lib: utils/irqchip: Match against more specific compatible strings first

The T-HEAD C90x PLIC has some special quirks, such as the S-mode
delegation bit. OpenSBI currently handles this by checking the compatible
string in the device tree.

However, this matching is done in the order of the fdt_match array. So if
a device tree contains both strings, for example:

	compatible = "thead,c900-plic", "riscv,plic0";

Then OpenSBI will match against the generic "riscv,plic0" string, since
that appears first in the fdt_match array. This means it will fail to set
the S-mode delegation bit, and Linux will fail to boot. In some cases, it
is not possible to change the compatible string to just the T-HEAD PLIC,
as older versions of Linux only recognize the RISC-V compatible string.

This patch fixes that by moving the RISC-V string to the end, ensuring
that the more specific options get matched first.

Signed-off-by: Alex Studer <alex@studer.dev>
Reviewed-by: Anup Patel <anup@brainfault.org>

1 files changed, 7 insertions, 1 deletions

diff --git a/lib/utils/irqchip/fdt_irqchip_plic.c b/lib/utils/irqchip/fdt_irqchip_plic.c
index 494358d..59898d2 100644
--- a/lib/utils/irqchip/fdt_irqchip_plic.c
+++ b/lib/utils/irqchip/fdt_irqchip_plic.c
@@ -98,10 +98,16 @@ fail_free_data:
 
 static const struct fdt_match irqchip_plic_match[] = {
 	{ .compatible = "andestech,nceplic100" },
-	{ .compatible = "riscv,plic0" },
 	{ .compatible = "sifive,plic-1.0.0" },
 	{ .compatible = "thead,c900-plic",
 	  .data = (void *)(PLIC_FLAG_THEAD_DELEGATION | PLIC_FLAG_ENABLE_PM) },
+
+	/*
+	 * We keep the generic RISC-V PLIC at the end.
+	 * This ensures we match against more specific options first.
+	 * (This is important if the PLIC has quirks, like the T-HEAD PLIC.)
+	 */
+	{ .compatible = "riscv,plic0" },
 	{ /* sentinel */ }
 };