powerpc: Add hardware description string

Create a hardware description string, which we will use to record
various details of the hardware platform we are running on.

Print the accumulated description at boot, and use it to set the generic
description which is printed in oopses.

To begin with add ppc_md.name, aka the "machine description".

Example output at boot with the full series applied:

  Linux version 6.0.0-rc2-gcc-11.1.0-00199-g893f9007a5ce-dirty (michael@alpine1-p1) (powerpc64-linux-gcc (GCC) 11.1.0, GNU ld (GNU Binutils) 2.36.1) #844 SMP Thu Sep 29 22:29:53 AEST 2022
  Hardware name: IBM pSeries (emulated by qemu) POWER9 (raw) 0x4e1200 0xf000005 of:SLOF,git-5b4c5a pSeries
  printk: bootconsole [udbg0] enabled
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20220930082709.55830-1-mpe@ellerman.id.au

arch/powerpc/include/asm/setup.h

@@ -88,6 +88,8 @@ unsigned long __init prom_init(unsigned long r3, unsigned long r4,
 			       unsigned long pp, unsigned long r6,
 			       unsigned long r7, unsigned long kbase);
 
+extern struct seq_buf ppc_hw_desc;
+
 #endif /* !__ASSEMBLY__ */
 
 #endif	/* _ASM_POWERPC_SETUP_H */

arch/powerpc/kernel/setup-common.c

@@ -18,6 +18,7 @@
 #include <linux/delay.h>
 #include <linux/initrd.h>
 #include <linux/platform_device.h>
+#include <linux/printk.h>
 #include <linux/seq_file.h>
 #include <linux/ioport.h>
 #include <linux/console.h>
@@ -25,6 +26,7 @@
 #include <linux/root_dev.h>
 #include <linux/cpu.h>
 #include <linux/unistd.h>
+#include <linux/seq_buf.h>
 #include <linux/serial.h>
 #include <linux/serial_8250.h>
 #include <linux/percpu.h>
@@ -588,6 +590,15 @@ static __init int add_pcspkr(void)
 device_initcall(add_pcspkr);
 #endif	/* CONFIG_PCSPKR_PLATFORM */
 
+static char ppc_hw_desc_buf[128] __initdata;
+
+struct seq_buf ppc_hw_desc __initdata = {
+	.buffer = ppc_hw_desc_buf,
+	.size = sizeof(ppc_hw_desc_buf),
+	.len = 0,
+	.readpos = 0,
+};
+
 static __init void probe_machine(void)
 {
 	extern struct machdep_calls __machine_desc_start;
@@ -628,7 +639,13 @@ static __init void probe_machine(void)
 		for (;;);
 	}
 
-	printk(KERN_INFO "Using %s machine description\n", ppc_md.name);
+	// Append the machine name to other info we've gathered
+	seq_buf_puts(&ppc_hw_desc, ppc_md.name);
+
+	// Set the generic hardware description shown in oopses
+	dump_stack_set_arch_desc(ppc_hw_desc.buffer);
+
+	pr_info("Hardware name: %s\n", ppc_hw_desc.buffer);
 }
 
 /* Match a class of boards, not a specific device configuration. */