spi: imx: Implement support for CS_WORD

This only works when the native chipselect is in use. On a board with a
Ti ADS7950 8 channel ADC. This patch reduces the time to read out all
channels once from 280 us to 20 us.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20210727124226.5571-1-u.kleine-koenig@pengutronix.de
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-imx.c b/drivers/spi/spi-imx.c
index 593b63be73de82b38ae47dc476b61e24511eeabc..340fd1245bc26e5642080ebd28045a4dad05e770 100644 (file)
--- a/drivers/spi/spi-imx.c
+++ b/drivers/spi/spi-imx.c
@@ -1176,6 +1176,7 @@ static int spi_imx_setupxfer(struct spi_device *spi,
         * dynamic_burst in that case.
         */
        if (spi_imx->devtype_data->dynamic_burst && !spi_imx->slave_mode &&
+           !(spi->mode & SPI_CS_WORD) &&
            (spi_imx->bits_per_word == 8 ||
            spi_imx->bits_per_word == 16 ||
            spi_imx->bits_per_word == 32)) {
@@ -1611,6 +1612,15 @@ static int spi_imx_probe(struct platform_device *pdev)
            is_imx53_ecspi(spi_imx))
                spi_imx->bitbang.master->mode_bits |= SPI_LOOP | SPI_READY;
 
+       if (is_imx51_ecspi(spi_imx) &&
+           device_property_read_u32(&pdev->dev, "cs-gpios", NULL))
+               /*
+                * When using HW-CS implementing SPI_CS_WORD can be done by just
+                * setting the burst length to the word size. This is
+                * considerably faster than manually controlling the CS.
+                */
+               spi_imx->bitbang.master->mode_bits |= SPI_CS_WORD;
+
        spi_imx->spi_drctl = spi_drctl;
 
        init_completion(&spi_imx->xfer_done);