[PATCH V2 6/9] spi: bcm2835aux: warn in dmesg that native cs is not really supported

kernel
2019-03-24T17:51:45Z

From personal bad experience (even as the author of the original driver)
it shows that native-cs is "somewhat" supported by the spi bus driver
when using a buggy device tree.

So make sure that the driver is warning in dmesg about this fact
that we are running in a not supported mode that may have surprizing
limitations.

Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
Fixes: 1ea29b39f4c812ece2f936065a0a3d6fe44a263e
---
drivers/spi/spi-bcm2835aux.c | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
index c8acde017b6a..6af07dec5fdc 100644
--- a/drivers/spi/spi-bcm2835aux.c
+++ b/drivers/spi/spi-bcm2835aux.c
@@ -396,6 +396,38 @@ static void bcm2835aux_spi_handle_err(struct spi_master *master,
bcm2835aux_spi_reset_hw(bs);
}

+static int bcm2835aux_spi_setup(struct spi_device *spi)
+{
+ int ret;
+
+ if (spi->mode & SPI_NO_CS)
+ return 0;
+ /* sanity check for native cs */
+ if (!gpio_is_valid(spi->cs_gpio)) {
+ /* for dt-backwards compatibility: only support native on CS0
+ * known things not supported with broken native CS:
+ * * multiple chip-selects: cs0-cs2 are all
+ * simultaniously asserted whenever there is a transfer
+ * this even includes SPI_NO_CS
+ * * SPI_CS_HIGH: cs are always asserted low
+ * * cs_change: cs is deasserted after each spi_transfer
+ * * cs_delay_usec: cs is always deasserted one SCK cycle
+ * after the last transfer
+ * probably more...
+ */
+ if (spi->chip_select == 0) {
+ dev_err(&spi->dev,
+ "native CS is not supported but may work for some use-cases for cs = 0 - please define a valid value cs-gpios in DT for complete feature set\n");
+ return 0;
+ }
+ dev_err(&spi->dev,
+ "native CS is not supported for cs > 0 - please define a valid value cs-gpios in DT to enable multiple cs\n");
+ return -EINVAL;
+ }
+
+ return 0;
+}
+
static int bcm2835aux_spi_probe(struct platform_device *pdev)
{
struct spi_master *master;
@@ -425,6 +457,7 @@ static int bcm2835aux_spi_probe(struct platform_device *pdev)
* a spi_transfer
*/
master->num_chipselect = 1;
+ master->setup = bcm2835aux_spi_setup;
master->transfer_one = bcm2835aux_spi_transfer_one;
master->handle_err = bcm2835aux_spi_handle_err;
master->prepare_message = bcm2835aux_spi_prepare_message;