rp2040: Move chipid reading to bootrom.c

Rewrite chipid.c so that it contains just the USB and canbus id
manipulation code.  Move the low-level chipid reading to bootrom.c.

Also, introduce a new bootrom_reboot_usb_bootloader() function in
bootrom.c so that the main.c code does not need to know the specifics
of rebooting into the bootrom.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

src/rp2040/bootrom.c

@@ -6,7 +6,10 @@
 
 #include <stdint.h> // uint16_t, uint32_t, uintptr_t
 #include <string.h> // memcpy
+#include "board/irq.h" // irq_disable, irq_enable
 #include "compiler.h" // noinline, __section
+#include "hardware/structs/ioqspi.h" // ioqspi_hw
+#include "hardware/structs/ssi.h" // ssi_hw
 #include "internal.h" // _ramfunc
 
 #define ROM_TABLE_CODE(c1, c2) ((c1) | ((c2) << 8))
@@ -35,7 +38,7 @@ rom_func_lookup(uint32_t code)
   return fn(table, code);
 }
 
-void _ramfunc
+static void _ramfunc
 reset_to_usb_boot(uint32_t gpio_activity_pin_mask
                   , uint32_t disable_interface_mask)
 {
@@ -43,23 +46,129 @@ reset_to_usb_boot(uint32_t gpio_activity_pin_mask
   fn(gpio_activity_pin_mask, disable_interface_mask);
 }
 
-void _ramfunc
+static void _ramfunc
 connect_internal_flash(void)
 {
   void (*fn)(void) = rom_func_lookup(ROM_TABLE_CODE('I', 'F'));
   fn();
 }
 
-void _ramfunc
+static void _ramfunc
 flash_exit_xip(void)
 {
   void (*fn)(void) = rom_func_lookup(ROM_TABLE_CODE('E', 'X'));
   fn();
 }
 
-void _ramfunc
+static void _ramfunc
 flash_flush_cache(void)
 {
   void (*fn)(void) = rom_func_lookup(ROM_TABLE_CODE('F', 'C'));
   fn();
 }
+
+
+/****************************************************************
+ * Reboot to USB rom bootloader
+ ****************************************************************/
+
+void
+bootrom_reboot_usb_bootloader(void)
+{
+    reset_to_usb_boot(0, 0);
+}
+
+
+/****************************************************************
+ * Unique id reading
+ ****************************************************************/
+
+// Functions for reading out the flash chip ID. Adapted from the official
+// Pi SDK.
+
+static void _ramfunc
+flash_cs_force(int high)
+{
+    uint32_t field_val = high ?
+        IO_QSPI_GPIO_QSPI_SS_CTRL_OUTOVER_VALUE_HIGH :
+        IO_QSPI_GPIO_QSPI_SS_CTRL_OUTOVER_VALUE_LOW;
+    hw_write_masked(&ioqspi_hw->io[1].ctrl,
+        field_val << IO_QSPI_GPIO_QSPI_SS_CTRL_OUTOVER_LSB,
+        IO_QSPI_GPIO_QSPI_SS_CTRL_OUTOVER_BITS
+    );
+}
+
+// To re-enable XIP we need to call flash_enter_xip. It's available in the
+// bootrom, but that version is a generic one that works for most devices and
+// the tradeoff for that is enabling a low performance mode.
+// Instead we copy out the boot2 XIP enabling stage, and save it in RAM
+// so we can call it later on.
+
+#define BOOT2_SIZE 0x100
+
+static uint8_t boot2_copy[BOOT2_SIZE] __aligned(16);
+
+static void
+flash_enter_xip_prepare(void)
+{
+  void * volatile target = (void *)XIP_BASE; // Avoids warning
+  memcpy(boot2_copy, target, BOOT2_SIZE);
+  barrier();
+}
+
+static void _ramfunc
+flash_enter_xip_perform(void)
+{
+  ((void (*)(void))boot2_copy+1)();
+}
+
+#define FLASH_RUID_CMD         0x4B
+#define FLASH_RUID_DUMMY_BYTES 4
+#define FLASH_RUID_DATA_BYTES  8
+#define FLASH_RUID_TOTAL_BYTES (1+FLASH_RUID_DUMMY_BYTES+FLASH_RUID_DATA_BYTES)
+
+void _ramfunc
+bootrom_read_unique_id(uint8_t *out, uint32_t maxlen)
+{
+    uint8_t txbuf[FLASH_RUID_TOTAL_BYTES] = {0};
+    uint8_t rxbuf[FLASH_RUID_TOTAL_BYTES] = {0};
+
+    uint8_t *txptr = txbuf;
+    uint8_t *rxptr = rxbuf;
+
+    int tx_remaining = FLASH_RUID_TOTAL_BYTES;
+    int rx_remaining = FLASH_RUID_TOTAL_BYTES;
+
+    txbuf[0] = FLASH_RUID_CMD;
+
+    // Set up flash so we can work with it without XIP getting in the way
+    flash_enter_xip_prepare();
+    irq_disable();
+    barrier();
+    connect_internal_flash();
+    flash_exit_xip();
+    flash_cs_force(0);
+
+    while (tx_remaining || rx_remaining) {
+        uint32_t flags = ssi_hw->sr;
+        int can_put = !!(flags & SSI_SR_TFNF_BITS);
+        int can_get = !!(flags & SSI_SR_RFNE_BITS);
+        if (can_put && tx_remaining) {
+            ssi_hw->dr0 = *txptr++;
+            tx_remaining--;
+        }
+        if (can_get && rx_remaining) {
+            *rxptr++ = (uint8_t)ssi_hw->dr0;
+            --rx_remaining;
+        }
+    }
+
+    // Restore XIP
+    flash_cs_force(1);
+    flash_flush_cache();
+    flash_enter_xip_perform();
+    barrier();
+    irq_enable();
+
+    memcpy(out, rxbuf+1+FLASH_RUID_DUMMY_BYTES, FLASH_RUID_DATA_BYTES);
+}