drivers: fpga: simplify load mode selection of iCE40

Replace the enum for load modes for the iCE40 with a boolean flag,
as there are only two options:
- SPI: default, which should be used whenever possible
- GPIO bitbang: workarorund, in case a low-end microcontroller is used

Signed-off-by: Benedikt Schmidt <[email protected]>

drivers/fpga/fpga_ice40.c

@@ -42,14 +42,7 @@
  * achieve the minimum 1 MHz clock rate for loading the iCE40 bistream. So
  * in order to bitbang on lower-end microcontrollers, we actually require
  * direct register access to the set and clear registers.
- *
- * With that, this driver is left with 2 possible modes of operation which
- * are:
- * - FPGA_ICE40_LOAD_MODE_SPI (for higher-end microcontrollers)
- * - FPGA_ICE40_LOAD_MODE_GPIO (for lower-end microcontrollers)
  */
-#define FPGA_ICE40_LOAD_MODE_SPI  0
-#define FPGA_ICE40_LOAD_MODE_GPIO 1
 
 /*
  * Values in Hz, intentionally to be comparable with the spi-max-frequency
@@ -111,7 +104,7 @@ static void fpga_ice40_crc_to_str(uint32_t crc, char *s)
 
 /*
  * This is a calibrated delay loop used to achieve a 1 MHz SPI_CLK frequency
- * with FPGA_ICE40_LOAD_MODE_GPIO. It is used both in fpga_ice40_send_clocks()
+ * with the bitbang mode. It is used both in fpga_ice40_send_clocks()
  * and fpga_ice40_spi_send_data().
  *
  * Calibration is achieved via the mhz_delay_count device tree parameter. See
@@ -573,12 +566,8 @@ static int fpga_ice40_init(const struct device *dev)
 
 #define FPGA_ICE40_GPIO_PINS(inst, name) (volatile gpio_port_pins_t *)DT_INST_PROP_OR(inst, name, 0)
 
-#define FPGA_ICE40_LOAD_MODE(inst) DT_INST_PROP(inst, load_mode)
 #define FPGA_ICE40_LOAD_FUNC(inst)                                                                 \
-	(FPGA_ICE40_LOAD_MODE(inst) == FPGA_ICE40_LOAD_MODE_SPI                                    \
-		 ? fpga_ice40_load_spi                                                             \
-		 : (FPGA_ICE40_LOAD_MODE(inst) == FPGA_ICE40_LOAD_MODE_GPIO ? fpga_ice40_load_gpio \
-									    : NULL))
+	(DT_INST_PROP(inst, load_mode_bitbang) ? fpga_ice40_load_gpio : fpga_ice40_load_spi)
 
 #ifdef CONFIG_PINCTRL
 #define FPGA_ICE40_PINCTRL_CONFIG(inst) .pincfg = PINCTRL_DT_DEV_CONFIG_GET(DT_INST_PARENT(inst)),
@@ -589,8 +578,6 @@ static int fpga_ice40_init(const struct device *dev)
 #endif
 
 #define FPGA_ICE40_DEFINE(inst)                                                                    \
-	BUILD_ASSERT(FPGA_ICE40_LOAD_MODE(inst) == FPGA_ICE40_LOAD_MODE_SPI ||                     \
-		     FPGA_ICE40_LOAD_MODE(inst) == FPGA_ICE40_LOAD_MODE_GPIO);                     \
 	BUILD_ASSERT(FPGA_ICE40_BUS_FREQ(inst) >= FPGA_ICE40_SPI_HZ_MIN);                          \
 	BUILD_ASSERT(FPGA_ICE40_BUS_FREQ(inst) <= FPGA_ICE40_SPI_HZ_MAX);                          \
 	BUILD_ASSERT(FPGA_ICE40_CONFIG_DELAY_US(inst) >= FPGA_ICE40_CONFIG_DELAY_US_MIN);          \

dts/bindings/fpga/lattice,ice40-fpga.yaml

@@ -8,20 +8,14 @@ compatible: "lattice,ice40-fpga"
 include: spi-device.yaml
 
 properties:
-  load-mode:
-    type: int
-    required: true
+  load-mode-bitbang:
+    type: boolean
     description: |
-      Configure the method used to load the bitstream.
-      The bitstream may be loaded via 2 separate methods:
-      0 := load the FPGA via SPI transfer
-      1 := load the FPGA via bit-banged GPIO
-      Option 0 may be suitable for some high-end microcontrollers.
-      Option 1 is suitable for low-end microcontrollers. This option
-      requires clk-gpios, pico-gpios, gpios-set-reg, and gpios-clear-reg
-      to be defined.
-      Example usage:
-      load-mode = <0>;
+      Select the bitbang mode for loading the bitstream into the FPGA.
+      This is a workaround to meet the timing requirements fo the iCE40
+      on low-end microcontrollers.
+      This option requires clk-gpios, pico-gpios, gpios-set-reg, and
+      gpios-clear-reg to be defined.
   cdone-gpios:
     type: phandle-array
     required: true

tests/drivers/build_all/fpga/spi.dtsi

@@ -13,7 +13,7 @@ test_spi_fpga_ice40_gpio: ice40@0 {
 	reg = <0>;
 	spi-max-frequency = <1000000>;
 
-	load-mode = <0>;
+	load-mode-bitbang;
 	cdone-gpios = <&test_gpio 0 0>;
 	creset-gpios = <&test_gpio 0 0>;
 	config-delay-us = <3900>;
@@ -26,7 +26,6 @@ test_spi_fpga_ice40_spi: ice40@1 {
 	reg = <1>;
 	spi-max-frequency = <1000000>;
 
-	load-mode = <1>;
 	cdone-gpios = <&test_gpio 0 0>;
 	creset-gpios = <&test_gpio 0 0>;
 	clk-gpios = <&test_gpio 0 0>;