[PATCH] powerpc/prom: Add CPU info to hardware description string later

[Nathan Lynch via B4 Relay]

From: Nathan Lynch <nathanl at linux.ibm.com>

cur_cpu_spec->cpu_name is appended to ppc_hw_desc before cur_cpu_spec
has taken on its final value. This is illustrated on pseries by
comparing the CPU name as reported at boot ("POWER8E (raw)") to the
contents of /proc/cpuinfo ("POWER8 (architected)"):

  $ dmesg | grep Hardware
  Hardware name: IBM,8408-E8E POWER8E (raw) 0x4b0201 0xf000004 \
    of:IBM,FW860.50 (SV860_146) hv:phyp pSeries

  $ grep -m 1 ^cpu /proc/cpuinfo
  cpu             : POWER8 (architected), altivec supported

Some 44x models would appear to be affected as well; see
identical_pvr_fixup().

This results in incorrect CPU information in stack dumps --
ppc_hw_desc is an input to dump_stack_set_arch_desc().

Delay gathering the CPU name until after all potential calls to
identify_cpu().

Signed-off-by: Nathan Lynch <nathanl at linux.ibm.com>
Fixes: bd649d40e0f2 ("powerpc: Add PVR & CPU name to hardware description")
---
Originally sent as part of a RFC series to update the hardware
description at runtime for live migration:

https://lore.kernel.org/linuxppc-dev/20240118-update-dump-stack-arch-str-v1-0-5c0f98d017b5@linux.ibm.com/

Sending this separately as a standalone fix before I take that effort
up again.
---
 arch/powerpc/kernel/prom.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 60819751e55e..0be07ed407c7 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -331,6 +331,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 					  void *data)
 {
 	const char *type = of_get_flat_dt_prop(node, "device_type", NULL);
+	const __be32 *cpu_version = NULL;
 	const __be32 *prop;
 	const __be32 *intserv;
 	int i, nthreads;
@@ -420,7 +421,7 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 		prop = of_get_flat_dt_prop(node, "cpu-version", NULL);
 		if (prop && (be32_to_cpup(prop) & 0xff000000) == 0x0f000000) {
 			identify_cpu(0, be32_to_cpup(prop));
-			seq_buf_printf(&ppc_hw_desc, "0x%04x ", be32_to_cpup(prop));
+			cpu_version = prop;
 		}
 
 		check_cpu_feature_properties(node);
@@ -431,6 +432,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	}
 
 	identical_pvr_fixup(node);
+
+	// We can now add the CPU name & PVR to the hardware description
+	seq_buf_printf(&ppc_hw_desc, "%s 0x%04lx ", cur_cpu_spec->cpu_name, mfspr(SPRN_PVR));
+	if (cpu_version)
+		seq_buf_printf(&ppc_hw_desc, "0x%04x ", be32_to_cpup(cpu_version));
+
 	init_mmu_slb_size(node);
 
 #ifdef CONFIG_PPC64
@@ -881,9 +888,6 @@ void __init early_init_devtree(void *params)
 
 	dt_cpu_ftrs_scan();
 
-	// We can now add the CPU name & PVR to the hardware description
-	seq_buf_printf(&ppc_hw_desc, "%s 0x%04lx ", cur_cpu_spec->cpu_name, mfspr(SPRN_PVR));
-
 	/* Retrieve CPU related informations from the flat tree
 	 * (altivec support, boot CPU ID, ...)
 	 */

---
base-commit: be2fc65d66e0406cc9d39d40becaecdf4ee765f3
change-id: 20240603-fix-cpu-hwdesc-1dc055b3f93f

Best regards,
-- 
Nathan Lynch <nathanl at linux.ibm.com>