Message-ID: <909777a0-a70e-2174-4455-4afa0591a462@microchip.com>
Date:   Thu, 22 Aug 2019 10:09:09 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <poeschel@...onage.de>, <gregkh@...uxfoundation.org>,
        <tglx@...utronix.de>, <swinslow@...il.com>, <allison@...utok.net>,
        <opensource@...ayne.com>, <kstewart@...uxfoundation.org>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>
CC:     <johan@...nel.org>
Subject: Re: [PATCH v6 5/7] nfc: pn533: add UART phy driver

Hi Lars,

On 20.08.2019 15:03, Lars Poeschel wrote:
> This adds the UART phy interface for the pn533 driver.
> The pn533 driver can be used through UART interface this way.
> It is implemented as a serdev device.
> 
> Cc: Johan Hovold <johan@...nel.org>
> Signed-off-by: Lars Poeschel <poeschel@...onage.de>
> ---
> Changes in v6:
> - Rebased the patch series on v5.3-rc5
> 
> Changes in v5:
> - Use the splitted pn53x_common_init and pn53x_register_nfc
>   and pn53x_common_clean and pn53x_unregister_nfc alike
> 
> Changes in v4:
> - SPDX-License-Identifier: GPL-2.0+
> - Source code comments above refering items
> - Error check for serdev_device_write's
> - Change if (xxx == NULL) to if (!xxx)
> - Remove device name from a dev_err
> - move pn533_register in _probe a bit towards the end of _probe
> - make use of newly added dev_up / dev_down phy_ops
> - control send_wakeup variable from dev_up / dev_down
> 
> Changes in v3:
> - depend on SERIAL_DEV_BUS in Kconfig
> 
> Changes in v2:
> - switched from tty line discipline to serdev, resulting in many
>   simplifications
> - SPDX License Identifier
> 
>  drivers/nfc/pn533/Kconfig  |  11 ++
>  drivers/nfc/pn533/Makefile |   2 +
>  drivers/nfc/pn533/pn533.h  |   8 +
>  drivers/nfc/pn533/uart.c   | 316 +++++++++++++++++++++++++++++++++++++
>  4 files changed, 337 insertions(+)
>  create mode 100644 drivers/nfc/pn533/uart.c
> 
> diff --git a/drivers/nfc/pn533/Kconfig b/drivers/nfc/pn533/Kconfig
> index f6d6b345ba0d..7fe1bbe26568 100644
> --- a/drivers/nfc/pn533/Kconfig
> +++ b/drivers/nfc/pn533/Kconfig
> @@ -26,3 +26,14 @@ config NFC_PN533_I2C
>  
>  	  If you choose to build a module, it'll be called pn533_i2c.
>  	  Say N if unsure.
> +
> +config NFC_PN532_UART
> +	tristate "NFC PN532 device support (UART)"
> +	depends on SERIAL_DEV_BUS
> +	select NFC_PN533
> +	---help---
> +	  This module adds support for the NXP pn532 UART interface.
> +	  Select this if your platform is using the UART bus.
> +
> +	  If you choose to build a module, it'll be called pn532_uart.
