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Subject[PATCH v2] staging: pi433: add comment to rx_lock mutex definition
Checkpatch reports: CHECK: struct mutex definition without comment.
Fix this by documenting what rx_mutex struct is used for in pi433 driver.

Signed-off-by: Paulo Miguel Almeida <paulo.miguel.almeida.rodenas@gmail.com>
---
v2: ellaborate on reasons why the mutex lock is used in the driver (Req: Greg k-h)
v1: https://lore.kernel.org/lkml/20211222093626.GA13332@localhost.localdomain/
---
drivers/staging/pi433/pi433_if.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/drivers/staging/pi433/pi433_if.c b/drivers/staging/pi433/pi433_if.c
index 29bd37669059..1cd3d5f2df2a 100644
--- a/drivers/staging/pi433/pi433_if.c
+++ b/drivers/staging/pi433/pi433_if.c
@@ -92,6 +92,17 @@ struct pi433_device {
u32 rx_bytes_to_drop;
u32 rx_bytes_dropped;
unsigned int rx_position;
+ /*
+ * rx_lock is used to avoid race-conditions that can be triggered from userspace.
+ *
+ * For instance, if a program in userspace is reading the char device
+ * allocated in this module then another program won't be able to change RX
+ * configuration of the RF69 hardware module via ioctl and vice versa.
+ *
+ * utilization summary:
+ * - pi433_read: blocks are read until rx read something (up to the buffer size)
+ * - pi433_ioctl: during pending read request, change of config not allowed
+ */
struct mutex rx_lock;
wait_queue_head_t rx_wait_queue;

--
2.25.4
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