spi: sh-msiof: Add support for R-Car H2 and M2

Add support for the MSIOF variant in the R-Car H2 (r8a7790) and M2
(r8a7791) SoCs.

Binding documentation:
  - Add future-proof "renesas,msiof-<soctype>" compatible values,
  - The default for "renesas,rx-fifo-size" is 256 on R-Car H2 and M2,
  - "renesas,tx-fifo-size" and "renesas,rx-fifo-size" are deprecated for
    soctype-specific bindings,
  - Add example bindings.

Implementation:
  - MSIOF on R-Car H2 and M2 requires the transmission of dummy data if
    data is being received only (cfr. "Set SICTR.TSCKE to 1" and "Write
    dummy transmission data to SITFDR" in paragraph "Transmit and Receive
    Procedures" of the Hardware User's Manual).
  - As RX depends on TX, MSIOF on R-Car H2 and M2 also lacks the RSCR
    register (Receive Clock Select Register), and some bits in the RMDR1
    (Receive Mode Register 1) and TMDR2 (Transmit Mode Register 2)
    registers.
  - Use the recently introduced SPI_MASTER_MUST_TX flag to enable support
    for dummy transmission in the SPI core, and to differentiate from other
    MSIOF implementations in code paths that need this.
  - New DT compatible values ("renesas,msiof-r8a7790" and
    "renesas,msiof-r8a7791") are added, as well as new platform device
    names ("spi_r8a7790_msiof" and "spi_r8a7791_msiof").
  - The default RX FIFO size is 256 words on R-Car H2 and M2.

This is loosely based on a set of patches from Takashi Yoshii
<takasi-y@ops.dti.ne.jp>.

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Mark Brown <broonie@linaro.org>

Documentation/devicetree/bindings/spi/sh-msiof.txt

@@ -1,8 +1,13 @@
 Renesas MSIOF spi controller
 
 Required properties:
-- compatible           : "renesas,sh-msiof" for SuperH, or
+- compatible           : "renesas,msiof-<soctype>" for SoCs,
+			 "renesas,sh-msiof" for SuperH, or
 			 "renesas,sh-mobile-msiof" for SH Mobile series.
+			 Examples with soctypes are:
+			 "renesas,msiof-sh7724" (SH)
+			 "renesas,msiof-r8a7790" (R-Car H2)
+			 "renesas,msiof-r8a7791" (R-Car M2)
 - reg                  : Offset and length of the register set for the device
 - interrupt-parent     : The phandle for the interrupt controller that
 			 services interrupts for this device
@@ -13,10 +18,24 @@ Required properties:
 Optional properties:
 - clocks               : Must contain a reference to the functional clock.
 - num-cs               : Total number of chip-selects (default is 1)
+
+Optional properties, deprecated for soctype-specific bindings:
 - renesas,tx-fifo-size : Overrides the default tx fifo size given in words
 			 (default is 64)
 - renesas,rx-fifo-size : Overrides the default rx fifo size given in words
-			 (default is 64)
+			 (default is 64, or 256 on R-Car H2 and M2)
 
 Pinctrl properties might be needed, too.  See
 Documentation/devicetree/bindings/pinctrl/renesas,*.
+
+Example:
+
+	msiof0: spi@e6e20000 {
+		compatible = "renesas,msiof-r8a7791";
+		reg = <0 0xe6e20000 0 0x0064>;
+		interrupts = <0 156 IRQ_TYPE_LEVEL_HIGH>;
+		clocks = <&mstp0_clks R8A7791_CLK_MSIOF0>;
+		#address-cells = <1>;
+		#size-cells = <0>;
+		status = "disabled";
+	};

drivers/spi/spi-sh-msiof.c

@@ -35,6 +35,7 @@
 struct sh_msiof_chipdata {
 	u16 tx_fifo_size;
 	u16 rx_fifo_size;
+	u16 master_flags;
 };
 
 struct sh_msiof_spi_priv {
@@ -215,7 +216,8 @@ static void sh_msiof_spi_set_clk_regs(struct sh_msiof_spi_priv *p,
 	k = min_t(int, k, ARRAY_SIZE(sh_msiof_spi_clk_table) - 1);
 
