linux-kernel - [PATCH] staging: media: atomisp: Use kmap_local_page() in hmm

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Message-Id: <20220413225531.9425-1-fmdefrancesco@gmail.com>
Date:   Thu, 14 Apr 2022 00:55:31 +0200
From:   "Fabio M. De Francesco" <fmdefrancesco@...il.com>
To:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Hans Verkuil <hverkuil-cisco@...all.nl>,
        Tsuchiya Yuto <kitakar@...il.com>,
        Martiros Shakhzadyan <vrzh@...h.net>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Ira Weiny <ira.weiny@...el.com>,
        outreachy@...ts.linux.dev
Cc:     "Fabio M. De Francesco" <fmdefrancesco@...il.com>
Subject: [PATCH] staging: media: atomisp: Use kmap_local_page() in hmm_store()

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

In file pci/hmm/hmm.c, function hmm_store() test if we are in atomic
context and, if so, it calls kmap_atomic(), if not, it calls kmap().

First of all, in_atomic() shouldn't be used in drivers. This macro
cannot always detect atomic context; in particular, it cannot know
about held spinlocks in non-preemptible kernels.

Notwithstanding what it is said above, this code doesn't need to care
whether or not it is executing in atomic context. It can simply use
kmap_local_page() / kunmap_local() that can instead do the mapping /
unmapping regardless of the context.

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

Convert the calls of kmap() / kunmap() and kmap_atomic() /
kunmap_atomic() to kmap_local_page() / kunmap_local() and drop the
unnecessary tests which test if the code is in atomic context.

Signed-off-by: Fabio M. De Francesco <fmdefrancesco@...il.com>
---
 drivers/staging/media/atomisp/pci/hmm/hmm.c | 14 ++------------
 1 file changed, 2 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/media/atomisp/pci/hmm/hmm.c b/drivers/staging/media/atomisp/pci/hmm/hmm.c
index 46ac082cd3f1..54188197c3dc 100644
--- a/drivers/staging/media/atomisp/pci/hmm/hmm.c
+++ b/drivers/staging/media/atomisp/pci/hmm/hmm.c
@@ -482,10 +482,7 @@ int hmm_store(ia_css_ptr virt, const void *data, unsigned int bytes)
 		idx = (virt - bo->start) >> PAGE_SHIFT;
 		offset = (virt - bo->start) - (idx << PAGE_SHIFT);

-		if (in_atomic())
-			des = (char *)kmap_atomic(bo->page_obj[idx].page);
-		else
-			des = (char *)kmap(bo->page_obj[idx].page);
+		des = (char *)kmap_local_page(bo->page_obj[idx].page);

 		if (!des) {
 			dev_err(atomisp_dev,
@@ -512,14 +509,7 @@ int hmm_store(ia_css_ptr virt, const void *data, unsigned int bytes)

 		clflush_cache_range(des, len);

-		if (in_atomic())
-			/*
-			 * Note: kunmap_atomic requires return addr from
-			 * kmap_atomic, not the page. See linux/highmem.h
-			 */
-			kunmap_atomic(des - offset);
-		else
-			kunmap(bo->page_obj[idx].page);
+		kunmap_local(des);
 	}

 	return 0;
-- 
2.34.1