spi: rockchip: fix missing error on unsupported SPI_CS_HIGH

[ Upstream commit d5d933f09a ]

The hardware (except for the ROCKCHIP_SPI_VER2_TYPE2 version) does not
support active-high native chip selects. However if such a CS is configured
the core does not error as it normally should, because the
'ctlr->use_gpio_descriptors = true' line in rockchip_spi_probe() makes the
core set SPI_CS_HIGH in ctlr->mode_bits.

In such a case the spi-rockchip driver operates normally but produces an
active-low chip select signal without notice.

There is no provision in the current core code to handle this
situation. Fix by adding a check in the ctlr->setup function (similarly to
what spi-atmel.c does).

This cannot be done reading the SPI_CS_HIGH but in ctlr->mode_bits because
that bit gets always set by the core for master mode (see above).

Fixes: eb1262e3cc ("spi: spi-rockchip: use num-cs property and ctlr->enable_gpiods")
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Link: https://lore.kernel.org/r/20220421213251.1077899-1-luca.ceresoli@bootlin.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>

drivers/spi/spi-rockchip.c

@@ -196,6 +196,8 @@ struct rockchip_spi {
 
 	bool slave_abort;
 	bool cs_inactive; /* spi slave tansmition stop when cs inactive */
+	bool cs_high_supported; /* native CS supports active-high polarity */
+
 	struct spi_transfer *xfer; /* Store xfer temporarily */
 };
 
@@ -718,6 +720,11 @@ static int rockchip_spi_setup(struct spi_device *spi)
 	struct rockchip_spi *rs = spi_controller_get_devdata(spi->controller);
 	u32 cr0;
 
+	if (!spi->cs_gpiod && (spi->mode & SPI_CS_HIGH) && !rs->cs_high_supported) {
+		dev_warn(&spi->dev, "setup: non GPIO CS can't be active-high\n");
+		return -EINVAL;
+	}
+
 	pm_runtime_get_sync(rs->dev);
 
 	cr0 = readl_relaxed(rs->regs + ROCKCHIP_SPI_CTRLR0);
@@ -898,6 +905,7 @@ static int rockchip_spi_probe(struct platform_device *pdev)
 
 	switch (readl_relaxed(rs->regs + ROCKCHIP_SPI_VERSION)) {
 	case ROCKCHIP_SPI_VER2_TYPE2:
+		rs->cs_high_supported = true;
 		ctlr->mode_bits |= SPI_CS_HIGH;
 		if (ctlr->can_dma && slave_mode)
 			rs->cs_inactive = true;