linux-kernel - [PATCH 04/31] staging: wfx: fix comment correctness

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Message-Id: <20220113085524.1110708-5-Jerome.Pouiller@silabs.com>
Date:   Thu, 13 Jan 2022 09:54:57 +0100
From:   Jerome Pouiller <Jerome.Pouiller@...abs.com>
To:     devel@...verdev.osuosl.org, linux-wireless@...r.kernel.org
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Kalle Valo <kvalo@...eaurora.org>,
        "David S . Miller" <davem@...emloft.net>,
        Jérôme Pouiller 
        <jerome.pouiller@...abs.com>
Subject: [PATCH 04/31] staging: wfx: fix comment correctness

From: Jérôme Pouiller <jerome.pouiller@...abs.com>

Using DMA with stack allocated buffers is not supported, whatever the
value of CONFIG_VMAP_STACK.

Signed-off-by: Jérôme Pouiller <jerome.pouiller@...abs.com>
---
 drivers/staging/wfx/hwio.c | 12 ------------
 drivers/staging/wfx/hwio.h |  4 ++++
 2 files changed, 4 insertions(+), 12 deletions(-)

diff --git a/drivers/staging/wfx/hwio.c b/drivers/staging/wfx/hwio.c
index 30eb888830d2..393bcb1e2f4e 100644
--- a/drivers/staging/wfx/hwio.c
+++ b/drivers/staging/wfx/hwio.c
@@ -14,18 +14,6 @@
 #include "bus.h"
 #include "traces.h"
 
-/*
- * Internal helpers.
- *
- * About CONFIG_VMAP_STACK:
- * When CONFIG_VMAP_STACK is enabled, it is not possible to run DMA on stack
- * allocated data. Functions below that work with registers (aka functions
- * ending with "32") automatically reallocate buffers with kmalloc. However,
- * functions that work with arbitrary length buffers let's caller to handle
- * memory location. In doubt, enable CONFIG_DEBUG_SG to detect badly located
- * buffer.
- */
-
 static int read32(struct wfx_dev *wdev, int reg, u32 *val)
 {
 	int ret;
diff --git a/drivers/staging/wfx/hwio.h b/drivers/staging/wfx/hwio.h
index ff09575dd1af..d34baae47017 100644
--- a/drivers/staging/wfx/hwio.h
+++ b/drivers/staging/wfx/hwio.h
@@ -12,6 +12,10 @@
 
 struct wfx_dev;
 
+/* Caution: in the functions below, 'buf' will used with a DMA. So, it must be
+ * kmalloc'd (do not use stack allocated buffers). In doubt, enable
+ * CONFIG_DEBUG_SG to detect badly located buffer.
+ */
 int wfx_data_read(struct wfx_dev *wdev, void *buf, size_t buf_len);
 int wfx_data_write(struct wfx_dev *wdev, const void *buf, size_t buf_len);
 
-- 
2.34.1