> +	  Say N if unsure.
> diff --git a/drivers/nfc/pn533/Makefile b/drivers/nfc/pn533/Makefile
> index 43c25b4f9466..b9648337576f 100644
> --- a/drivers/nfc/pn533/Makefile
> +++ b/drivers/nfc/pn533/Makefile
> @@ -4,7 +4,9 @@
>  #
>  pn533_usb-objs  = usb.o
>  pn533_i2c-objs  = i2c.o
> +pn532_uart-objs  = uart.o
>  
>  obj-$(CONFIG_NFC_PN533)     += pn533.o
>  obj-$(CONFIG_NFC_PN533_USB) += pn533_usb.o
>  obj-$(CONFIG_NFC_PN533_I2C) += pn533_i2c.o
> +obj-$(CONFIG_NFC_PN532_UART) += pn532_uart.o
> diff --git a/drivers/nfc/pn533/pn533.h b/drivers/nfc/pn533/pn533.h
> index 510ddebbd896..6541088fad73 100644
> --- a/drivers/nfc/pn533/pn533.h
> +++ b/drivers/nfc/pn533/pn533.h
> @@ -43,6 +43,11 @@
>  
>  /* Preamble (1), SoPC (2), ACK Code (2), Postamble (1) */
>  #define PN533_STD_FRAME_ACK_SIZE 6
> +/*
> + * Preamble (1), SoPC (2), Packet Length (1), Packet Length Checksum (1),
> + * Specific Application Level Error Code (1) , Postamble (1)
> + */
> +#define PN533_STD_ERROR_FRAME_SIZE 8
>  #define PN533_STD_FRAME_CHECKSUM(f) (f->data[f->datalen])
>  #define PN533_STD_FRAME_POSTAMBLE(f) (f->data[f->datalen + 1])
>  /* Half start code (3), LEN (4) should be 0xffff for extended frame */
> @@ -84,6 +89,9 @@
>  #define PN533_CMD_MI_MASK 0x40
>  #define PN533_CMD_RET_SUCCESS 0x00
>  
> +#define PN533_FRAME_DATALEN_ACK 0x00
> +#define PN533_FRAME_DATALEN_ERROR 0x01
> +#define PN533_FRAME_DATALEN_EXTENDED 0xFF
>  
>  enum  pn533_protocol_type {
>  	PN533_PROTO_REQ_ACK_RESP = 0,
> diff --git a/drivers/nfc/pn533/uart.c b/drivers/nfc/pn533/uart.c
> new file mode 100644
> index 000000000000..f1cc2354a4fd
> --- /dev/null
> +++ b/drivers/nfc/pn533/uart.c
> @@ -0,0 +1,316 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Driver for NXP PN532 NFC Chip - UART transport layer
> + *
> + * Copyright (C) 2018 Lemonage Software GmbH
> + * Author: Lars Pöschel <poeschel@...onage.de>
> + * All rights reserved.
> + */
> +
> +#include <linux/device.h>
> +#include <linux/kernel.h>
> +#include <linux/module.h>
> +#include <linux/nfc.h>
> +#include <linux/netdevice.h>
> +#include <linux/of.h>
> +#include <linux/serdev.h>
> +#include "pn533.h"
> +
> +#define PN532_UART_SKB_BUFF_LEN	(PN533_CMD_DATAEXCH_DATA_MAXLEN * 2)
> +
> +enum send_wakeup {
> +	PN532_SEND_NO_WAKEUP = 0,
> +	PN532_SEND_WAKEUP,
> +	PN532_SEND_LAST_WAKEUP,
> +};
> +
> +
> +struct pn532_uart_phy {
> +	struct serdev_device *serdev;
> +	struct sk_buff *recv_skb;
> +	struct pn533 *priv;
> +	enum send_wakeup send_wakeup;

