linux-kernel - [PATCH 2/2] misc/xilinx_sdfec: Replace kmap() with kmap_local

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Message-Id: <20220901154408.23984-3-fmdefrancesco@gmail.com>
Date:   Thu,  1 Sep 2022 17:44:08 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Derek Kiernan <derek.kiernan@...inx.com>,
        Dragan Cvetic <dragan.cvetic@...inx.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Michal Simek <michal.simek@...inx.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Subject: [PATCH 2/2] misc/xilinx_sdfec: Replace kmap() with kmap_local_page()

kmap() is being deprecated in favor of kmap_local_page().

There are two main problems with kmap(): (1) It comes with an overhead as
the mapping space is restricted and protected by a global lock for
synchronization and (2) it also requires global TLB invalidation when the
kmap’s pool wraps and it might block when the mapping space is fully
utilized until a slot becomes available.

With kmap_local_page() the mappings are per thread, CPU local, can take
page faults, and can be called from any context (including interrupts).
It is faster than kmap() in kernels with HIGHMEM enabled. Furthermore,
the tasks can be preempted and, when they are scheduled to run again, the
kernel virtual addresses are restored and still valid.

Since its use in xilinx_sdfec.c is safe, replace kmap()i / kunmap() with
kmap_local_page() / kunmap_local().

Cc: "Venkataramanan, Anirudh" <anirudh.venkataramanan@...el.com>
Suggested-by: Ira Weiny <ira.weiny@...el.com>
Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 drivers/misc/xilinx_sdfec.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/misc/xilinx_sdfec.c b/drivers/misc/xilinx_sdfec.c
index 4b1d82ae7312..cb9506f9cbd0 100644
--- a/drivers/misc/xilinx_sdfec.c
+++ b/drivers/misc/xilinx_sdfec.c
@@ -636,7 +636,7 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 	}

 	for (i = 0; i < nr_pages; i++) {
-		addr = kmap(pages[i]);
+		addr = kmap_local_page(pages[i]);
 		do {
 			xsdfec_regwrite(xsdfec,
 					base_addr + ((offset + reg) *
@@ -645,7 +645,7 @@ static int xsdfec_table_write(struct xsdfec_dev *xsdfec, u32 offset,
 			reg++;
 		} while ((reg < len) &&
 			 ((reg * XSDFEC_REG_WIDTH_JUMP) % PAGE_SIZE));
-		kunmap(pages[i]);
+		kunmap_local(addr);
 		unpin_user_page(pages[i]);
 	}
 	return 0;
-- 
2.37.2