linux-kernel - Re: [PATCH] hwmon: Driver for as1531, Austria-Microsystem Analog to Digital Converter.

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Date:	Wed, 18 May 2011 14:09:13 +0100
From:	Jonathan Cameron <jic23@....ac.uk>
To:	fabien.marteau@...adeus.com
CC:	khali@...ux-fr.org, guenter.roeck@...csson.com,
	linux-kernel@...r.kernel.org, lm-sensors@...sensors.org
Subject: Re: [PATCH] hwmon: Driver for as1531, Austria-Microsystem Analog
 to Digital Converter.

On 05/16/11 14:39, fabien.marteau@...adeus.com wrote:
> From: Fabien Marteau <fabien.marteau@...adeus.com>
> 
Had a few minutes so done a quick port to IIO with minimal code changes.
Now looking at cleaning things up so actually reading the code rather
than cut and paste.  The message is somewhat 'novel'. 

...

So we have a spi device that only talks in 1 bit words?
1) I'm amazed any spi controllers support that.
2) Doesn't look necessary from the data sheet google furnished me with.

Looks like it will quite happily work with 8 bit transfers. Suggested replacement code below.
> +static int as1531_message(struct spi_device *spi, int cmd, int *ret_value)
> +{
> +	struct spi_message	message;
> +	struct spi_transfer	x[1];
> +	int status, i;
> +	u8	cmd_send;
> +	unsigned char buf[64];
> +	unsigned char buf_read[64];
> +
> +	cmd_send = cmd;
> +
> +	spi_message_init(&message);
> +	memset(x, 0, sizeof x);
> +	memset(buf, 0, sizeof(buf));
> +	memset(buf_read, 0, sizeof(buf_read));
> +
> +	for (i = 0; i < 8; i++) {
> +		buf[i] = ((cmd_send & 0x80)>>7);
> +		cmd_send = cmd_send << 1;
> +	}
> +
> +	x[0].tx_buf = buf;
> +	x[0].len = 24;
> +	x[0].rx_buf = buf_read;
> +	x[0].speed_hz = AS1531_SPI_SPEED;
> +	x[0].bits_per_word = 1;
> +	spi_message_add_tail(&x[0], &message);
> +
> +	status = spi_sync(spi, &message);
> +	if (status < 0)
> +		return status;
> +
> +	*ret_value = buf_read[11] & 0x01;
> +	for (i = 12; i < 23 ; i++) {
> +		*ret_value = *ret_value << 1;
> +		*ret_value = *ret_value | (buf_read[i]&0x01);
> +	}
> +
> +	return 0;
> +}
static int as1531_message(struct spi_device *spi, int cmd, u16 *ret_value)
{
	int status;
	u8 cmd_send = cmd;
	struct spi_message message;
	struct spi_transfer x[2] = {
		{
			.len = 1,
			/* this should be default anyway - so could drop */
			.bits_per_word = 8,
			/* This should be set in board config really */
			.speed_hz = AS1531_SPI_SPEED,
			.rx_buf = &cmd_send,
		}, {
			.len = 2,
			.bits_per_word = 8,
			.speed_hz = AS1531_SPI_SPEED,
			.tx_buf = ret_value,
		}
	};

	spi_message_init(&message);
	spi_message_add_tail(&x[0], &message);
	spi_message_add_tail(&x[1], &message);

	status = spi_sync(spi, &message);
	if (status < 0)
		return status;

	*ret_value = (be16_to_cpup(ret_value) >> 2) & 0xFFF;

	return 0;
}

Obviously also requires changing the type of the element passed
as ret_value.  Could set the bits_per_word of the second transfer
to 16 and avoid the endianness conversion, but I'm not sure how
many spi masters support that.

Jonathan
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