[PATCH 6/7] spi: atmel: Improve and fix GPIO CS usage

[Gregory CLEMENT <gregory.clement@bootlin.com>]

In the previous implementation of this driver, the index of the GPIO
used as CS was linked to the offset of the CS register used to
configure the transfer.

With this new implementation the first CS register not used by
internal CS is associated to all the GPIO CS. It allows to not be
anymore limited to have only 4 CS managed, now it is possible to have
in the same time until 3 internal CS and no more limit for the CS
GPIO.

Signed-off-by: Gregory CLEMENT <gregory.clement@bootlin.com>
---
 drivers/spi/spi-atmel.c | 74 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 66 insertions(+), 8 deletions(-)

diff --git a/drivers/spi/spi-atmel.c b/drivers/spi/spi-atmel.c
index 1ff5b20eabf7..ac5e2ddf9e1b 100644
--- a/drivers/spi/spi-atmel.c
+++ b/drivers/spi/spi-atmel.c
@@ -280,6 +280,8 @@ struct atmel_spi {
 	bool			cs_active;
 
 	u32			fifo_size;
+	u8			native_cs_free;
+	u8			native_cs_for_gpio;
 };
 
 /* Controller-specific per-slave state */
@@ -324,23 +326,29 @@ static bool atmel_spi_is_v2(struct atmel_spi *as)
 static void cs_activate(struct atmel_spi *as, struct spi_device *spi)
 {
 	struct atmel_spi_device *asd = spi->controller_state;
+	int chip_select;
 	u32 mr;
 
+	if (spi->cs_gpiod)
+		chip_select = as->native_cs_for_gpio;
+	else
+		chip_select = spi->chip_select;
+
 	if (atmel_spi_is_v2(as)) {
-		spi_writel(as, CSR0 + 4 * spi->chip_select, asd->csr);
+		spi_writel(as, CSR0 + 4 * chip_select, asd->csr);
 		/* For the low SPI version, there is a issue that PDC transfer
 		 * on CS1,2,3 needs SPI_CSR0.BITS config as SPI_CSR1,2,3.BITS
 		 */
 		spi_writel(as, CSR0, asd->csr);
 		if (as->caps.has_wdrbt) {
 			spi_writel(as, MR,
-					SPI_BF(PCS, ~(0x01 << spi->chip_select))
+					SPI_BF(PCS, ~(0x01 << chip_select))
 					| SPI_BIT(WDRBT)
 					| SPI_BIT(MODFDIS)
 					| SPI_BIT(MSTR));
 		} else {
 			spi_writel(as, MR,
-					SPI_BF(PCS, ~(0x01 << spi->chip_select))
+					SPI_BF(PCS, ~(0x01 << chip_select))
 					| SPI_BIT(MODFDIS)
 					| SPI_BIT(MSTR));
 		}
@@ -362,7 +370,7 @@ static void cs_activate(struct atmel_spi *as, struct spi_device *spi)
 		}
 
 		mr = spi_readl(as, MR);
-		mr = SPI_BFINS(PCS, ~(1 << spi->chip_select), mr);
+		mr = SPI_BFINS(PCS, ~(1 << chip_select), mr);
 		if (spi->cs_gpiod && spi->chip_select != 0)
 			gpiod_set_value(spi->cs_gpiod, 1);
 		spi_writel(as, MR, mr);
@@ -373,13 +381,19 @@ static void cs_activate(struct atmel_spi *as, struct spi_device *spi)
 
 static void cs_deactivate(struct atmel_spi *as, struct spi_device *spi)
 {
+	int chip_select;
 	u32 mr;
 
