Message-ID: <48F8467C.5010902@mimc.co.uk>
Date: Fri, 17 Oct 2008 09:02:04 +0100
From: Mark Jackson <mpfj@mimc.co.uk>
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To: dbrownell@users.sourceforge.net
CC: Alessandro Zummo <alessandro.zummo@towertech.it>,
       rtc-linux@googlegroups.com, lkml <linux-kernel@vger.kernel.org>,
       spi-devel-general@lists.sourceforge.net
Subject: Re: [PATCH] Add Dallas DS1390 RTC chip
References: <48F452BE.2030901@mimc.co.uk> <20081014101703.1ded0259@i1501.lan.towertech.it>
In-Reply-To: <20081014101703.1ded0259@i1501.lan.towertech.it>
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David ... please see comments below regarding spi buffers ...

Regards
Mark

Alessandro Zummo wrote:
> On Tue, 14 Oct 2008 09:05:18 +0100
> Mark Jackson <mpfj@mimc.co.uk> wrote:
> 
>  Hi Mark,
> 
>    a few notes below:
> 
>> +#include <linux/module.h>
>> +#include <linux/version.h>
>> +
>> +#include <linux/kernel.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/init.h>
>> +#include <linux/rtc.h>
>> +#include <linux/spi/spi.h>
>> +#include <linux/bcd.h>
>> +#include <linux/delay.h>
> 
>  Please check that you require all of those includes.
> 
> 
>> +struct ds1390
>> +{
>> +	struct rtc_device *rtc;
>> +	u8 buf[9];	/* cmd + 8 registers */
>> +	u8 tx_buf[2];
>> +	u8 rx_buf[2];
>> +};
>> +
>> +static void ds1390_set_reg(struct device *dev, unsigned char address,
>> +				unsigned char data)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	unsigned char buf[2];
>> +
>> +	/* MSB must be '1' to write */
>> +	buf[0] = address | 0x80;
>> +	buf[1] = data;
>> +
>> +	spi_write(spi, buf, 2);
>> +}
>> +
>> +static int ds1390_get_reg(struct device *dev, unsigned char address,
>> +				unsigned char *data)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	struct ds1390 *chip = dev_get_drvdata(dev);
>> +	struct spi_message message;
>> +	struct spi_transfer xfer;
>> +	int status;
>> +
>> +	if (!data)
>> +		return -EINVAL;
>> +
>> +	/* Build our spi message */
>> +	spi_message_init(&message);
>> +	memset(&xfer, 0, sizeof(xfer));
>> +	xfer.len = 2;
>> +	/* Can tx_buf and rx_buf be equal? The doc in spi.h is not sure... */
>> +	xfer.tx_buf = chip->tx_buf;
>> +	xfer.rx_buf = chip->rx_buf;
> 
>  you use the same buffer a few functions below. either
>  one way or the other. please investigate with the spi subsystem maintainer.

David,

Just to double check (as per Alessandro's suggestion), is this okay use of the 
spi buffers ?

I took the code from an existing RTC driver (rtc-max6902), so I am assuming that
this code has already passed judgement.

> 
> 
>> +
>> +	/* Clear MSB to indicate read */
>> +	chip->tx_buf[0] = address & 0x7f;
>> +
>> +	spi_message_add_tail(&xfer, &message);
>> +
>> +	/* do the i/o */
>> +	status = spi_sync(spi, &message);
>> +	if (status == 0)
>> +	{
>> +		status = message.status;
>> +	}
>> +	else
>> +	{
>> +		return status;
>> +	}
> 
>  should be cleaner in this way:
> 
>  if (status != 0)
> 	return status;
> 
>  *data = chip->rx_buf[1];
> 
>  return message.status;
> 
> 
>> +static int ds1390_get_datetime(struct device *dev, struct rtc_time *dt)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	struct ds1390 *chip = dev_get_drvdata(dev);
>> +	struct spi_message message;
>> +	struct spi_transfer xfer;
>> +	int status;
>> +
>> +	/* build the message */
>> +	spi_message_init(&message);
>> +	memset(&xfer, 0, sizeof(xfer));
>> +	xfer.len = 1 + 7;	/* read command + 7 registers */
>> +	xfer.tx_buf = chip->buf;
>> +	xfer.rx_buf = chip->buf;
> 
>  the buffer mentioned above.

... see text above ...

> 
> 
>> +	chip->buf[0] = DS1390_REG_SECONDS;
>> +	spi_message_add_tail(&xfer, &message);
>> +
>> +	/* do the i/o */
>> +	status = spi_sync(spi, &message);
>> +	if (status == 0)
>> +	{
>> +		status = message.status;
>> +	}
>> +	else
>> +	{
>> +		return status;
>> +	}
> 
>  ditto.
> 
>> +	/* The chip sends data in this order:
>> +	 * Seconds, Minutes, Hours, Day, Date, Month / Century, Year */
>> +	dt->tm_sec	= BCD2BIN(chip->buf[1]);
>> +	dt->tm_min	= BCD2BIN(chip->buf[2]);
>> +	dt->tm_hour	= BCD2BIN(chip->buf[3]);
>> +	dt->tm_wday	= BCD2BIN(chip->buf[4]);
>> +	dt->tm_mday	= BCD2BIN(chip->buf[5]);
>> +	/* mask off century bit */
>> +	dt->tm_mon	= BCD2BIN(chip->buf[6] & 0x7f) - 1;
>> +	/* adjust for century bit */
>> +	dt->tm_year = BCD2BIN(chip->buf[7]) + ((chip->buf[6] & 0x80) ? 100 : 0);
>> +
>> +	return 0;
>> +}
>> +
>> +static int ds1390_set_datetime(struct device *dev, struct rtc_time *dt)
>> +{
>> +	struct spi_device *spi = to_spi_device(dev);
>> +	struct ds1390 *chip = dev_get_drvdata(dev);
>> +	struct spi_message message;
>> +	struct spi_transfer xfer;
>> +	int status;
>> +
>> +	/* build the message */
>> +	spi_message_init(&message);
>> +	memset(&xfer, 0, sizeof(xfer));
>> +	xfer.len = 1 + 8;	/* write command + 8 registers */
>> +	xfer.tx_buf = chip->buf;
>> +	xfer.rx_buf = chip->buf;

