Message-ID: <71837e7a-b0cf-a8ff-788f-50ba68313621@linux.intel.com>
Date: Mon, 6 May 2024 20:03:16 +0300 (EEST)
From: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
To: Christoph Fritz <christoph.fritz@...dev.de>
cc: Jiri Slaby <jirislaby@...nel.org>, 
    Oliver Hartkopp <socketcan@...tkopp.net>, 
    Marc Kleine-Budde <mkl@...gutronix.de>, 
    Vincent Mailhol <mailhol.vincent@...adoo.fr>, 
    "David S . Miller" <davem@...emloft.net>, 
    Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
    Paolo Abeni <pabeni@...hat.com>, Rob Herring <robh@...nel.org>, 
    Krzysztof Kozlowski <krzk+dt@...nel.org>, 
    Conor Dooley <conor+dt@...nel.org>, Jiri Kosina <jikos@...nel.org>, 
    Benjamin Tissoires <bentiss@...nel.org>, 
    Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
    Sebastian Reichel <sre@...nel.org>, 
    Linus Walleij <linus.walleij@...aro.org>, 
    Andreas Lauser <andreas.lauser@...cedes-benz.com>, 
    Jonathan Corbet <corbet@....net>, Pavel Pisa <pisa@....felk.cvut.cz>, 
    linux-can@...r.kernel.org, netdev@...r.kernel.org, 
    devicetree@...r.kernel.org, linux-input@...r.kernel.org, 
    linux-serial@...r.kernel.org
Subject: Re: [PATCH v3 07/11] can: Add support for serdev LIN adapters

On Thu, 2 May 2024, Christoph Fritz wrote:

