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iio: adc: mcp320x: Speed up readout of single-channel ADCs 

Single-channel converters such as mcp3001, mcp3201, mcp3301 and the
upcoming mcp3550/1/3 lack a MOSI pin, so there's no need to call
mcp320x_channel_to_tx_data() for them.

Moreover, instead of calling spi_read() for these converters, which
generates an spi_message and spi_transfer on the stack on every readout,
it's more efficient to use the spi_message and spi_transfer[] included
in struct mcp320x (as we do for multi-channel ADCs), but initialize the
spi_message only with the receive transfer.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
hifive-unleashed-5.1
Lukas Wunner 2017-09-09 20:32:41 +02:00 committed by Jonathan Cameron
parent f1f065d7ac
commit ea9103186d
1 changed files with 14 additions and 20 deletions
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34
drivers/iio/adc/mcp320x.c
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@ -76,10 +76,6 @@ static int mcp320x_channel_to_tx_data(int device_index,
int start_bit = 1;
switch (device_index) {
case mcp3001:
case mcp3201:
case mcp3301:
return 0;
case mcp3002:
case mcp3202:
return ((start_bit << 4) | (!differential << 3) |
@ -100,20 +96,14 @@ static int mcp320x_adc_conversion(struct mcp320x *adc, u8 channel,
{
int ret;
adc->rx_buf[0] = 0;
adc->rx_buf[1] = 0;
adc->tx_buf = mcp320x_channel_to_tx_data(device_index,
channel, differential);
memset(&adc->rx_buf, 0, sizeof(adc->rx_buf));
if (adc->chip_info->num_channels > 1)
adc->tx_buf = mcp320x_channel_to_tx_data(device_index, channel,
differential);
if (device_index != mcp3001 && device_index != mcp3201 && device_index != mcp3301) {
ret = spi_sync(adc->spi, &adc->msg);
if (ret < 0)
return ret;
} else {
ret = spi_read(adc->spi, &adc->rx_buf, sizeof(adc->rx_buf));
if (ret < 0)
return ret;
}
ret = spi_sync(adc->spi, &adc->msg);
if (ret < 0)
return ret;
switch (device_index) {
case mcp3001:
@ -322,9 +312,13 @@ static int mcp320x_probe(struct spi_device *spi)
adc->transfer[0].len = sizeof(adc->tx_buf);
adc->transfer[1].rx_buf = adc->rx_buf;
adc->transfer[1].len = sizeof(adc->rx_buf);
spi_message_init_with_transfers(&adc->msg, adc->transfer,
ARRAY_SIZE(adc->transfer));
if (chip_info->num_channels == 1)
/* single-channel converters are rx only (no MOSI pin) */
spi_message_init_with_transfers(&adc->msg,
&adc->transfer[1], 1);
else
spi_message_init_with_transfers(&adc->msg, adc->transfer,
ARRAY_SIZE(adc->transfer));
adc->reg = devm_regulator_get(&spi->dev, "vref");
if (IS_ERR(adc->reg))