[PATCH 2/2] rpmsg: add syslog redirection driver

[Xiang Xiao <xiaoxiang781216@gmail.com>]

From: Guiding Li <liguiding@pinecone.net>

This driver allows the remote processor redirect the output of
syslog/printf into the kernel log, which is very useful to see
what happen in the remote side.

Signed-off-by: Guiding Li <liguiding@pinecone.net>
---
 drivers/rpmsg/Kconfig        |  12 ++++
 drivers/rpmsg/Makefile       |   1 +
 drivers/rpmsg/rpmsg_syslog.c | 163 +++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 176 insertions(+)
 create mode 100644 drivers/rpmsg/rpmsg_syslog.c

diff --git a/drivers/rpmsg/Kconfig b/drivers/rpmsg/Kconfig
index d0322b4..d701614 100644
--- a/drivers/rpmsg/Kconfig
+++ b/drivers/rpmsg/Kconfig
@@ -15,6 +15,18 @@ config RPMSG_CHAR
 	  in /dev. They make it possible for user-space programs to send and
 	  receive rpmsg packets.
 
+config RPMSG_SYSLOG
+	tristate "RPMSG syslog redirection"
+	depends on RPMSG
+	help
+	  Say Y here to redirect the syslog/printf from remote processor into
+	  the kernel log which is very useful to see what happen in the remote
+	  side.
+
+	  If the remote processor hang during bootup or panic at the runtime,
+	  We can even cat /sys/kernel/debug/remoteproc/remoteprocX/trace0 to
+	  get the last log which doesn't output yet.
+
 config RPMSG_QCOM_GLINK_NATIVE
 	tristate
 	select RPMSG
diff --git a/drivers/rpmsg/Makefile b/drivers/rpmsg/Makefile
index 9aa8595..bfd22df 100644
--- a/drivers/rpmsg/Makefile
+++ b/drivers/rpmsg/Makefile
@@ -1,6 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 obj-$(CONFIG_RPMSG)		+= rpmsg_core.o
 obj-$(CONFIG_RPMSG_CHAR)	+= rpmsg_char.o
+obj-$(CONFIG_RPMSG_SYSLOG)	+= rpmsg_syslog.o
 obj-$(CONFIG_RPMSG_QCOM_GLINK_RPM) += qcom_glink_rpm.o
 obj-$(CONFIG_RPMSG_QCOM_GLINK_NATIVE) += qcom_glink_native.o
 obj-$(CONFIG_RPMSG_QCOM_GLINK_SMEM) += qcom_glink_smem.o
diff --git a/drivers/rpmsg/rpmsg_syslog.c b/drivers/rpmsg/rpmsg_syslog.c
new file mode 100644
index 0000000..b7a0d27
--- /dev/null
+++ b/drivers/rpmsg/rpmsg_syslog.c
@@ -0,0 +1,163 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2017 Pinecone Inc.
+ *
+ * redirect syslog/printf from remote to the kernel.
+ */
+
+#include <linux/module.h>
+#include <linux/rpmsg.h>
+#include <linux/slab.h>
+
+#define RPMSG_SYSLOG_TRANSFER		0
+#define RPMSG_SYSLOG_TRANSFER_DONE	1
+#define RPMSG_SYSLOG_SUSPEND		2
+#define RPMSG_SYSLOG_RESUME		3
+
+struct rpmsg_syslog_header {
+	u32				command;
+	s32				result;
+} __packed;
+
+struct rpmsg_syslog_transfer {
+	struct rpmsg_syslog_header	header;
+	u32				count;
+	char				data[0];
+} __packed;
+
+#define rpmsg_syslog_suspend		rpmsg_syslog_header
+#define rpmsg_syslog_resume		rpmsg_syslog_header
+#define rpmsg_syslog_transfer_done	rpmsg_syslog_header
+
+struct rpmsg_syslog {
+	char				*buf;
+	unsigned int			next;
+	unsigned int			size;
+};
+
+static int rpmsg_syslog_callback(struct rpmsg_device *rpdev,
+				 void *data, int len, void *priv_, u32 src)
+{
+	struct rpmsg_syslog *priv = dev_get_drvdata(&rpdev->dev);