Could there be any concurrency issues w/ regards to accessing this
variable? I see it is accessed in pn532_uart_send_frame(), pn532_dev_up(),
pn532_dev_down() which may be called from the following wq:

        INIT_WORK(&priv->mi_tm_rx_work, pn533_wq_tm_mi_recv);

        INIT_WORK(&priv->mi_tm_tx_work, pn533_wq_tm_mi_send);

        INIT_DELAYED_WORK(&priv->poll_work, pn533_wq_poll);


and from net/nfc/core.c via dev_up()/dev_down().

> +	struct timer_list cmd_timeout;
> +	struct sk_buff *cur_out_buf;
> +};
> +
> +static int pn532_uart_send_frame(struct pn533 *dev,
> +				struct sk_buff *out)
> +{
> +	/* wakeup sequence and dummy bytes for waiting time */
> +	static const u8 wakeup[] = {
> +		0x55, 0x55, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
> +		0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
> +	struct pn532_uart_phy *pn532 = dev->phy;
> +	int err;
> +
> +	print_hex_dump_debug("PN532_uart TX: ", DUMP_PREFIX_NONE, 16, 1,
> +			     out->data, out->len, false);
> +
> +	pn532->cur_out_buf = out;
> +	if (pn532->send_wakeup) {
> +		err= serdev_device_write(pn532->serdev,
> +				wakeup, sizeof(wakeup),
> +				MAX_SCHEDULE_TIMEOUT);
> +		if (err < 0)
> +			return err;
> +	}
> +
> +	if (pn532->send_wakeup == PN532_SEND_LAST_WAKEUP) {
> +		pn532->send_wakeup = PN532_SEND_NO_WAKEUP;
> +	}
> +
> +	err = serdev_device_write(pn532->serdev, out->data, out->len,
> +			MAX_SCHEDULE_TIMEOUT);
> +	if (err < 0)
> +		return err;
> +
> +	mod_timer(&pn532->cmd_timeout, HZ / 40 + jiffies);
> +	return 0;
> +}
> +
> +static int pn532_uart_send_ack(struct pn533 *dev, gfp_t flags)
> +{
> +	struct pn532_uart_phy *pn532 = dev->phy;
> +	/* spec 7.1.1.3:  Preamble, SoPC (2), ACK Code (2), Postamble */
> +	static const u8 ack[PN533_STD_FRAME_ACK_SIZE] = {
> +			0x00, 0x00, 0xff, 0x00, 0xff, 0x00};
> +	int err;
> +
> +	err = serdev_device_write(pn532->serdev, ack, sizeof(ack),
> +			MAX_SCHEDULE_TIMEOUT);
> +	if (err < 0)
> +		return err;
> +
> +	return 0;
> +}
> +
> +static void pn532_uart_abort_cmd(struct pn533 *dev, gfp_t flags)
> +{
> +	/* An ack will cancel the last issued command */
> +	pn532_uart_send_ack(dev, flags);
> +	/* schedule cmd_complete_work to finish current command execution */
> +	pn533_recv_frame(dev, NULL, -ENOENT);
> +}
> +
> +static void pn532_dev_up(struct pn533 *dev)
> +{
> +	struct pn532_uart_phy *pn532 = dev->phy;
> +
> +	serdev_device_open(pn532->serdev);
> +	pn532->send_wakeup = PN532_SEND_LAST_WAKEUP;
> +}
> +
> +static void pn532_dev_down(struct pn533 *dev)
> +{
> +	struct pn532_uart_phy *pn532 = dev->phy;
> +
> +	serdev_device_close(pn532->serdev);
> +	pn532->send_wakeup = PN532_SEND_WAKEUP;
> +}
> +
> +static struct pn533_phy_ops uart_phy_ops = {
> +	.send_frame = pn532_uart_send_frame,
> +	.send_ack = pn532_uart_send_ack,
> +	.abort_cmd = pn532_uart_abort_cmd,
> +	.dev_up = pn532_dev_up,
> +	.dev_down = pn532_dev_down,
> +};
> +
> +static void pn532_cmd_timeout(struct timer_list *t)
> +{
> +	struct pn532_uart_phy *dev = from_timer(dev, t, cmd_timeout);
> +
> +	pn532_uart_send_frame(dev->priv, dev->cur_out_buf);
> +}
> +
> +/*
> + * scans the buffer if it contains a pn532 frame. It is not checked if the
> + * frame is really valid. This is later done with pn533_rx_frame_is_valid.
> + * This is useful for malformed or errornous transmitted frames. Adjusts the
> + * bufferposition where the frame starts, since pn533_recv_frame expects a
> + * well formed frame.
> + */
> +static int pn532_uart_rx_is_frame(struct sk_buff *skb)
> +{
> +	int i;
> +	u16 frame_len;
> +	struct pn533_std_frame *std;
> +	struct pn533_ext_frame *ext;
> +
> +	for (i = 0; i + PN533_STD_FRAME_ACK_SIZE <= skb->len; i++) {
> +		std = (struct pn533_std_frame *)&skb->data[i];
> +		/* search start code */
> +		if (std->start_frame != cpu_to_be16(PN533_STD_FRAME_SOF))
> +			continue;
> +
> +		/* frame type */
> +		switch (std->datalen) {
> +		case PN533_FRAME_DATALEN_ACK:
> +			if (std->datalen_checksum == 0xff) {
> +				skb_pull(skb, i);
> +				return 1;
> +			}
> +
> +			break;
> +		case PN533_FRAME_DATALEN_ERROR:
> +			if ((std->datalen_checksum == 0xff) &&