+	if (spi->cs_gpiod)
+		chip_select = as->native_cs_for_gpio;
+	else
+		chip_select = spi->chip_select;
+
 	/* only deactivate *this* device; sometimes transfers to
 	 * another device may be active when this routine is called.
 	 */
 	mr = spi_readl(as, MR);
-	if (~SPI_BFEXT(PCS, mr) & (1 << spi->chip_select)) {
+	if (~SPI_BFEXT(PCS, mr) & (1 << chip_select)) {
 		mr = SPI_BFINS(PCS, 0xf, mr);
 		spi_writel(as, MR, mr);
 	}
@@ -815,6 +829,12 @@ static int atmel_spi_set_xfer_speed(struct atmel_spi *as,
 {
 	u32			scbr, csr;
 	unsigned long		bus_hz;
+	int chip_select;
+
+	if (spi->cs_gpiod)
+		chip_select = as->native_cs_for_gpio;
+	else
+		chip_select = spi->chip_select;
 
 	/* v1 chips start out at half the peripheral bus speed. */
 	bus_hz = as->spi_clk;
@@ -843,9 +863,9 @@ static int atmel_spi_set_xfer_speed(struct atmel_spi *as,
 			xfer->speed_hz, scbr, bus_hz);
 		return -EINVAL;
 	}
-	csr = spi_readl(as, CSR0 + 4 * spi->chip_select);
+	csr = spi_readl(as, CSR0 + 4 * chip_select);
 	csr = SPI_BFINS(SCBR, scbr, csr);
-	spi_writel(as, CSR0 + 4 * spi->chip_select, csr);
+	spi_writel(as, CSR0 + 4 * chip_select, csr);
 
 	return 0;
 }
@@ -1162,12 +1182,32 @@ static int atmel_word_delay_csr(struct spi_device *spi, struct atmel_spi *as)
 	return (as->spi_clk / 1000000 * value) >> 5;
 }
 
+static void initialize_native_cs_for_gpio(struct atmel_spi *as)
+{
+	int i;
+	struct spi_master *master = platform_get_drvdata(as->pdev);
+
+	if (!as->native_cs_free)
+		return; /* already initialized */
+
+	if (!master->cs_gpiods)
+		return; /* No CS GPIO */
+
+	for (i = 0; i < 4; i++)
+		if (master->cs_gpiods[i])
+			as->native_cs_free |= BIT(i);
+
+	if (as->native_cs_free)
+		as->native_cs_for_gpio = ffs(as->native_cs_free);
+}
+
 static int atmel_spi_setup(struct spi_device *spi)
 {
 	struct atmel_spi	*as;
 	struct atmel_spi_device	*asd;
 	u32			csr;
 	unsigned int		bits = spi->bits_per_word;
+	int chip_select;
 	int			word_delay_csr;
 
 	as = spi_master_get_devdata(spi->master);
@@ -1178,6 +1218,24 @@ static int atmel_spi_setup(struct spi_device *spi)
 		return -EINVAL;
 	}
 
+	/* Setup() is called during spi_register_controller(aka
+	 * spi_register_master) but after all membmers of the cs_gpiod
+	 * array have been filled, so we can looked for which native
+	 * CS will be free for using with GPIO
+	 */
+	initialize_native_cs_for_gpio(as);
+
+	if (spi->cs_gpiod && as->native_cs_free) {
+		dev_err(&spi->dev,
+			"No native CS available to support this GPIO CS\n");
+		return -EBUSY;
+	}
+
+	if (spi->cs_gpiod)
+		chip_select = as->native_cs_for_gpio;
+	else
+		chip_select = spi->chip_select;
+
 	csr = SPI_BF(BITS, bits - 8);
 	if (spi->mode & SPI_CPOL)
 		csr |= SPI_BIT(CPOL);
@@ -1213,7 +1271,7 @@ static int atmel_spi_setup(struct spi_device *spi)
 		bits, spi->mode, spi->chip_select, csr);
 
 	if (!atmel_spi_is_v2(as))
-		spi_writel(as, CSR0 + 4 * spi->chip_select, csr);
+		spi_writel(as, CSR0 + 4 * chip_select, csr);
 
 	return 0;
 }
-- 
2.23.0