> This commit introduces LIN-Bus support for UART devices equipped with
> LIN transceivers, utilizing the Serial Device Bus (serdev) interface.
> 
> For more details on an adapter, visit: https://hexdev.de/hexlin#tty
> 
> Signed-off-by: Christoph Fritz <christoph.fritz@...dev.de>
> ---
>  drivers/net/can/Kconfig      |  16 ++
>  drivers/net/can/Makefile     |   1 +
>  drivers/net/can/lin-serdev.c | 500 +++++++++++++++++++++++++++++++++++
>  3 files changed, 517 insertions(+)
>  create mode 100644 drivers/net/can/lin-serdev.c
> 
> diff --git a/drivers/net/can/Kconfig b/drivers/net/can/Kconfig
> index 0934bbf8d03b2..91c6cdeefe440 100644
> --- a/drivers/net/can/Kconfig
> +++ b/drivers/net/can/Kconfig
> @@ -181,6 +181,22 @@ config CAN_LIN
>  
>  	  Actual device drivers need to be enabled too.
>  
> +config CAN_LIN_SERDEV
> +	tristate "Serial LIN Adaptors"
> +	depends on CAN_LIN && SERIAL_DEV_BUS && OF
> +	help
> +	  LIN-Bus support for serial devices equipped with LIN transceievers.
> +	  This device driver is using CAN_LIN for a userland connection on
> +	  one side and the kernel its serial device bus (serdev) interface
> +	  on the other side.
> +
> +	  If you have a hexlin tty adapter, say Y here and see
> +	  <https://hexdev.de/hexlin#tty>.
> +
> +	  This driver can also be built as a module. If so, the module will be
> +	  called lin-serdev.ko.
> +
> +
>  config CAN_SLCAN
>  	tristate "Serial / USB serial CAN Adaptors (slcan)"
>  	depends on TTY
> diff --git a/drivers/net/can/Makefile b/drivers/net/can/Makefile
> index 0093ee9219ca8..21ca514a42439 100644
> --- a/drivers/net/can/Makefile
> +++ b/drivers/net/can/Makefile
> @@ -26,6 +26,7 @@ obj-$(CONFIG_CAN_IFI_CANFD)	+= ifi_canfd/
>  obj-$(CONFIG_CAN_JANZ_ICAN3)	+= janz-ican3.o
>  obj-$(CONFIG_CAN_KVASER_PCIEFD)	+= kvaser_pciefd.o
>  obj-$(CONFIG_CAN_LIN)		+= lin.o
> +obj-$(CONFIG_CAN_LIN_SERDEV)	+= lin-serdev.o
>  obj-$(CONFIG_CAN_MSCAN)		+= mscan/
>  obj-$(CONFIG_CAN_M_CAN)		+= m_can/
>  obj-$(CONFIG_CAN_PEAK_PCIEFD)	+= peak_canfd/
> diff --git a/drivers/net/can/lin-serdev.c b/drivers/net/can/lin-serdev.c
> new file mode 100644
> index 0000000000000..13fd9a54c6c93
> --- /dev/null
> +++ b/drivers/net/can/lin-serdev.c
> @@ -0,0 +1,500 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/* Copyright (C) 2024 hexDEV GmbH - https://hexdev.de */
> +
> +#include <linux/delay.h>
> +#include <linux/init.h>
> +#include <linux/kfifo.h>
> +#include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/serdev.h>
> +#include <linux/slab.h>
> +#include <linux/tty.h>
> +#include <net/lin.h>
> +
> +#define LINSER_SAMPLES_PER_CHAR		10
> +#define LINSER_TX_BUFFER_SIZE		11
> +#define LINSER_RX_FIFO_SIZE		256
> +#define LINSER_PARSE_BUFFER		24
> +
> +struct linser_rx {
> +	u8 data;
> +	u8 flag;
> +};
> +
> +enum linser_rx_status {
> +	NEED_MORE = -1,
> +	MODE_OK = 0,
> +	NEED_FORCE,
> +};
> +
> +struct linser_priv {
> +	struct lin_device *lin_dev;
> +	struct serdev_device *serdev;
> +	DECLARE_KFIFO_PTR(rx_fifo, struct linser_rx);
> +	struct delayed_work rx_work;
> +	unsigned long break_usleep_min;
> +	unsigned long break_usleep_max;
> +	unsigned long post_break_usleep_min;
> +	unsigned long post_break_usleep_max;
> +	unsigned long force_timeout_jfs;
> +	struct lin_responder_answer respond_answ[LIN_NUM_IDS];
> +	struct mutex resp_lock; /* protects respond_answ */
> +	bool is_stopped;
> +};
> +
> +static int linser_open(struct lin_device *ldev)
> +{
> +	struct serdev_device *serdev = to_serdev_device(ldev->dev);
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +	int ret;
> +
> +	if (priv->is_stopped) {
> +		ret = serdev_device_open(serdev);
> +		if (ret) {
> +			dev_err(&serdev->dev, "Unable to open device\n");
> +			return ret;
> +		}
> +
> +		serdev_device_set_flow_control(serdev, false);
> +		serdev_device_set_break_detection(serdev, true);
> +
> +		priv->is_stopped = false;
> +	}
> +
> +	return 0;
> +}
> +
> +static int linser_stop(struct lin_device *ldev)
> +{
> +	struct serdev_device *serdev = to_serdev_device(ldev->dev);
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +
> +	if (priv->is_stopped)
> +		return 0;
> +
> +	serdev_device_close(serdev);
> +	priv->is_stopped = true;
> +
> +	return 0;
> +}
> +
> +static int linser_send_break(struct linser_priv *priv)
> +{
> +	struct serdev_device *serdev = priv->serdev;
> +	int ret;
> +
> +	ret = serdev_device_break_ctl(serdev, -1);
> +	if (ret)
> +		return ret;
> +
> +	usleep_range(priv->break_usleep_min, priv->break_usleep_max);
> +
> +	ret = serdev_device_break_ctl(serdev, 0);
> +	if (ret)
> +		return ret;
> +
> +	usleep_range(priv->post_break_usleep_min, priv->post_break_usleep_max);
> +
> +	return 0;
> +}
> +
> +static int linser_ldo_tx(struct lin_device *ldev, const struct lin_frame *lf)
> +{
> +	struct serdev_device *serdev = to_serdev_device(ldev->dev);
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +	u8 pid = LIN_FORM_PID(lf->lin_id);
> +	u8 buf[LINSER_TX_BUFFER_SIZE];
> +	ssize_t written_len, total_len;
> +	u8 checksum;
> +	int ret;
> +
> +	if (lf->len + 3 > LINSER_TX_BUFFER_SIZE) {
> +		dev_err(&serdev->dev, "Frame length %u exceeds buffer size\n", lf->len);
> +		return -EINVAL;
> +	}
> +
> +	buf[0] = LIN_SYNC_BYTE;
> +	buf[1] = pid;
> +	total_len = 2;
> +
> +	if (lf->len) {
> +		memcpy(&buf[2], lf->data, lf->len);
> +		checksum = lin_get_checksum(pid, lf->len, lf->data,
> +					    lf->checksum_mode);
> +		buf[lf->len + 2] = checksum;
> +		total_len += lf->len + 1;
> +	}
> +
> +	ret = linser_send_break(priv);
> +	if (ret)
> +		return ret;
> +
> +	written_len = serdev_device_write(serdev, buf, total_len, 0);
> +	if (written_len < total_len)
> +		return written_len < 0 ? (int)written_len : -EIO;
> +
> +	dev_dbg(&serdev->dev, "sent out: %*ph\n", (int)total_len, buf);
> +
> +	serdev_device_wait_until_sent(serdev, 0);
> +
> +	return 0;
> +}
> +
> +static void linser_derive_timings(struct linser_priv *priv, u16 bitrate)
> +{
> +	unsigned long break_baud = (bitrate * 2) / 3;
> +	unsigned long timeout_us;
> +
> +	priv->break_usleep_min = (USEC_PER_SEC * LINSER_SAMPLES_PER_CHAR) /
> +				 break_baud;
> +	priv->break_usleep_max = priv->break_usleep_min + 50;
> +	priv->post_break_usleep_min = (USEC_PER_SEC * 1 /* 1 bit */) / break_baud;

