lib: irqchip/plic: Add priority save/restore helpers

These can be used by platform code to save the PLIC priority state, if
it would otherwise be lost during non-retentive suspend. The platform
is responsible for allocating all necessary storage.

As a space optimization, store the saved priority values as 8-bit
integers, since that is large enough to hold any priority value on the
relevant platforms.

Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Samuel Holland <samuel@sholland.org>

include/sbi_utils/irqchip/plic.h

@@ -17,6 +17,11 @@ struct plic_data {
 	unsigned long num_src;
 };
 
+/* So far, priorities on all consumers of these functions fit in 8 bits. */
+void plic_priority_save(const struct plic_data *plic, u8 *priority);
+
+void plic_priority_restore(const struct plic_data *plic, const u8 *priority);
+
 void plic_context_save(const struct plic_data *plic, int context_id,
 		       u32 *enable, u32 *threshold);
 

lib/utils/irqchip/plic.c

@@ -22,6 +22,13 @@
 #define PLIC_CONTEXT_BASE 0x200000
 #define PLIC_CONTEXT_STRIDE 0x1000
 
+static u32 plic_get_priority(const struct plic_data *plic, u32 source)
+{
+	volatile void *plic_priority = (char *)plic->addr +
+			PLIC_PRIORITY_BASE + 4 * source;
+	return readl(plic_priority);
+}
+
 static void plic_set_priority(const struct plic_data *plic, u32 source, u32 val)
 {
 	volatile void *plic_priority = (char *)plic->addr +
@@ -29,6 +36,18 @@ static void plic_set_priority(const struct plic_data *plic, u32 source, u32 val)
 	writel(val, plic_priority);
 }
 
+void plic_priority_save(const struct plic_data *plic, u8 *priority)
+{
+	for (u32 i = 0; i < plic->num_src; i++)
+		priority[i] = plic_get_priority(plic, i);
+}
+
+void plic_priority_restore(const struct plic_data *plic, const u8 *priority)
+{
+	for (u32 i = 0; i < plic->num_src; i++)
+		plic_set_priority(plic, i, priority[i]);
+}
+
 static u32 plic_get_thresh(const struct plic_data *plic, u32 cntxid)
 {
 	volatile void *plic_thresh;