linux-kernel - [PATCH] staging: vme_user: vme_bridge.h: Document mutex in vme_dma

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Message-Id: <20240803001814.7752-1-riyandhiman14@gmail.com>
Date: Sat,  3 Aug 2024 05:48:14 +0530
From: Riyan Dhiman <riyandhiman14@...il.com>
To: gregkh@...uxfoundation.org
Cc: dri-devel@...ts.freedesktop.org,
	linux-fbdev@...r.kernel.org,
	linux-staging@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Riyan Dhiman <riyandhiman14@...il.com>
Subject: [PATCH] staging: vme_user: vme_bridge.h: Document mutex in vme_dma_resource structure

Adhere to Linux kernel coding style

Reported by checkpatch:

CHECK: mutex definition without comment

Proof for comment:

1. The mutex is used to protect access to the 'running' list
(line 1798 tsi148_dma_list_exec function)
	mutex_lock(&ctrlrl->mtx);
	if (!list_empty(&ctrlr->running)) {
		mutex_unlock(&ctrlr->mtx);
		return -EBUSY;
	}
  This prevents race conditions when multiple threads attempt to start DMA
  operations simultaneously.

2. It's also used when removing DMA list from running list:
(line 1862 tsi148_dma_list_exec function)
	mutex_lock(&ctrlr->mtx);
	list_del(&list->list);
	mutex_unlock(&ctrlr->mtx);
  Ensuring thread-safe modification of the controller's state.

Without this mutex, concurrent access to the DMA controller's state could
lead to data corruption or inconsistant state.

Signed-off-by: Riyan Dhiman <riyandhiman14@...il.com>
---
 drivers/staging/vme_user/vme_bridge.h | 1 +
 1 file changed, 1 insertion(+)

diff --git a/drivers/staging/vme_user/vme_bridge.h b/drivers/staging/vme_user/vme_bridge.h
index 9bdc41bb6602..bb3750b40eb1 100644
--- a/drivers/staging/vme_user/vme_bridge.h
+++ b/drivers/staging/vme_user/vme_bridge.h
@@ -61,6 +61,7 @@ struct vme_dma_list {
 struct vme_dma_resource {
 	struct list_head list;
 	struct vme_bridge *parent;
+	/* Mutex to protect DMA controller resources and ensure thread-safe operations */
 	struct mutex mtx;
 	int locked;
 	int number;
-- 
2.39.2