... and I guess here as well ... ???

>> +	chip->buf[0] = DS1390_REG_SECONDS | 0x80;
>> +	chip->buf[1] = BIN2BCD(dt->tm_sec);
>> +	chip->buf[2] = BIN2BCD(dt->tm_min);
>> +	chip->buf[3] = BIN2BCD(dt->tm_hour);
>> +	chip->buf[4] = BIN2BCD(dt->tm_wday);
>> +	chip->buf[5] = BIN2BCD(dt->tm_mday);
>> +	chip->buf[6] = BIN2BCD(dt->tm_mon + 1) | ((dt->tm_year > 99) ? 0x80 : 0x00);
>> +	chip->buf[7] = BIN2BCD(dt->tm_year % 100);
>> +	spi_message_add_tail(&xfer, &message);
>> +
>> +	/* do the i/o */
>> +	status = spi_sync(spi, &message);
>> +	if (status == 0)
>> +	{
>> +		status = message.status;
>> +	}
>> +	else
>> +	{
>> +		return status;
>> +	}
> 
>  if status == 0, status is not used anymore, so you can
>  just return if != 0;
> 
>> +	return 0;
>> +}
>> +
>> +static int ds1390_read_time(struct device *dev, struct rtc_time *tm)
>> +{
>> +	return ds1390_get_datetime(dev, tm);
>> +}
>> +
>> +static int ds1390_set_time(struct device *dev, struct rtc_time *tm)
>> +{
>> +	return ds1390_set_datetime(dev, tm);
>> +}
>> +
>> +static const struct rtc_class_ops ds1390_rtc_ops = {
>> +	.read_time	= ds1390_read_time,
>> +	.set_time	= ds1390_set_time,
>> +};
>> +
>> +static int __devinit ds1390_probe(struct spi_device *spi)
>> +{
>> +	struct rtc_device *rtc;
>> +	unsigned char tmp;
>> +	struct ds1390 *chip;
>> +	int res;
>> +
>> +	printk("DS1390 SPI RTC driver\n");
>> +
>> +	rtc = rtc_device_register("ds1390",
>> +				&spi->dev, &ds1390_rtc_ops, THIS_MODULE);
>> +	if (IS_ERR(rtc))
>> +	{
>> +		printk("RTC : unable to register device\n");
>> +		return PTR_ERR(rtc);
>> +	}
>> +
>> +	spi->mode = SPI_MODE_3;
>> +	spi->bits_per_word = 8;
>> +	spi_setup(spi);
>> +
>> +	chip = kzalloc(sizeof *chip, GFP_KERNEL);
>> +	if (!chip) {
>> +		printk("RTC : unable to allocate device memory\n");
>> +		rtc_device_unregister(rtc);
>> +		return -ENOMEM;
>> +	}
>> +	chip->rtc = rtc;
>> +	dev_set_drvdata(&spi->dev, chip);
>> +
>> +	res = ds1390_get_reg(&spi->dev, DS1390_REG_SECONDS, &tmp);
>> +	if (res) {
>> +		printk("RTC : unable to read device\n");
>> +		rtc_device_unregister(rtc);
>> +		return res;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>> +static int __devexit ds1390_remove(struct spi_device *spi)
>> +{
>> +	struct ds1390 *chip = platform_get_drvdata(spi);
>> +	struct rtc_device *rtc = chip->rtc;
>> +
>> +	if (rtc)
>> +		rtc_device_unregister(rtc);
>> +
>> +	kfree(chip);
>> +
>> +	return 0;
>> +}
>> +
>> +static struct spi_driver ds1390_driver = {
>> +	.driver = {
>> +		.name	= "rtc-ds1390",
>> +		.bus	= &spi_bus_type,
>> +		.owner	= THIS_MODULE,
>> +	},
>> +	.probe	= ds1390_probe,
>> +	.remove = __devexit_p(ds1390_remove),
>> +};
>> +
>> +static __init int ds1390_init(void)
>> +{
>> +	return spi_register_driver(&ds1390_driver);
>> +}
>> +module_init(ds1390_init);
>> +
>> +static __exit void ds1390_exit(void)
>> +{
>> +	spi_unregister_driver(&ds1390_driver);
>> +}
>> +module_exit(ds1390_exit);
>> +
>> +MODULE_DESCRIPTION ("DS1390 SPI RTC driver");
>> +MODULE_AUTHOR ("Mark Jackson");
> 
>  you email here please.
> 
>> +MODULE_LICENSE ("GPL");
> 
> 
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