> +					(skb->len >=
> +					 PN533_STD_ERROR_FRAME_SIZE)) {
> +				skb_pull(skb, i);
> +				return 1;
> +			}
> +
> +			break;
> +		case PN533_FRAME_DATALEN_EXTENDED:
> +			ext = (struct pn533_ext_frame *)&skb->data[i];
> +			frame_len = ext->datalen;
> +			if (skb->len >= frame_len +
> +					sizeof(struct pn533_ext_frame) +
> +					2 /* CKS + Postamble */) {
> +				skb_pull(skb, i);
> +				return 1;
> +			}
> +
> +			break;
> +		default: /* normal information frame */
> +			frame_len = std->datalen;
> +			if (skb->len >= frame_len +
> +					sizeof(struct pn533_std_frame) +
> +					2 /* CKS + Postamble */) {
> +				skb_pull(skb, i);
> +				return 1;
> +			}
> +
> +			break;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
> +static int pn532_receive_buf(struct serdev_device *serdev,
> +		const unsigned char *data, size_t count)
> +{
> +	struct pn532_uart_phy *dev = serdev_device_get_drvdata(serdev);
> +	size_t i;
> +
> +	del_timer(&dev->cmd_timeout);
> +	for (i = 0; i < count; i++) {
> +		skb_put_u8(dev->recv_skb, *data++);
> +		if (!pn532_uart_rx_is_frame(dev->recv_skb))
> +			continue;
> +
> +		pn533_recv_frame(dev->priv, dev->recv_skb, 0);
> +		dev->recv_skb = alloc_skb(PN532_UART_SKB_BUFF_LEN, GFP_KERNEL);
> +		if (!dev->recv_skb)
> +			return 0;
> +	}
> +
> +	return i;
> +}
> +
> +static struct serdev_device_ops pn532_serdev_ops = {
> +	.receive_buf = pn532_receive_buf,
> +	.write_wakeup = serdev_device_write_wakeup,
> +};
> +
> +static const struct of_device_id pn532_uart_of_match[] = {
> +	{ .compatible = "nxp,pn532", },
> +	{},
> +};
> +MODULE_DEVICE_TABLE(of, pn532_uart_of_match);
> +
> +static int pn532_uart_probe(struct serdev_device *serdev)
> +{
> +	struct pn532_uart_phy *pn532;
> +	struct pn533 *priv;
> +	int err;
> +
> +	err = -ENOMEM;
> +	pn532 = kzalloc(sizeof(*pn532), GFP_KERNEL);
> +	if (!pn532)
> +		goto err_exit;
> +
> +	pn532->recv_skb = alloc_skb(PN532_UART_SKB_BUFF_LEN, GFP_KERNEL);
> +	if (!pn532->recv_skb)
> +		goto err_free;
> +
> +	pn532->serdev = serdev;
> +	serdev_device_set_drvdata(serdev, pn532);
> +	serdev_device_set_client_ops(serdev, &pn532_serdev_ops);
> +	err = serdev_device_open(serdev);
> +	if (err) {
> +		dev_err(&serdev->dev, "Unable to open device\n");
> +		goto err_skb;
> +	}
> +
> +	err = serdev_device_set_baudrate(serdev, 115200);
> +	if (err != 115200) {
> +		err = -EINVAL;
> +		goto err_serdev;
> +	}
> +
> +	serdev_device_set_flow_control(serdev, false);
> +	pn532->send_wakeup = PN532_SEND_WAKEUP;
> +	timer_setup(&pn532->cmd_timeout, pn532_cmd_timeout, 0);
> +	priv = pn53x_common_init(PN533_DEVICE_PN532,
> +				     PN533_PROTO_REQ_ACK_RESP,
> +				     pn532, &uart_phy_ops, NULL,
> +				     &pn532->serdev->dev);
> +	if (IS_ERR(priv)) {
> +		err = PTR_ERR(priv);
> +		goto err_serdev;
> +	}
> +
> +	pn532->priv = priv;
> +	err = pn533_finalize_setup(pn532->priv);
> +	if (err)
> +		goto err_clean;
> +
> +	serdev_device_close(serdev);
> +	err = pn53x_register_nfc(priv, PN533_NO_TYPE_B_PROTOCOLS, &serdev->dev);
> +	if (err) {
> +		pn53x_common_clean(pn532->priv);
> +		goto err_skb;
> +	}
> +
> +	return err;
> +
> +err_clean:
> +	pn53x_common_clean(pn532->priv);
> +err_serdev:
> +	serdev_device_close(serdev);
> +err_skb:
> +	kfree_skb(pn532->recv_skb);
> +err_free:
> +	kfree(pn532);
> +err_exit:
> +	return err;
> +}
> +
> +static void pn532_uart_remove(struct serdev_device *serdev)
> +{
> +	struct pn532_uart_phy *pn532 = serdev_device_get_drvdata(serdev);
> +
> +	pn53x_unregister_nfc(pn532->priv);
> +	serdev_device_close(serdev);
> +	pn53x_common_clean(pn532->priv);
> +	kfree_skb(pn532->recv_skb);
> +	kfree(pn532);
> +}
> +
> +static struct serdev_device_driver pn532_uart_driver = {
> +	.probe = pn532_uart_probe,
> +	.remove = pn532_uart_remove,
> +	.driver = {
> +		.name = "pn532_uart",
> +		.of_match_table = of_match_ptr(pn532_uart_of_match),
> +	},
> +};
> +
> +module_serdev_device_driver(pn532_uart_driver);
> +
> +MODULE_AUTHOR("Lars Pöschel <poeschel@...onage.de>");
> +MODULE_DESCRIPTION("PN532 UART driver");
> +MODULE_LICENSE("GPL");
> 

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