Don't mix comments and code like this.

> +	priv->post_break_usleep_max = priv->post_break_usleep_min + 30;
> +
> +	timeout_us = DIV_ROUND_CLOSEST(USEC_PER_SEC * 256 /* bit */, bitrate);

Ditto.

> +	priv->force_timeout_jfs = usecs_to_jiffies(timeout_us);
> +}
> +
> +static int linser_update_bitrate(struct lin_device *ldev, u16 bitrate)
> +{
> +	struct serdev_device *serdev = to_serdev_device(ldev->dev);
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +	unsigned int speed;
> +	int ret;
> +
> +	ret = linser_open(ldev);
> +	if (ret)
> +		return ret;
> +
> +	speed = serdev_device_set_baudrate(serdev, bitrate);
> +	if (!bitrate || speed != bitrate)
> +		return -EINVAL;
> +
> +	linser_derive_timings(priv, bitrate);
> +
> +	return 0;
> +}
> +
> +static int linser_get_responder_answer(struct lin_device *ldev, u8 id,
> +				       struct lin_responder_answer *answ)
> +{
> +	struct serdev_device *serdev = to_serdev_device(ldev->dev);
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +	struct lin_responder_answer *r = &priv->respond_answ[id];
> +
> +	if (!answ)
> +		return -EINVAL;
> +
> +	mutex_lock(&priv->resp_lock);

guard(mutex)(&priv->resp_lock);

> +	memcpy(answ, r, sizeof(struct lin_responder_answer));

sizeof(*answ);

> +	mutex_unlock(&priv->resp_lock);
> +
> +	return 0;
> +}
> +
> +static int linser_update_resp_answer(struct lin_device *ldev,
> +				     const struct lin_responder_answer *answ)
> +{
> +	struct serdev_device *serdev = to_serdev_device(ldev->dev);
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +	struct lin_responder_answer *r = &priv->respond_answ[answ->lf.lin_id];
> +
> +	if (!answ)
> +		return -EINVAL;
> +
> +	mutex_lock(&priv->resp_lock);
> +	memcpy(r, answ, sizeof(struct lin_responder_answer));

Ditto.

