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SubjectRe: [PATCH v8 2/2] tty: add rpmsg driver
On Thu, Sep 30, 2021 at 06:05:20PM +0200, Arnaud Pouliquen wrote:
> This driver exposes a standard TTY interface on top of the rpmsg
> framework through a rpmsg service.
>
> This driver supports multi-instances, offering a /dev/ttyRPMSGx entry
> per rpmsg endpoint.
>
> Signed-off-by: Arnaud Pouliquen <arnaud.pouliquen@foss.st.com>
> ---
> Documentation/serial/tty_rpmsg.rst | 15 ++
> drivers/tty/Kconfig | 9 +
> drivers/tty/Makefile | 1 +
> drivers/tty/rpmsg_tty.c | 275 +++++++++++++++++++++++++++++
> 4 files changed, 300 insertions(+)
> create mode 100644 Documentation/serial/tty_rpmsg.rst
> create mode 100644 drivers/tty/rpmsg_tty.c
>
> diff --git a/Documentation/serial/tty_rpmsg.rst b/Documentation/serial/tty_rpmsg.rst
> new file mode 100644
> index 000000000000..b055107866c9
> --- /dev/null
> +++ b/Documentation/serial/tty_rpmsg.rst
> @@ -0,0 +1,15 @@
> +.. SPDX-License-Identifier: GPL-2.0
> +
> +=========
> +RPMsg TTY
> +=========
> +
> +The rpmsg tty driver implements serial communication on the RPMsg bus to makes possible for
> +user-space programs to send and receive rpmsg messages as a standard tty protocol.
> +
> +The remote processor can instantiate a new tty by requesting a "rpmsg-tty" RPMsg service.
> +
> +The "rpmsg-tty" service is directly used for data exchange. No flow control is implemented.
> +
> +Information related to the RPMsg and associated tty device is available in
> +/sys/bus/rpmsg/devices/.


Why is this file needed? Nothing references it, and this would be the
only file in this directory.

> diff --git a/drivers/tty/Kconfig b/drivers/tty/Kconfig
> index 23cc988c68a4..5095513029d7 100644
> --- a/drivers/tty/Kconfig
> +++ b/drivers/tty/Kconfig
> @@ -368,6 +368,15 @@ config VCC
>
> source "drivers/tty/hvc/Kconfig"
>
> +config RPMSG_TTY
> + tristate "RPMSG tty driver"
> + depends on RPMSG
> + help
> + Say y here to export rpmsg endpoints as tty devices, usually found
> + in /dev/ttyRPMSGx.
> + This makes it possible for user-space programs to send and receive
> + rpmsg messages as a standard tty protocol.

What is the module name going to be?


> +
> endif # TTY
>
> source "drivers/tty/serdev/Kconfig"
> diff --git a/drivers/tty/Makefile b/drivers/tty/Makefile
> index a2bd75fbaaa4..07aca5184a55 100644
> --- a/drivers/tty/Makefile
> +++ b/drivers/tty/Makefile
> @@ -26,5 +26,6 @@ obj-$(CONFIG_PPC_EPAPR_HV_BYTECHAN) += ehv_bytechan.o
> obj-$(CONFIG_GOLDFISH_TTY) += goldfish.o
> obj-$(CONFIG_MIPS_EJTAG_FDC_TTY) += mips_ejtag_fdc.o
> obj-$(CONFIG_VCC) += vcc.o
> +obj-$(CONFIG_RPMSG_TTY) += rpmsg_tty.o
>
> obj-y += ipwireless/
> diff --git a/drivers/tty/rpmsg_tty.c b/drivers/tty/rpmsg_tty.c
> new file mode 100644
> index 000000000000..0c99f54c2911
> --- /dev/null
> +++ b/drivers/tty/rpmsg_tty.c
> @@ -0,0 +1,275 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) STMicroelectronics 2021 - All Rights Reserved

Copyright needs a year, right?

> + */
> +
> +#include <linux/module.h>
> +#include <linux/rpmsg.h>
> +#include <linux/slab.h>
> +#include <linux/tty.h>
> +#include <linux/tty_flip.h>
> +
> +#define MAX_TTY_RPMSG 32

Why have a max at all?


> +
> +static DEFINE_IDR(tty_idr); /* tty instance id */
> +static DEFINE_MUTEX(idr_lock); /* protects tty_idr */

I didn't think an idr needed a lock anymore, are you sure this is
needed?


> +
> +static struct tty_driver *rpmsg_tty_driver;
> +
> +struct rpmsg_tty_port {
> + struct tty_port port; /* TTY port data */
> + int id; /* TTY rpmsg index */
> + struct rpmsg_device *rpdev; /* rpmsg device */
> +};
> +
> +static int rpmsg_tty_cb(struct rpmsg_device *rpdev, void *data, int len, void *priv, u32 src)
> +{
> + struct rpmsg_tty_port *cport = dev_get_drvdata(&rpdev->dev);
> + int copied;
> +
> + if (!len)
> + return -EINVAL;

How can len be 0?


> + copied = tty_insert_flip_string(&cport->port, data, len);
> + if (copied != len)
> + dev_dbg(&rpdev->dev, "Trunc buffer: available space is %d\n",
> + copied);

Is this the proper error handling?


> + tty_flip_buffer_push(&cport->port);

Shouldn't you return the number of bytes sent?

> +
> + return 0;
> +}
> +
> +static int rpmsg_tty_install(struct tty_driver *driver, struct tty_struct *tty)
> +{
> + struct rpmsg_tty_port *cport = idr_find(&tty_idr, tty->index);
> +
> + if (!cport) {
> + dev_err(tty->dev, "Cannot get cport\n");

How can this happen?


> + return -ENODEV;
> + }
> +
> + tty->driver_data = cport;
> +
> + return tty_port_install(&cport->port, driver, tty);
> +}
> +
> +static int rpmsg_tty_open(struct tty_struct *tty, struct file *filp)
> +{
> + return tty_port_open(tty->port, tty, filp);
> +}
> +
> +static void rpmsg_tty_close(struct tty_struct *tty, struct file *filp)
> +{
> + return tty_port_close(tty->port, tty, filp);
> +}
> +
> +static int rpmsg_tty_write(struct tty_struct *tty, const u8 *buf, int len)
> +{
> + struct rpmsg_tty_port *cport = tty->driver_data;
> + struct rpmsg_device *rpdev;
> + int msg_max_size, msg_size;
> + int ret;
> +
> + rpdev = cport->rpdev;
> +
> + dev_dbg(&rpdev->dev, "Send msg from tty->index = %d, len = %d\n", tty->index, len);

ftrace is your friend, is this really still needed?

thanks,

greg k-h

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