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Date: Sun, 20 Mar 2016 17:12:20 +0100
From: Joachim Eastwood <manabian@...il.com>
To: Slawomir Stepien <sst@...zta.fm>
Cc: Jonathan Cameron <jic23@...nel.org>,
Hartmut Knaack <knaack.h@....de>,
Lars-Peter Clausen <lars@...afoo.de>,
Peter Meerwald-Stadler <pmeerw@...erw.net>,
linux-iio@...r.kernel.org,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] iio: add driver for Microchip MCP413X/414X/415X/416X/423X/424X/425X/426X
Hi Slawomir,
On 20 March 2016 at 15:30, Slawomir Stepien <sst@...zta.fm> wrote:
> The following functionalities are supported:
> - write, read from volatile memory
I think it would be useful if you could put 'potentiometer' either in
the subject and/or commit text so it is more obvious what this driver
is for.
> Datasheet: http://ww1.microchip.com/downloads/en/DeviceDoc/22060b.pdf
>
> Signed-off-by: Slawomir Stepien <sst@...zta.fm>
> +
> +struct mcp4131_data {
> + struct spi_device *spi;
> + const struct mcp4131_cfg *cfg;
> + struct mutex lock;
> + struct spi_transfer xfer;
> + struct spi_message msg;
> + u8 buf[2] ____cacheline_aligned;
> +};
> +
> +#define MCP4131_CHANNEL(ch) { \
> + .type = IIO_RESISTANCE, \
> + .indexed = 1, \
> + .output = 1, \
> + .channel = (ch), \
> + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
> + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
> +}
> +
> +static const struct iio_chan_spec mcp4131_channels[] = {
> + MCP4131_CHANNEL(0),
> + MCP4131_CHANNEL(1),
> +};
> +
> +static int mcp4131_exec(struct mcp4131_data *data,
> + u8 addr, u8 cmd,
> + u16 val)
> +{
> + int err;
> + struct spi_device *spi = data->spi;
> +
> + data->xfer.tx_buf = data->buf;
> + data->xfer.rx_buf = data->buf;
> +
> + switch (cmd) {
> + case MCP4131_READ:
> + data->xfer.len = 2; /* Two bytes transfer for this command */
> + data->buf[0] = (addr << MCP4131_WIPER_SHIFT) | MCP4131_READ;
> + data->buf[1] = 0;
> + break;
> +
> + case MCP4131_WRITE:
> + data->xfer.len = 2;
> + data->buf[0] = (addr << MCP4131_WIPER_SHIFT) |
> + MCP4131_WRITE | (val >> 8);
> + data->buf[1] = val & 0xFF; /* 8 bits here */
> + break;
> +
> + default:
> + return -EINVAL;
> + }
> +
> + dev_dbg(&spi->dev, "mcp4131_exec: tx0: 0x%x tx1: 0x%x\n",
> + data->buf[0], data->buf[1]);
> +
> + spi_message_init(&data->msg);
> + spi_message_add_tail(&data->xfer, &data->msg);
> +
> + err = spi_sync(spi, &data->msg);
> + if (err) {
> + dev_err(&spi->dev, "spi_sync(): %d\n", err);
> + return err;
> + }
Isn't this init, add, sync sequence basically open coding of what
spi_write/spi_read does?
If you could use those you could also get rid transfer/message structs
in priv data.
Also it these any reason why the data buffer can just be a local
variable in mcp4131_read_raw/mcp4131_write_raw?
If it could be I think it should be possible to move the lock into the
mcp4131_exec function.
> +
> + dev_dbg(&spi->dev, "mcp4131_exec: rx0: 0x%x rx1: 0x%x\n",
> + data->buf[0], data->buf[1]);
> +
> + return 0;
> +}
> +
> +static int mcp4131_read_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan,
> + int *val, int *val2, long mask)
> +{
> + int err;
> + struct mcp4131_data *data = iio_priv(indio_dev);
> + int address = chan->channel;
> +
> + mutex_lock(&data->lock);
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_RAW:
> + err = mcp4131_exec(data, address, MCP4131_READ, 0);
> + if (err) {
> + mutex_unlock(&data->lock);
> + return err;
> + }
> +
> + /* Error, bad address/command combination */
> + if (!MCP4131_CMDERR(data->buf)) {
> + mutex_unlock(&data->lock);
> + return -EIO;
> + }
> +
> + *val = MCP4131_RAW(data->buf);
> + mutex_unlock(&data->lock);
> + return IIO_VAL_INT;
> +
> + case IIO_CHAN_INFO_SCALE:
> + *val = 1000 * data->cfg->kohms;
> + *val2 = data->cfg->max_pos;
> + mutex_unlock(&data->lock);
Is locking really necessary for IIO_CHAN_INFO_SCALE?
Isn't all data->cfg stuff constant?
> + return IIO_VAL_FRACTIONAL;
> + }
> +
> + mutex_unlock(&data->lock);
> +
> + return -EINVAL;
> +}
> +
> +static int mcp4131_write_raw(struct iio_dev *indio_dev,
> + struct iio_chan_spec const *chan,
> + int val, int val2, long mask)
> +{
> + int err;
> + struct mcp4131_data *data = iio_priv(indio_dev);
> + int address = chan->channel << MCP4131_WIPER_SHIFT;
> +
> + mutex_lock(&data->lock);
> +
> + switch (mask) {
> + case IIO_CHAN_INFO_RAW:
> + if (val > data->cfg->max_pos || val < 0) {
> + mutex_unlock(&data->lock);
> + return -EINVAL;
> + }
> + break;
> + default:
> + mutex_unlock(&data->lock);
> + return -EINVAL;
> + }
> +
> + err = mcp4131_exec(data, address, MCP4131_WRITE, val);
> + mutex_unlock(&data->lock);
While this is not a huge function it is usually good practice to keep
the locking scope as small as possible.
So wouldn't this be sufficient here.
mutex_lock(&data->lock);
err = mcp4131_exec(data, address, MCP4131_WRITE, val);
mutex_unlock(&data->lock);
Of course if you are able move the lock into mcp4131_exec this will go away.
regards,
Joachim Eastwood
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