> +	r->lf.checksum = lin_get_checksum(LIN_FORM_PID(answ->lf.lin_id),
> +					  answ->lf.len,
> +					  answ->lf.data,
> +					  answ->lf.checksum_mode);
> +	mutex_unlock(&priv->resp_lock);
> +
> +	return 0;
> +}
> +
> +static struct lin_device_ops linser_lindev_ops = {
> +	.ldo_open = linser_open,
> +	.ldo_stop = linser_stop,
> +	.ldo_tx = linser_ldo_tx,
> +	.update_bitrate = linser_update_bitrate,
> +	.get_responder_answer = linser_get_responder_answer,
> +	.update_responder_answer = linser_update_resp_answer,
> +};
> +
> +static bool linser_tx_frame_as_responder(struct linser_priv *priv, u8 id)
> +{
> +	struct lin_responder_answer *answ = &priv->respond_answ[id];
> +	struct serdev_device *serdev = priv->serdev;
> +	u8 buf[LINSER_TX_BUFFER_SIZE];
> +	u8 checksum, count, n;
> +	ssize_t write_len;
> +
> +	mutex_lock(&priv->resp_lock);

scoped_guard() can be used here.

> +
> +	if (!answ->is_active) {
> +		mutex_unlock(&priv->resp_lock);
> +		return false;
> +	}
> +
> +	if (answ->is_event_frame) {
> +		struct lin_responder_answer *e_answ;
> +
> +		e_answ = &priv->respond_answ[answ->event_associated_id];
> +		n = min(e_answ->lf.len, LIN_MAX_DLEN);
> +		if (memcmp(answ->lf.data, e_answ->lf.data, n) != 0) {
> +			memcpy(answ->lf.data, e_answ->lf.data, n);
> +			checksum = lin_get_checksum(LIN_FORM_PID(answ->lf.lin_id),
> +						    n, e_answ->lf.data,
> +						    answ->lf.checksum_mode);
> +			answ = e_answ;
> +		} else {
> +			mutex_unlock(&priv->resp_lock);
> +			return false;

Use reverse logic so you can reduce indent.

