Added support for manual CS control

This serprog spec addition added support for selecting the
CS mode for SPI_OP commands:

https://review.coreboot.org/c/flashrom/+/81428

This commit adds support for the 0x18 S_CS_MODE command.

Author: funkeleinhorn

main.c

@@ -41,7 +41,8 @@
   (1 << S_CMD_S_SPI_FREQ)  | \
   (1 << S_CMD_S_PIN_STATE) | \
   (1 << S_CMD_S_SPI_CS)    | \
-  (1 << S_CMD_S_SPI_MODE)    \
+  (1 << S_CMD_S_SPI_MODE)  | \
+  (1 << S_CMD_S_CS_MODE)     \
 )
 
 enum spi_mode {
@@ -52,6 +53,15 @@ enum spi_mode {
 
 enum spi_mode current_spi_mode = SPI_MODE_HALF_DUPLEX;
 
+enum cs_mode {
+    CS_MODE_AUTO = 0,
+    CS_MODE_SELECTED = 1,
+    CS_MODE_DESELECTED = 2,
+    CS_MODE_MAX = CS_MODE_DESELECTED,
+};
+
+enum cs_mode current_cs_mode = CS_MODE_AUTO;
+
 uint active_cs_pin = 0;
 #define NUM_CS_AVAILABLE 4 // Number of usable chip selects
 uint8_t cs_pins[NUM_CS_AVAILABLE] = { PIN_CS_0, PIN_CS_1, PIN_CS_2, PIN_CS_3 };
@@ -200,7 +210,9 @@ void process(const pio_spi_inst_t *spi, int command) {
                 uint32_t wlen = getu24();
                 uint32_t rlen = getu24();
 
-                cs_select(active_cs_pin);
+                if (current_cs_mode == CS_MODE_AUTO) {
+                    cs_select(active_cs_pin);
+                }
                 switch (current_spi_mode) {
                 case SPI_MODE_HALF_DUPLEX:
                     spi_half_duplex(spi, wlen, rlen);
@@ -211,7 +223,9 @@ void process(const pio_spi_inst_t *spi, int command) {
                 default:
                     break;
                 }
-                cs_deselect(active_cs_pin);
+                if (current_spi_mode == CS_MODE_AUTO) {
+                    cs_deselect(active_cs_pin);
+                }
             }
             break;
         case S_CMD_S_SPI_FREQ:
@@ -253,6 +267,27 @@ void process(const pio_spi_inst_t *spi, int command) {
                 }
                 break;
             }
+        case S_CMD_S_CS_MODE:
+            {
+                uint8_t cs_mode = getchar();
+                switch (cs_mode) {
+                    case CS_MODE_AUTO:
+                    case CS_MODE_DESELECTED:
+                        cs_deselect(active_cs_pin);
+                        current_cs_mode = cs_mode;
+                        putchar(S_ACK);
+                        break;
+                    case CS_MODE_SELECTED:
+                        cs_select(active_cs_pin);
+                        current_cs_mode = cs_mode;
+                        putchar(S_ACK);
+                        break;
+                    default:
+                        putchar(S_NAK);
+                        break;
+                }
+                break;
+            }
         default:
             putchar(S_NAK);
     }

spi.h

@@ -25,3 +25,4 @@
 #define S_CMD_S_PIN_STATE	0x15	/* Enable/disable output drivers		*/
 #define S_CMD_S_SPI_CS		0x16	/* Set SPI chip select to use			*/
 #define S_CMD_S_SPI_MODE	0x17	/* Sets the spi mode used by S_CMD_O_SPIOP      */
+#define S_CMD_S_CS_MODE 	0x18	/* Sets the way the CS is controlled  */