linux-kernel - [PATCH 03/11] tty: add kfifo to tty

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Date:   Mon, 24 Jan 2022 08:14:22 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     gregkh@...uxfoundation.org
Cc:     linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        johan@...nel.org, Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 03/11] tty: add kfifo to tty_port

Define a kfifo inside struct tty_port. We use DECLARE_KFIFO_PTR and let
the preexisting tty_port::xmit_buf be also the buffer for the kfifo.
And handle the initialization/decomissioning along with xmit_buf, i.e.
in tty_port_alloc_xmit_buf() and tty_port_free_xmit_buf(), respectively.

This allows for kfifo use in drivers which opt-in, while others still
may use the old xmit_buf. mxser will be the first user in the next
few patches.

Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/tty/tty_port.c   | 6 +++++-
 include/linux/tty_port.h | 3 +++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 7709ce655f44..7644834640f1 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -225,8 +225,11 @@ int tty_port_alloc_xmit_buf(struct tty_port *port)
 {
 	/* We may sleep in get_zeroed_page() */
 	mutex_lock(&port->buf_mutex);
-	if (port->xmit_buf == NULL)
+	if (port->xmit_buf == NULL) {
 		port->xmit_buf = (unsigned char *)get_zeroed_page(GFP_KERNEL);
+		if (port->xmit_buf)
+			kfifo_init(&port->xmit_fifo, port->xmit_buf, PAGE_SIZE);
+	}
 	mutex_unlock(&port->buf_mutex);
 	if (port->xmit_buf == NULL)
 		return -ENOMEM;
@@ -240,6 +243,7 @@ void tty_port_free_xmit_buf(struct tty_port *port)
 	if (port->xmit_buf != NULL) {
 		free_page((unsigned long)port->xmit_buf);
 		port->xmit_buf = NULL;
+		INIT_KFIFO(port->xmit_fifo);
 	}
 	mutex_unlock(&port->buf_mutex);
 }
diff --git a/include/linux/tty_port.h b/include/linux/tty_port.h
index d3ea9ed0b98e..58e9619116b7 100644
--- a/include/linux/tty_port.h
+++ b/include/linux/tty_port.h
@@ -2,6 +2,7 @@
 #ifndef _LINUX_TTY_PORT_H
 #define _LINUX_TTY_PORT_H
 
+#include <linux/kfifo.h>
 #include <linux/kref.h>
 #include <linux/mutex.h>
 #include <linux/tty_buffer.h>
@@ -67,6 +68,7 @@ extern const struct tty_port_client_operations tty_port_default_client_ops;
  * @mutex: locking, for open, shutdown and other port operations
  * @buf_mutex: @xmit_buf alloc lock
  * @xmit_buf: optional xmit buffer used by some drivers
+ * @xmit_fifo: optional xmit buffer used by some drivers
  * @close_delay: delay in jiffies to wait when closing the port
  * @closing_wait: delay in jiffies for output to be sent before closing
  * @drain_delay: set to zero if no pure time based drain is needed else set to
@@ -110,6 +112,7 @@ struct tty_port {
 	struct mutex		mutex;
 	struct mutex		buf_mutex;
 	unsigned char		*xmit_buf;
+	DECLARE_KFIFO_PTR(xmit_fifo, unsigned char);
 	unsigned int		close_delay;
 	unsigned int		closing_wait;
 	int			drain_delay;
-- 
2.34.1