[PATCH] xen/rpi4: implement watchdog-based reset

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

Touching the watchdog is required to be able to reboot the board.

The implementation is based on
drivers/watchdog/bcm2835_wdt.c:__bcm2835_restart in Linux.

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
---
 xen/arch/arm/platforms/brcm-raspberry-pi.c | 60 ++++++++++++++++++++++
 1 file changed, 60 insertions(+)

diff --git a/xen/arch/arm/platforms/brcm-raspberry-pi.c 
b/xen/arch/arm/platforms/brcm-raspberry-pi.c
index f5ae58a7d5..0214ae2b3c 100644
--- a/xen/arch/arm/platforms/brcm-raspberry-pi.c
+++ b/xen/arch/arm/platforms/brcm-raspberry-pi.c
@@ -18,6 +18,10 @@
  */
 
 #include <asm/platform.h>
+#include <xen/delay.h>
+#include <xen/mm.h>
+#include <xen/vmap.h>
+#include <asm/io.h>
 
 static const char *const rpi4_dt_compat[] __initconst =
 {
@@ -37,12 +41,68 @@ static const struct dt_device_match rpi4_blacklist_dev[] 
__initconst =
      * The aux peripheral also shares a page with the aux UART.
      */
     DT_MATCH_COMPATIBLE("brcm,bcm2835-aux"),
+    /* Special device used for rebooting */
+    DT_MATCH_COMPATIBLE("brcm,bcm2835-pm"),
     { /* sentinel */ },
 };
 
+
+#define PM_PASSWORD         0x5a000000
+#define PM_RSTC             0x1c
+#define PM_WDOG             0x24
+#define PM_RSTC_WRCFG_FULL_RESET    0x00000020
+#define PM_RSTC_WRCFG_CLR           0xffffffcf
+
+static void __iomem *rpi4_map_watchdog(void)
+{
+    void __iomem *base;
+    struct dt_device_node *node;
+    paddr_t start, len;
+    int ret;
+
+    node = dt_find_compatible_node(NULL, NULL, "brcm,bcm2835-pm");
+    if ( !node )
+        return NULL;
+
+    ret = dt_device_get_address(node, 0, &start, &len);
+    if ( ret )
+    {
+        dprintk(XENLOG_ERR, "Cannot read watchdog register address\n");
+        return NULL;
+    }
+
+    base = ioremap_nocache(start & PAGE_MASK, PAGE_SIZE);
+    if ( !base )
+    {
+        dprintk(XENLOG_ERR, "Unable to map watchdog register!\n");
+        return NULL;
+    }
+
+    return base;
+}
+
+static void rpi4_reset(void)
+{
+    u32 val;
+    void __iomem *base = rpi4_map_watchdog();
+    if ( !base )
+        return;
+
+    /* use a timeout of 10 ticks (~150us) */
+    writel(10 | PM_PASSWORD, base + PM_WDOG);
+    val = readl(base + PM_RSTC);
+    val &= PM_RSTC_WRCFG_CLR;
+    val |= PM_PASSWORD | PM_RSTC_WRCFG_FULL_RESET;
+    writel(val, base + PM_RSTC);
+
+    /* No sleeping, possibly atomic. */
+    mdelay(1);
+}
+
 PLATFORM_START(rpi4, "Raspberry Pi 4")
     .compatible     = rpi4_dt_compat,
     .blacklist_dev  = rpi4_blacklist_dev,
+    .reset = rpi4_reset,
     .dma_bitsize    = 30,
 PLATFORM_END
 
-- 
2.17.1