lib: Implement hart hotplug

This patch adds support for hart hotplug in OpenSBI using a generic WFI
based approach. Hart hotplug can be achieved via SBI HSM extension which
allows supervisor mode software to start or stop any harts anytime.

Any platform wishes to implement platform specific hart hotplug must
implement both hart_start and hart_stop in addition to enable platform
feature SBI_PLATFORM_HAS_HART_HOTPLUG.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Reviewed-by: Anup Patel <anup.patel@wdc.com>

1 files changed, 43 insertions, 0 deletions

diff --git a/include/sbi/sbi_platform.h b/include/sbi/sbi_platform.h
index 16ee05c..462006e 100644
--- a/include/sbi/sbi_platform.h
+++ b/include/sbi/sbi_platform.h
@@ -135,6 +135,14 @@ struct sbi_platform_operations {
 	/** Exit platform timer for current HART */
 	void (*timer_exit)(void);
 
+	/** Bringup the given hart from previous stage **/
+	int (*hart_start)(u32 hartid, ulong saddr, ulong priv);
+	/**
+	 *  Stop the current hart from running. This call doesn't expect to
+	 *  return if success.
+	 */
+	int (*hart_stop)(void);
+
 	/** Reboot the platform */
 	int (*system_reboot)(u32 type);
 	/** Shutdown or poweroff the platform */
@@ -285,6 +293,41 @@ static inline u32 sbi_platform_hart_stack_size(const struct sbi_platform *plat)
 }
 
 /**
+ * Bringup a given hart from previous stage. Platform should implement this
+ * operation if they support a custom mechanism to start a hart. Otherwise,
+ * a generic WFI based approach will be used to start/stop a hart in OpenSBI.
+ *
+ * @param plat pointer to struct sbi_platform
+ * @param hartid Hart ID
+ * @param saddr  Physical address in supervisor mode for hart to jump after
+ *		 OpenSBI
+ * @param priv	 A private context data from the caller
+ *
+ * @return 0 if sucessful and negative error code on failure
+ */
+static inline int sbi_platform_hart_start(const struct sbi_platform *plat,
+					  u32 hartid, ulong saddr, ulong priv)
+{
+	if (plat && sbi_platform_ops(plat)->hart_start)
+		return sbi_platform_ops(plat)->hart_start(hartid, saddr, priv);
+	return SBI_ENOTSUPP;
+}
+
+/**
+ * Stop the current hart in OpenSBI.
+ *
+ * @param plat pointer to struct sbi_platform
+ *
+ * @return Negative error code on failure. It doesn't return on success.
+ */
+static inline int sbi_platform_hart_stop(const struct sbi_platform *plat)
+{
+	if (plat && sbi_platform_ops(plat)->hart_stop)
+		return sbi_platform_ops(plat)->hart_stop();
+	return SBI_ENOTSUPP;
+}
+
+/**
  * Early initialization for current HART
  *
  * @param plat pointer to struct sbi_platform