 	sh_msiof_write(p, TSCR, sh_msiof_spi_clk_table[k].scr);
-	sh_msiof_write(p, RSCR, sh_msiof_spi_clk_table[k].scr);
+	if (!(p->chipdata->master_flags & SPI_MASTER_MUST_TX))
+		sh_msiof_write(p, RSCR, sh_msiof_spi_clk_table[k].scr);
 }
 
 static void sh_msiof_spi_set_pin_regs(struct sh_msiof_spi_priv *p,
@@ -238,6 +240,10 @@ static void sh_msiof_spi_set_pin_regs(struct sh_msiof_spi_priv *p,
 	tmp |= !cs_high << MDR1_SYNCAC_SHIFT;
 	tmp |= lsb_first << MDR1_BITLSB_SHIFT;
 	sh_msiof_write(p, TMDR1, tmp | MDR1_TRMD | TMDR1_PCON);
+	if (p->chipdata->master_flags & SPI_MASTER_MUST_TX) {
+		/* These bits are reserved if RX needs TX */
+		tmp &= ~0x0000ffff;
+	}
 	sh_msiof_write(p, RMDR1, tmp);
 
 	tmp = 0;
@@ -258,7 +264,7 @@ static void sh_msiof_spi_set_mode_regs(struct sh_msiof_spi_priv *p,
 {
 	u32 dr2 = MDR2_BITLEN1(bits) | MDR2_WDLEN1(words);
 
-	if (tx_buf)
+	if (tx_buf || (p->chipdata->master_flags & SPI_MASTER_MUST_TX))
 		sh_msiof_write(p, TMDR2, dr2);
 	else
 		sh_msiof_write(p, TMDR2, dr2 | MDR2_GRPMASK1);
@@ -666,11 +672,20 @@ static u32 sh_msiof_spi_txrx_word(struct spi_device *spi, unsigned nsecs,
 static const struct sh_msiof_chipdata sh_data = {
 	.tx_fifo_size = 64,
 	.rx_fifo_size = 64,
+	.master_flags = 0,
+};
+
+static const struct sh_msiof_chipdata r8a779x_data = {
+	.tx_fifo_size = 64,
+	.rx_fifo_size = 256,
+	.master_flags = SPI_MASTER_MUST_TX,
 };
 
 static const struct of_device_id sh_msiof_match[] = {
 	{ .compatible = "renesas,sh-msiof",        .data = &sh_data },
 	{ .compatible = "renesas,sh-mobile-msiof", .data = &sh_data },
+	{ .compatible = "renesas,msiof-r8a7790",   .data = &r8a779x_data },
+	{ .compatible = "renesas,msiof-r8a7791",   .data = &r8a779x_data },
 	{},
 };
 MODULE_DEVICE_TABLE(of, sh_msiof_match);
@@ -790,7 +805,7 @@ static int sh_msiof_spi_probe(struct platform_device *pdev)
 	/* init master and bitbang code */
 	master->mode_bits = SPI_CPOL | SPI_CPHA | SPI_CS_HIGH;
 	master->mode_bits |= SPI_LSB_FIRST | SPI_3WIRE;
-	master->flags = 0;
+	master->flags = p->chipdata->master_flags;
 	master->bus_num = pdev->id;
 	master->dev.of_node = pdev->dev.of_node;
 	master->num_chipselect = p->info->num_chipselect;
@@ -833,6 +848,8 @@ static int sh_msiof_spi_remove(struct platform_device *pdev)
 
 static struct platform_device_id spi_driver_ids[] = {
 	{ "spi_sh_msiof",	(kernel_ulong_t)&sh_data },
+	{ "spi_r8a7790_msiof",	(kernel_ulong_t)&r8a779x_data },
+	{ "spi_r8a7791_msiof",	(kernel_ulong_t)&r8a779x_data },
 	{},
 };
 MODULE_DEVICE_TABLE(platform, spi_driver_ids);