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@suse.cz>
Link: https://lore.kernel.org/r/20220124071430.14907-4-jslaby@suse.cz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 7709ce6..7644834 100644 (file)
--- 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 d3ea9ed..58e9619 100644 (file)
--- 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;