed within the io-pgtable
code entirely, reducing the number of indirect calls, and
boosting overall iommu_map_sg() performance.

Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
---
 include/linux/io-pgtable.h | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/include/linux/io-pgtable.h b/include/linux/io-pgtable.h
index ea727eb..6d0e731 100644
--- a/include/linux/io-pgtable.h
+++ b/include/linux/io-pgtable.h
@@ -147,6 +147,9 @@ struct io_pgtable_cfg {
  * struct io_pgtable_ops - Page table manipulation API for IOMMU drivers.
  *
  * @map:          Map a physically contiguous memory region.
+ * @map_sg:       Map a scatter-gather list of physically contiguous memory
+ *                chunks. The mapped pointer argument is used to store how
+ *                many bytes are mapped.
  * @unmap:        Unmap a physically contiguous memory region.
  * @iova_to_phys: Translate iova to physical address.
  *
@@ -156,6 +159,9 @@ struct io_pgtable_cfg {
 struct io_pgtable_ops {
 	int (*map)(struct io_pgtable_ops *ops, unsigned long iova,
 		   phys_addr_t paddr, size_t size, int prot, gfp_t gfp);
+	int (*map_sg)(struct io_pgtable_ops *ops, unsigned long iova,
+		      struct scatterlist *sg, unsigned int nents, int prot,
+		      gfp_t gfp, size_t *mapped);
 	size_t (*unmap)(struct io_pgtable_ops *ops, unsigned long iova,
 			size_t size, struct iommu_iotlb_gather *gather);
 	phys_addr_t (*iova_to_phys)(struct io_pgtable_ops *ops,
-- 
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