> +		}
> +	} else {
> +		checksum = answ->lf.checksum;
> +	}
> +
> +	count = min(answ->lf.len, LIN_MAX_DLEN);
> +	memcpy(&buf[0], answ->lf.data, count);
> +	buf[count] = checksum;
> +
> +	mutex_unlock(&priv->resp_lock);
> +
> +	write_len = serdev_device_write(serdev, buf, count + 1, 0);
> +	if (write_len < count + 1)
> +		return false;
> +
> +	serdev_device_wait_until_sent(serdev, 0);
> +
> +	return true;
> +}
> +
> +static void linser_pop_fifo(struct linser_priv *priv, size_t n)
> +{
> +	for (size_t i = 0; i < n; i++)
> +		kfifo_skip(&priv->rx_fifo);
> +}
> +
> +static int linser_fill_frame(struct linser_priv *priv, struct lin_frame *lf)
> +{
> +	struct serdev_device *serdev = priv->serdev;
> +	struct linser_rx buf[LINSER_PARSE_BUFFER];
> +	unsigned int count, i, brk = 0;
> +
> +	count = kfifo_out_peek(&priv->rx_fifo, buf, LINSER_PARSE_BUFFER);
> +
> +	memset(lf, 0, sizeof(struct lin_frame));
> +
> +	for (i = 0; i < count; i++) {
> +		dev_dbg(&serdev->dev, "buf[%d]: data=%02x, flag=%02x\n",
> +			i, buf[i].data, buf[i].flag);
> +	}
> +
> +	if (count < 3)
> +		return NEED_MORE;
> +
> +	if (buf[0].flag != TTY_BREAK || buf[1].data != LIN_SYNC_BYTE) {
> +		linser_pop_fifo(priv, 1); /* pop incorrect start */
> +		return NEED_MORE;
> +	} else if (!LIN_CHECK_PID(buf[2].data)) {
> +		linser_pop_fifo(priv, 3); /* pop incorrect header */
> +		return NEED_MORE;
> +	}
> +
> +	lf->lin_id = LIN_GET_ID(buf[2].data);
> +
> +	/* from here on we do have a correct LIN header */
> +
> +	if (count == 3)
> +		return linser_tx_frame_as_responder(priv, lf->lin_id) ?
> +		       NEED_MORE : NEED_FORCE;
> +
> +	for (i = 3; i < count && i < LINSER_PARSE_BUFFER && i < 12; i++) {
> +		if (buf[i].flag == TTY_BREAK) {
> +			brk = i;
> +			break;
> +		}
> +		lf->len++;
> +	}
> +	if (lf->len)
> +		lf->len -= 1; /* account for checksum */
> +
> +	if (brk == 3)
> +		return MODE_OK;
> +
> +	if (brk == 4) {
> +		/* suppress wrong answer data-byte in between PID and break
> +		 * because checksum is missing
> +		 */
> +		return MODE_OK;
> +	}
> +
> +	for (i = 0; i < lf->len; i++)
> +		lf->data[i] = buf[3 + i].data;
> +	lf->checksum = buf[2 + lf->len + 1].data;
> +	mutex_lock(&priv->resp_lock);
> +	lf->checksum_mode = priv->respond_answ[lf->lin_id].lf.checksum_mode;
> +	mutex_unlock(&priv->resp_lock);
> +
> +	dev_dbg(&serdev->dev, "brk:%i, len:%u, data:%*ph, checksum:%x (%s)\n",
> +		brk, lf->len, lf->len, lf->data, lf->checksum,
> +		lf->checksum_mode ? "enhanced" : "classic");
> +
> +	if (brk > 4)
> +		return MODE_OK;	/* frame in between two breaks: so complete */
> +
> +	if (lf->len == 8)
> +		return MODE_OK;
> +
> +	return NEED_FORCE;
> +}
> +
> +static int linser_process_frame(struct linser_priv *priv, bool force)
> +{
> +	struct serdev_device *serdev = priv->serdev;
> +	struct lin_frame lf;
> +	size_t bytes_to_pop;
> +	int ret = NEED_MORE;
> +
> +	while (kfifo_len(&priv->rx_fifo) >= LIN_HEADER_SIZE) {
> +		ret = linser_fill_frame(priv, &lf);
> +
> +		if (ret == MODE_OK || (ret == NEED_FORCE && force)) {
> +			dev_dbg(&serdev->dev, "lin_rx: %s\n",
> +				force ? "force" : "normal");
> +			lin_rx(priv->lin_dev, &lf);
> +			bytes_to_pop = LIN_HEADER_SIZE + lf.len +
> +				       (lf.len ? 1 : 0);
> +			linser_pop_fifo(priv, bytes_to_pop);
> +			force = false;
> +			ret = MODE_OK;
> +		} else {
> +			return ret;

Reverse logic & deindent the main block.

