Date:   Wed, 25 Mar 2020 09:45:57 +0100
From:   Jiri Slaby <jslaby@...e.cz>
To:     Arnaud Pouliquen <arnaud.pouliquen@...com>,
        Ohad Ben-Cohen <ohad@...ery.com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-remoteproc@...r.kernel.org,
        Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suman Anna <s-anna@...com>,
        Fabien DESSENNE <fabien.dessenne@...com>,
        linux-stm32@...md-mailman.stormreply.com,
        xiang xiao <xiaoxiang781216@...il.com>
Subject: Re: [PATCH v7 2/2] tty: add rpmsg driver

On 24. 03. 20, 18:04, Arnaud Pouliquen wrote:
> --- /dev/null
> +++ b/drivers/tty/rpmsg_tty.c
> @@ -0,0 +1,417 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (C) STMicroelectronics 2020 - All Rights Reserved
> + * Authors: Arnaud Pouliquen <arnaud.pouliquen@...com> for STMicroelectronics.
> + */
...
> +typedef void (*rpmsg_tty_rx_cb_t)(struct rpmsg_device *, void *, int, void *,
> +				  u32);

Unused, it seems?

> +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 (src == cport->data_dst) {
> +		/* data message */
> +		if (!len)
> +			return -EINVAL;
> +		copied = tty_insert_flip_string_fixed_flag(&cport->port, data,
> +							   TTY_NORMAL, len);

Provided you always pass TTY_NORMAL, why not simply call
tty_insert_flip_string instead?

> +		if (copied != len)
> +			dev_dbg(&rpdev->dev, "trunc buffer: available space is %d\n",
> +				copied);
> +		tty_flip_buffer_push(&cport->port);
> +	} else {
> +		/* control message */
> +		struct rpmsg_tty_ctrl *msg = data;
> +
> +		if (len != sizeof(*msg))
> +			return -EINVAL;
> +
> +		cport->data_dst = msg->d_ept_addr;
> +
> +		/* Update remote cts state */
> +		cport->cts = msg->cts ? 1 : 0;

Number to bool implicit conversion needs no magic, just do:
cport->cts = msg->cts;

> +		if (cport->cts)
> +			tty_port_tty_wakeup(&cport->port);
> +	}
> +
> +	return 0;
> +}
> +
> +static void rpmsg_tty_send_term_ready(struct tty_struct *tty, u8 state)

Should the state be bool? Should it be named "ready" instead?

> +{
> +	struct rpmsg_tty_port *cport = tty->driver_data;
> +	struct rpmsg_tty_ctrl m_ctrl;
> +	int ret;
> +
> +	m_ctrl.cts = state;
> +	m_ctrl.d_ept_addr = cport->d_ept->addr;
> +
> +	ret = rpmsg_trysend(cport->cs_ept, &m_ctrl, sizeof(m_ctrl));
> +	if (ret < 0)
> +		dev_dbg(tty->dev, "cannot send control (%d)\n", ret);
> +};
> +
> +static void rpmsg_tty_throttle(struct tty_struct *tty)
> +{
> +	struct rpmsg_tty_port *cport = tty->driver_data;
> +
> +	/* Disable remote transmission */
> +	if (cport->cs_ept)
> +		rpmsg_tty_send_term_ready(tty, 0);

then s/0/false/;

> +};
> +
> +static void rpmsg_tty_unthrottle(struct tty_struct *tty)
> +{
> +	struct rpmsg_tty_port *cport = tty->driver_data;
> +
> +	/* Enable remote transmission */
> +	if (cport->cs_ept)
> +		rpmsg_tty_send_term_ready(tty, 1);

and s/1/true/;

> +};
...
> +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;
> +	u8 *tmpbuf;
> +
> +	/* If cts not set, the message is not sent*/
> +	if (!cport->cts)
> +		return 0;
> +
> +	rpdev = cport->rpdev;
> +
> +	dev_dbg(&rpdev->dev, "%s: send msg from tty->index = %d, len = %d\n",
> +		__func__, tty->index, len);
> +
> +	msg_max_size = rpmsg_get_mtu(rpdev->ept);
> +
> +	msg_size = min(len, msg_max_size);
> +	tmpbuf = kzalloc(msg_size, GFP_KERNEL);
> +	if (!tmpbuf)
> +		return -ENOMEM;
> +
> +	memcpy(tmpbuf, buf, msg_size);

This is kmemdup, but why do you do that in the first place?

> +	/*
> +	 * Try to send the message to remote processor, if failed return 0 as
> +	 * no data sent
> +	 */
> +	ret = rpmsg_trysendto(cport->d_ept, tmpbuf, msg_size, cport->data_dst);

data of rpmsg_trysendto is not const. OK, you seem you need to change
that first, I see no blocker for that.

> +	kfree(tmpbuf);
> +	if (ret) {
> +		dev_dbg(&rpdev->dev, "rpmsg_send failed: %d\n", ret);
> +		return 0;
> +	}
> +
> +	return msg_size;
> +}
> +
> +static int rpmsg_tty_write_room(struct tty_struct *tty)
> +{
> +	struct rpmsg_tty_port *cport = tty->driver_data;
> +
> +	return cport->cts ? rpmsg_get_mtu(cport->rpdev->ept) : 0;

With if, this would be more readable, IMO.

