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>

diff --git a/drivers/iio/adc/mcp320x.c b/drivers/iio/adc/mcp320x.c
index 06bc2453caf93a6de83fb9f1ea6acafffe3eb573..78a4955d5e2bd6d313e9129b108f746e4e74f324 100644 (file)
--- a/drivers/iio/adc/mcp320x.c
+++ b/drivers/iio/adc/mcp320x.c
@@ -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))