> +		}
> +	}
> +
> +	return ret;
> +}
> +
> +static void linser_process_delayed(struct work_struct *work)
> +{
> +	struct linser_priv *priv = container_of(work, struct linser_priv,
> +						rx_work.work);
> +
> +	linser_process_frame(priv, true);
> +}
> +
> +static ssize_t linser_receive_buf_fp(struct serdev_device *serdev,
> +				     const u8 *data, const u8 *fp,
> +				     size_t count)
> +{
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +	enum linser_rx_status rx_status;
> +	ssize_t n = 0;
> +	int i;
> +
> +	cancel_delayed_work_sync(&priv->rx_work);
> +
> +	for (i = 0; i < count; i++) {
> +		struct linser_rx rx;
> +
> +		rx.data = data[i];
> +		rx.flag = (fp ? fp[i] : 0);
> +		n += kfifo_in(&priv->rx_fifo, &rx, 1);
> +		dev_dbg(&serdev->dev, "%s: n:%zd, flag:0x%02x, data:0x%02x\n",
> +			__func__, n, rx.flag, data[i]);
> +	}
> +
> +	rx_status = linser_process_frame(priv, false);
> +
> +	if (rx_status == NEED_FORCE)
> +		schedule_delayed_work(&priv->rx_work, priv->force_timeout_jfs);
> +
> +	return n;
> +}
> +
> +static const struct serdev_device_ops linser_ops = {
> +	.receive_buf_fp = linser_receive_buf_fp,
> +	.write_wakeup = serdev_device_write_wakeup,
> +};
> +
> +static int linser_probe(struct serdev_device *serdev)
> +{
> +	struct linser_priv *priv;
> +	int ret;
> +
> +	priv = devm_kzalloc(&serdev->dev, sizeof(*priv), GFP_KERNEL);
> +	if (!priv)
> +		return -ENOMEM;
> +
> +	ret = kfifo_alloc(&priv->rx_fifo, LINSER_RX_FIFO_SIZE, GFP_KERNEL);
> +	if (ret)
> +		return ret;
> +
> +	INIT_DELAYED_WORK(&priv->rx_work, linser_process_delayed);
> +
> +	priv->serdev = serdev;
> +	serdev_device_set_drvdata(serdev, priv);
> +	serdev_device_set_client_ops(serdev, &linser_ops);
> +
> +	ret = serdev_device_open(serdev);
> +	if (ret) {
> +		dev_err(&serdev->dev, "Unable to open device\n");
> +		goto err_open;
> +	}
> +
> +	serdev_device_set_flow_control(serdev, false);
> +	serdev_device_set_break_detection(serdev, true);
> +	linser_derive_timings(priv, LIN_DEFAULT_BAUDRATE);
> +
> +	mutex_init(&priv->resp_lock);
> +
> +	priv->lin_dev = register_lin(&serdev->dev, &linser_lindev_ops);
> +	if (IS_ERR_OR_NULL(priv->lin_dev)) {
> +		ret = PTR_ERR(priv->lin_dev);
> +		goto err_register_lin;
> +	}
> +
> +	serdev_device_close(serdev);
> +	priv->is_stopped = true;
> +
> +	return 0;
> +
> +err_register_lin:
> +	serdev_device_close(serdev);
> +err_open:
> +	kfifo_free(&priv->rx_fifo);
> +	return ret;
> +}
> +
> +static void linser_remove(struct serdev_device *serdev)
> +{
> +	struct linser_priv *priv = serdev_device_get_drvdata(serdev);
> +
> +	unregister_lin(priv->lin_dev);
> +}
> +
> +static const struct of_device_id linser_of_match[] = {
> +	{
> +		.compatible = "hexdev,lin-serdev",
> +	},
> +	{}
> +};
> +MODULE_DEVICE_TABLE(of, linser_of_match);
> +
> +static struct serdev_device_driver linser_driver = {
> +	.probe = linser_probe,
> +	.remove = linser_remove,
> +	.driver = {
> +		.name = KBUILD_MODNAME,
> +		.of_match_table = linser_of_match,
> +	}
> +};
> +
> +module_serdev_device_driver(linser_driver);
> +
> +MODULE_LICENSE("GPL");
> +MODULE_AUTHOR("Christoph Fritz <christoph.fritz@...dev.de>");
> +MODULE_DESCRIPTION("LIN-Bus serdev driver");
> 

-- 
 i.

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