[PATCH v3 3/7] riscv: Use a valid bit to ignore already-pending IPIs

[Sean Anderson]

Some IPIs may already be pending when U-Boot is started. This could be a
problem if a secondary hart tries to handle an IPI before the boot hart has
initialized the IPI device.

To be specific, the Kendryte K210 ROM-based bootloader does not clear IPIs
before passing control to U-Boot. Without this patch, the secondary hart
jumps to address 0x0 as soon as it enters secondary_hart_loop, and then
hangs in its trap handler.

This commit introduces a valid bit so secondary harts know when and IPI
originates from U-Boot, and it is safe to use the IPI API. The valid bit is
initialized to 0 by board_init_f_init_reserve. Before this, secondary harts
wait in wait_for_gd_init.

Signed-off-by: Sean Anderson <seanga2 at gmail.com>
Reviewed-by: Bin Meng <bin.meng at windriver.com>
Reviewed-by: Rick Chen <rick at andestech.com>
Reviewed-by: Leo Liang <ycliang at andestech.com>
---

(no changes since v2)

Changes in v2:
- Use a valid bit instead of addr to validate IPIs

 arch/riscv/include/asm/smp.h |  7 +++++++
 arch/riscv/lib/smp.c         | 16 ++++++++++++++--
 2 files changed, 21 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
index 1b428856b2..2dae0800ce 100644
--- a/arch/riscv/include/asm/smp.h
+++ b/arch/riscv/include/asm/smp.h
@@ -18,14 +18,21 @@
  * IPI data structure. The hart ID is inserted by the hart handling the IPI and
  * calling the function.
  *
+ * @valid is used to determine whether a sent IPI originated from U-Boot. It is
+ * initialized to zero by board_init_f_alloc_reserve. When U-Boot sends its
+ * first IPI, it is set to 1. This prevents already-pending IPIs not sent by
+ * U-Boot from being taken.
+ *
  * @addr: Address of function
  * @arg0: First argument of function
  * @arg1: Second argument of function
+ * @valid: Whether this IPI is valid
  */
 struct ipi_data {
 	ulong addr;
 	ulong arg0;
 	ulong arg1;
+	unsigned int valid;
 };
 
 /**
diff --git a/arch/riscv/lib/smp.c b/arch/riscv/lib/smp.c
index ab6d8bd7fa..8f33ce1fe3 100644
--- a/arch/riscv/lib/smp.c
+++ b/arch/riscv/lib/smp.c
@@ -54,7 +54,13 @@ static int send_ipi_many(struct ipi_data *ipi, int wait)
 		gd->arch.ipi[reg].arg0 = ipi->arg0;
 		gd->arch.ipi[reg].arg1 = ipi->arg1;
 
-		__smp_mb();
+		/*
+		 * Ensure valid only becomes set when the IPI parameters are
+		 * set. An IPI may already be pending on other harts, so we
+		 * need a way to signal that the IPI device has been
+		 * initialized, and that it is ok to call the function.
+		 */
+		__smp_store_release(&gd->arch.ipi[reg].valid, 1);
 
 		ret = riscv_send_ipi(reg);
 		if (ret) {
@@ -83,7 +89,13 @@ void handle_ipi(ulong hart)
 	if (hart >= CONFIG_NR_CPUS)
 		return;
 
-	__smp_mb();
+	/*
+	 * If valid is not set, then U-Boot has not requested the IPI. The
+	 * IPI device may not be initialized, so all we can do is wait for
+	 * U-Boot to initialize it and send an IPI
+	 */
+	if (!__smp_load_acquire(&gd->arch.ipi[hart].valid))
+		return;
 
 	smp_function = (void (*)(ulong, ulong, ulong))gd->arch.ipi[hart].addr;
 	invalidate_icache_all();
-- 
2.28.0