> +}
...> +static struct rpmsg_tty_port *rpmsg_tty_alloc_cport(void)
> +{
> +	struct rpmsg_tty_port *cport;
> +
> +	cport = kzalloc(sizeof(*cport), GFP_KERNEL);
> +	if (!cport)
> +		return ERR_PTR(-ENOMEM);
> +
> +	mutex_lock(&idr_lock);
> +	cport->id = idr_alloc(&tty_idr, cport, 0, MAX_TTY_RPMSG, GFP_KERNEL);
> +	mutex_unlock(&idr_lock);
> +
> +	if (cport->id < 0) {
> +		kfree(cport);
> +		return ERR_PTR(-ENOSPC);

You should return ERR_PTR(cport->id) instead. It might be ENOMEM too.

> +	}
> +
> +	return cport;
> +}
...
> +static int rpmsg_tty_port_activate(struct tty_port *p, struct tty_struct *tty)
> +{
> +	p->low_latency = (p->flags & ASYNC_LOW_LATENCY) ? 1 : 0;
> +
> +	/* Allocate the buffer we use for writing data */

Where exactly -- am I missing something?

> +	return tty_port_alloc_xmit_buf(p);
> +}
> +
> +static void rpmsg_tty_port_shutdown(struct tty_port *p)
> +{
> +	/* Free the write buffer */
> +	tty_port_free_xmit_buf(p);
> +}
...
> +static int rpmsg_tty_probe(struct rpmsg_device *rpdev)
> +{
> +	struct rpmsg_tty_port *cport;
> +	struct device *dev = &rpdev->dev;
> +	struct rpmsg_channel_info chinfo;
> +	struct device *tty_dev;
> +	int ret;
> +
> +	cport = rpmsg_tty_alloc_cport();
> +	if (IS_ERR(cport)) {
> +		dev_err(dev, "failed to alloc tty port\n");
> +		return PTR_ERR(cport);
> +	}
> +
> +	if (!strncmp(rpdev->id.name, TTY_CH_NAME_WITH_CTS,
> +		     sizeof(TTY_CH_NAME_WITH_CTS))) {

sizeof of a string feels unnatural, but will work in this case. Can a
compiler optimize strlen of a static string?

> +		/*
> +		 * the default endpoint is used for control. Create a second
> +		 * endpoint for the data that would be exchanges trough control
> +		 * endpoint. address of the data endpoint will be provided with
> +		 * the cts state
> +		 */
> +		cport->cs_ept = rpdev->ept;
> +		cport->data_dst = RPMSG_ADDR_ANY;
> +
> +		strscpy(chinfo.name, TTY_CH_NAME_WITH_CTS, sizeof(chinfo.name));
> +		chinfo.src = RPMSG_ADDR_ANY;
> +		chinfo.dst = RPMSG_ADDR_ANY;
> +
> +		cport->d_ept = rpmsg_create_ept(rpdev, rpmsg_tty_cb, cport,
> +						chinfo);
> +		if (!cport->d_ept) {
> +			dev_err(dev, "failed to create tty control channel\n");
> +			ret = -ENOMEM;
> +			goto err_r_cport;
> +		}
> +		dev_dbg(dev, "%s: creating data endpoint with address %#x\n",
> +			__func__, cport->d_ept->addr);
> +	} else {
> +		/*
> +		 * TTY over rpmsg without CTS management the default endpoint
> +		 * is use for raw data transmission.
> +		 */
> +		cport->cs_ept = NULL;
> +		cport->cts = 1;
> +		cport->d_ept = rpdev->ept;
> +		cport->data_dst = rpdev->dst;
> +	}
> +
> +	tty_port_init(&cport->port);
> +	cport->port.ops = &rpmsg_tty_port_ops;

I expected these two in rpmsg_tty_alloc_cport.

> +
> +	tty_dev = tty_port_register_device(&cport->port, rpmsg_tty_driver,
> +					   cport->id, dev);
> +	if (IS_ERR(tty_dev)) {
> +		dev_err(dev, "failed to register tty port\n");
> +		ret = PTR_ERR(tty_dev);
> +		goto  err_destroy;
> +	}
> +
> +	cport->rpdev = rpdev;
> +
> +	dev_set_drvdata(dev, cport);
> +
> +	dev_dbg(dev, "new channel: 0x%x -> 0x%x : ttyRPMSG%d\n",
> +		rpdev->src, rpdev->dst, cport->id);
> +
> +	return 0;
> +
> +err_destroy:
> +	tty_port_destroy(&cport->port);
> +	if (cport->cs_ept)
> +		rpmsg_destroy_ept(cport->d_ept);
> +err_r_cport:
> +	rpmsg_tty_release_cport(cport);
> +
> +	return ret;
> +}

thanks,
-- 
js
suse labs

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