+	struct rpmsg_syslog_transfer *msg = data;
+	struct rpmsg_syslog_transfer_done done;
+	unsigned int copied = msg->count;
+	unsigned int printed = 0;
+	const char *nl;
+
+	if (msg->header.command != RPMSG_SYSLOG_TRANSFER)
+		return -EINVAL;
+
+	/* output the message before '\n' to the kernel log */
+	nl = memrchr(msg->data, '\n', msg->count);
+	if (nl) {
+		printed = nl + 1 - msg->data;
+		copied = msg->count - printed;
+
+		if (priv->next) {
+			pr_info("%.*s%.*s", priv->next,
+				priv->buf, printed, msg->data);
+			priv->next = 0;
+		} else {
+			pr_info("%.*s", printed, msg->data);
+		}
+	}
+
+	/* append the message after '\n' to the buffer */
+	if (copied != 0) {
+		unsigned int newsize = priv->next + copied;
+
+		if (newsize > priv->size) {
+			char *newbuf;
+
+			newbuf = krealloc(priv->buf, newsize, GFP_KERNEL);
+			if (newbuf) {
+				priv->buf  = newbuf;
+				priv->size = newsize;
+			} else {
+				copied = priv->size - priv->next;
+			}
+		}
+
+		strncpy(priv->buf + priv->next, msg->data + printed, copied);
+		priv->next += copied;
+	}
+
+	done.command = RPMSG_SYSLOG_TRANSFER_DONE;
+	done.result  = printed + copied;
+	return rpmsg_send(rpdev->ept, &done, sizeof(done));
+}
+
+static int rpmsg_syslog_probe(struct rpmsg_device *rpdev)
+{
+	struct rpmsg_syslog *priv;
+
+	priv = devm_kzalloc(&rpdev->dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	dev_set_drvdata(&rpdev->dev, priv);
+	return 0;
+}
+
+static void rpmsg_syslog_remove(struct rpmsg_device *rpdev)
+{
+	struct rpmsg_syslog *priv = dev_get_drvdata(&rpdev->dev);
+
+	/* flush the buffered log if need */
+	if (priv->next)
+		pr_info("%.*s\n", priv->next, priv->buf);
+	kfree(priv->buf);
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int rpmsg_syslog_dev_suspend(struct device *dev)
+{
+	struct rpmsg_device *rpdev = dev_get_drvdata(dev);
+	struct rpmsg_syslog_suspend msg = {
+		.command = RPMSG_SYSLOG_SUSPEND,
+	};
+
+	return rpmsg_send(rpdev->ept, &msg, sizeof(msg));
+}
+
+static int rpmsg_syslog_dev_resume(struct device *dev)
+{
+	struct rpmsg_device *rpdev = dev_get_drvdata(dev);
+	struct rpmsg_syslog_resume msg = {
+		.command = RPMSG_SYSLOG_RESUME,
+	};
+
+	return rpmsg_send(rpdev->ept, &msg, sizeof(msg));
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(rpmsg_syslog_pm,
+			rpmsg_syslog_dev_suspend,
+			rpmsg_syslog_dev_resume);
+
+static const struct rpmsg_device_id rpmsg_syslog_id_table[] = {
+	{ .name = "rpmsg-syslog" },
+	{ },
+};
+MODULE_DEVICE_TABLE(rpmsg, rpmsg_syslog_id_table);
+
+static struct rpmsg_driver rpmsg_syslog_driver = {
+	.drv = {
+		.name  = "rpmsg_syslog",
+		.owner = THIS_MODULE,
+		.pm    = &rpmsg_syslog_pm,
+	},
+
+	.id_table = rpmsg_syslog_id_table,
+	.probe    = rpmsg_syslog_probe,
+	.callback = rpmsg_syslog_callback,
+	.remove   = rpmsg_syslog_remove,
+};
+
+module_rpmsg_driver(rpmsg_syslog_driver);
+
+MODULE_ALIAS("rpmsg:rpmsg_syslog");
+MODULE_AUTHOR("Guiding Li <liguiding@pinecone.net>");
+MODULE_DESCRIPTION("rpmsg syslog redirection driver");
+MODULE_LICENSE("GPL v2");
-- 
2.7.4