[PATCH] MIPS: add support for buggy MT7621S core detection

[Ilya Lipnitskiy]

Most MT7621 SoCs have 2 cores, which is detected and supported properly
by CPS.

Unfortunately, MT7621 SoC has a less common S variant with only one core.
On MT7621S, GCR_CONFIG still reports 2 cores, which leads to hangs when
starting SMP. CPULAUNCH registers can be used in that case to detect the
absence of the second core and override the GCR_CONFIG PCORES field.

Rework a long-standing OpenWrt patch to override the value of
mips_cps_numcores on single-core MT7621 systems.

Tested on a dual-core MT7621 device (Ubiquiti ER-X) and a single-core
MT7621 device (Netgear R6220).

Original 4.14 OpenWrt patch:
Link: https://git.openwrt.org/?p=openwrt/openwrt.git;a=commitdiff;h=4cdbc90a376dd0555201c1434a2081e055e9ceb7
Current 5.10 OpenWrt patch:
Link: https://git.openwrt.org/?p=openwrt/openwrt.git;a=blob;f=target/linux/ramips/patches-5.10/320-mt7621-core-detect-hack.patch;h=c63f0f4c1ec742e24d8480e80553863744b58f6a;hb=10267e17299806f9885d086147878f6c492cb904

Suggested-by: Felix Fietkau <nbd@xxxxxxxx>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@xxxxxxxxx>
---
 arch/mips/include/asm/bugs.h | 18 ++++++++++++++++++
 arch/mips/kernel/smp-cps.c   |  3 +++
 2 files changed, 21 insertions(+)

diff --git a/arch/mips/include/asm/bugs.h b/arch/mips/include/asm/bugs.h
index d72dc6e1cf3c..d32f0c4e61f7 100644
--- a/arch/mips/include/asm/bugs.h
+++ b/arch/mips/include/asm/bugs.h
@@ -16,6 +16,7 @@
 
 #include <asm/cpu.h>
 #include <asm/cpu-info.h>
+#include <asm/mips-boards/launch.h>
 
 extern int daddiu_bug;
 
@@ -50,4 +51,21 @@ static inline int r4k_daddiu_bug(void)
 	return daddiu_bug != 0;
 }
 
+static inline void cm_gcr_pcores_bug(unsigned int *ncores)
+{
+	struct cpulaunch *launch;
+
+	if (!IS_ENABLED(CONFIG_SOC_MT7621) || !ncores)
+		return;
+
+	/*
+	 * Ralink MT7621S SoC is single core, but GCR_CONFIG always reports 2 cores.
+	 * Use legacy amon method to detect if the second core is missing.
+	 */
+	launch = (struct cpulaunch *)CKSEG0ADDR(CPULAUNCH);
+	launch += 2; /* MT7621 has 2 VPEs per core */
+	if (!(launch->flags & LAUNCH_FREADY))
+		*ncores = 1;
+}
+
 #endif /* _ASM_BUGS_H */
diff --git a/arch/mips/kernel/smp-cps.c b/arch/mips/kernel/smp-cps.c
index bcd6a944b839..e1e9c11e8a7c 100644
--- a/arch/mips/kernel/smp-cps.c
+++ b/arch/mips/kernel/smp-cps.c
@@ -15,6 +15,7 @@
 #include <linux/irq.h>
 
 #include <asm/bcache.h>
+#include <asm/bugs.h>
 #include <asm/mips-cps.h>
 #include <asm/mips_mt.h>
 #include <asm/mipsregs.h>
@@ -60,6 +61,7 @@ static void __init cps_smp_setup(void)
 		pr_cont("{");
 
 		ncores = mips_cps_numcores(cl);
+		cm_gcr_pcores_bug(&ncores);
 		for (c = 0; c < ncores; c++) {
 			core_vpes = core_vpe_count(cl, c);
 
@@ -170,6 +172,7 @@ static void __init cps_prepare_cpus(unsigned int max_cpus)
 
 	/* Allocate core boot configuration structs */
 	ncores = mips_cps_numcores(0);
+	cm_gcr_pcores_bug(&ncores);
 	mips_cps_core_bootcfg = kcalloc(ncores, sizeof(*mips_cps_core_bootcfg),
 					GFP_KERNEL);
 	if (!mips_cps_core_bootcfg) {
-- 
2.31.1