Applied "spi: bcm2835aux: warn in dmesg that native cs is not really supported" to the spi tree

[Mark Brown <broonie@xxxxxxxxxx>]

The patch

   spi: bcm2835aux: warn in dmesg that native cs is not really supported

has been applied to the spi tree at

   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 519f2c22a6c71a9fefed1166c36d48246e010514 Mon Sep 17 00:00:00 2001
From: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
Date: Sat, 30 Mar 2019 09:31:03 +0000
Subject: [PATCH] spi: bcm2835aux: warn in dmesg that native cs is not really
 supported

>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.

Fixes: 1ea29b39f4c812ec ("spi: bcm2835aux: add bcm2835 auxiliary spi device...")
Signed-off-by: Martin Sperl <kernel@xxxxxxxxxxxxxxxx>
Acked-by: Stefan Wahren <stefan.wahren@xxxxxxxx>
Signed-off-by: Mark Brown <broonie@xxxxxxxxxx>
---
 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..a105db371417 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;
+
+	/* sanity check for native cs */
+	if (spi->mode & SPI_NO_CS)
+		return 0;
+	if (gpio_is_valid(spi->cs_gpio))
+		return 0;
+
+	/* 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...
+	 */
+	dev_warn(&spi->dev,
+		 "Native CS is not supported - please configure cs-gpio in device-tree\n");
+
+	if (spi->chip_select == 0)
+		return 0;
+
+	dev_warn(&spi->dev, "Native CS is not working for cs > 0\n");
+
+	return -EINVAL;
+}
+
 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;
-- 
2.20.1