add new system file

hc

2024-02-20 102a0743326a03cd1a1202ceda21e175b7d3575c

 kernel/drivers/mailbox/mailbox-test.c
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@@ -12,6 +12,7 @@
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 #include <linux/kernel.h>
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 #include <linux/mailbox_client.h>
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 #include <linux/module.h>
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+#include <linux/mutex.h>
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 #include <linux/of.h>
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 #include <linux/platform_device.h>
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 #include <linux/poll.h>
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@@ -38,6 +39,7 @@
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 	char			*signal;
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 	char			*message;
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 	spinlock_t		lock;
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+	struct mutex		mutex;
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 	wait_queue_head_t	waitq;
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 	struct fasync_struct	*async_queue;
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 	struct dentry		*root_debugfs_dir;
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@@ -95,6 +97,7 @@
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 				       size_t count, loff_t *ppos)
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 {
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 	struct mbox_test_device *tdev = filp->private_data;
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+	char *message;
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 	void *data;
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 	int ret;
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@@ -110,10 +113,13 @@
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 		return -EINVAL;
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 	}
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-	tdev->message = kzalloc(MBOX_MAX_MSG_LEN, GFP_KERNEL);
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-	if (!tdev->message)
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+	message = kzalloc(MBOX_MAX_MSG_LEN, GFP_KERNEL);
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+	if (!message)
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 		return -ENOMEM;
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+	mutex_lock(&tdev->mutex);
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+
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+	tdev->message = message;
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 	ret = copy_from_user(tdev->message, userbuf, count);
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 	if (ret) {
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 		ret = -EFAULT;
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@@ -143,6 +149,8 @@
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 	kfree(tdev->signal);
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 	kfree(tdev->message);
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 	tdev->signal = NULL;
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+
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+	mutex_unlock(&tdev->mutex);
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 	return ret < 0 ? ret : count;
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 }
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@@ -392,6 +400,7 @@
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 	platform_set_drvdata(pdev, tdev);
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 	spin_lock_init(&tdev->lock);
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+	mutex_init(&tdev->mutex);
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 	if (tdev->rx_channel) {
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 		tdev->rx_buffer = devm_kzalloc(&pdev->dev,