spi: bitbang: Make chipselect callback optional

The ->chipselect() callback on the bit-banged SPI library
master is optional if using GPIO descriptors: when using
descriptors exclusively without any native chipselects,
the core does not even call out the the native ->set_cs()
and therefore ->chipselect() on a bit-banged SPI master
will not even be called in this case.

Make sure to respect the SPI_MASTER_GPIO_SS as used by
e.g. spi-gpio.c though: this setting will make the core
handle the chip select using GPIO descriptors *AND* call
the local chipselect handler.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20191205091340.59850-1-linus.walleij@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi-bitbang.c b/drivers/spi/spi-bitbang.c
index d84e22d..68491a8 100644 (file)
--- a/drivers/spi/spi-bitbang.c
+++ b/drivers/spi/spi-bitbang.c
@@ -329,8 +329,20 @@ static void spi_bitbang_set_cs(struct spi_device *spi, bool enable)
 int spi_bitbang_init(struct spi_bitbang *bitbang)
 {
        struct spi_master *master = bitbang->master;
+       bool custom_cs;
 
-       if (!master || !bitbang->chipselect)
+       if (!master)
+               return -EINVAL;
+       /*
+        * We only need the chipselect callback if we are actually using it.
+        * If we just use GPIO descriptors, it is surplus. If the
+        * SPI_MASTER_GPIO_SS flag is set, we always need to call the
+        * driver-specific chipselect routine.
+        */
+       custom_cs = (!master->use_gpio_descriptors ||
+                    (master->flags & SPI_MASTER_GPIO_SS));
+
+       if (custom_cs && !bitbang->chipselect)
                return -EINVAL;
 
        mutex_init(&bitbang->lock);
@@ -344,7 +356,12 @@ int spi_bitbang_init(struct spi_bitbang *bitbang)
        master->prepare_transfer_hardware = spi_bitbang_prepare_hardware;
        master->unprepare_transfer_hardware = spi_bitbang_unprepare_hardware;
        master->transfer_one = spi_bitbang_transfer_one;
-       master->set_cs = spi_bitbang_set_cs;
+       /*
+        * When using GPIO descriptors, the ->set_cs() callback doesn't even
+        * get called unless SPI_MASTER_GPIO_SS is set.
+        */
+       if (custom_cs)
+               master->set_cs = spi_bitbang_set_cs;
 
        if (!bitbang->txrx_bufs) {
                bitbang->use_dma = 0;