linux-kernel - [PATCH v4] staging: rts5208: Convert kmap() to kmap_local

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Date:   Wed, 30 Mar 2022 16:33:31 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Benjamin Philip <benjamin.philip495@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Colin Ian King <colin.king@...el.com>,
        Samuel Sjöberg <info@...uelsjoberg.se>,
        Charlie Sands <sandsch@...thvilleschools.net>,
        linux-staging@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Dan Carpenter <dan.carpenter@...cle.com>, ira.weiny@...el.com,
        outreachy@...ts.linux.dev
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Subject: [PATCH v4] staging: rts5208: Convert kmap() to kmap_local_page()

The use of kmap() is being deprecated in favor of kmap_local_page()
where it is feasible.

With kmap_local_page(), the mapping is per thread, CPU local and not
globally visible. Therefore rtsx_stor_access_xfer_buf() is a function
where the use of kmap_local_page() in place of kmap() is correctly
suited.

Convert to kmap_local_page() but, instead of open coding it, use the
helpers memcpy_to_page() and memcpy_from_page().

Make a minor change to a comment related to scatter-gather.

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---

v1 -> v2: Rework the commit message and use the appropriate helpers
instead of open coding the use of kmap_local_page()/kunmap_local_page().
(Thanks to Ira Weiny <ira.weiny@...el.com>).

v2 -> v3: Use memcpy_{to,from}_page() arguments correctly.
(Thanks to Dan Carpenter <dan.carpenter@...cle.com>).

v3 -> v4: According to a suggestion by Ira Weiny, change the test
of a comment related to the use of scatter-gather.

 drivers/staging/rts5208/rtsx_transport.c | 12 +++++-------
 1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/drivers/staging/rts5208/rtsx_transport.c b/drivers/staging/rts5208/rtsx_transport.c
index 805dc18fac0a..d5ad49de4c56 100644
--- a/drivers/staging/rts5208/rtsx_transport.c
+++ b/drivers/staging/rts5208/rtsx_transport.c
@@ -55,9 +55,9 @@ unsigned int rtsx_stor_access_xfer_buf(unsigned char *buffer,
 		*offset += cnt;
 
 	/*
-	 * Using scatter-gather.  We have to go through the list one entry
-	 * at a time.  Each s-g entry contains some number of pages, and
-	 * each page has to be kmap()'ed separately.
+	 * Using scatter-gather. We have to go through the list one entry
+	 * at a time. Each s-g entry contains some number of pages which
+	 * have to be copied one at a time.
 	 */
 	} else {
 		struct scatterlist *sg =
@@ -92,13 +92,11 @@ unsigned int rtsx_stor_access_xfer_buf(unsigned char *buffer,
 			while (sglen > 0) {
 				unsigned int plen = min(sglen, (unsigned int)
 						PAGE_SIZE - poff);
-				unsigned char *ptr = kmap(page);
 
 				if (dir == TO_XFER_BUF)
-					memcpy(ptr + poff, buffer + cnt, plen);
+					memcpy_to_page(page, poff, buffer + cnt, plen);
 				else
-					memcpy(buffer + cnt, ptr + poff, plen);
-				kunmap(page);
+					memcpy_from_page(buffer + cnt, page, poff, plen);
 
 				/* Start at the beginning of the next page */
 				poff = 0;
-- 
2.34.1