openrisc: Implement fixmap to fix earlycon

With commit 53c98e3 ("openrisc: mm: remove unneeded early ioremap
code") it was commented that early ioremap was not used in OpenRISC.  I
acked this but was wrong, earlycon was using it.  Earlycon setup now
fails with the below trace:

    Kernel command line: earlycon
    ------------[ cut here ]------------
    WARNING: CPU: 0 PID: 0 at mm/ioremap.c:23
    generic_ioremap_prot+0x118/0x130
    Modules linked in:
    CPU: 0 UID: 0 PID: 0 Comm: swapper Not tainted
    6.11.0-rc5-00001-gce02fd891c38-dirty torvalds#141
    Call trace:
    [<(ptrval)>] dump_stack_lvl+0x7c/0x9c
    [<(ptrval)>] dump_stack+0x1c/0x2c
    [<(ptrval)>] __warn+0xb4/0x108
    [<(ptrval)>] ? generic_ioremap_prot+0x118/0x130
    [<(ptrval)>] warn_slowpath_fmt+0x60/0x98
    [<(ptrval)>] generic_ioremap_prot+0x118/0x130
    [<(ptrval)>] ioremap_prot+0x20/0x30
    [<(ptrval)>] of_setup_earlycon+0xd4/0x2e0
    [<(ptrval)>] early_init_dt_scan_chosen_stdout+0x18c/0x1c8
    [<(ptrval)>] param_setup_earlycon+0x3c/0x60
    [<(ptrval)>] do_early_param+0xb0/0x118
    [<(ptrval)>] parse_args+0x184/0x4b8
    [<(ptrval)>] ? start_kernel+0x0/0x78c
    [<(ptrval)>] parse_early_options+0x40/0x50
    [<(ptrval)>] ? do_early_param+0x0/0x118
    [<(ptrval)>] parse_early_param+0x48/0x68
    [<(ptrval)>] ? start_kernel+0x318/0x78c
    [<(ptrval)>] ? start_kernel+0x0/0x78c
    ---[ end trace 0000000000000000 ]---

To fix this we could either implement early_ioremap again or implement
fixmap.  In this patch we choose the later option of implementing basic
fixmap support.

While fixing this we also remove the old FIX_IOREMAP slots that were
used by early ioremap code.  That code was also removed by commit
53c98e3 ("openrisc: mm: remove unneeded early ioremap code") but
these definitions were not cleaned up.

Fixes: 53c98e3 ("openrisc: mm: remove unneeded early ioremap code")
Signed-off-by: Stafford Horne <shorne@gmail.com>

arch/openrisc/Kconfig

@@ -65,6 +65,9 @@ config STACKTRACE_SUPPORT
 config LOCKDEP_SUPPORT
 	def_bool  y
 
+config FIX_EARLYCON_MEM
+	def_bool y
+
 menu "Processor type and features"
 
 choice

arch/openrisc/include/asm/fixmap.h

@@ -26,29 +26,18 @@
 #include <linux/bug.h>
 #include <asm/page.h>
 
-/*
- * On OpenRISC we use these special fixed_addresses for doing ioremap
- * early in the boot process before memory initialization is complete.
- * This is used, in particular, by the early serial console code.
- *
- * It's not really 'fixmap', per se, but fits loosely into the same
- * paradigm.
- */
 enum fixed_addresses {
-	/*
-	 * FIX_IOREMAP entries are useful for mapping physical address
-	 * space before ioremap() is useable, e.g. really early in boot
-	 * before kmalloc() is working.
-	 */
-#define FIX_N_IOREMAPS  32
-	FIX_IOREMAP_BEGIN,
-	FIX_IOREMAP_END = FIX_IOREMAP_BEGIN + FIX_N_IOREMAPS - 1,
+	FIX_EARLYCON_MEM_BASE,
 	__end_of_fixed_addresses
 };
 
 #define FIXADDR_SIZE		(__end_of_fixed_addresses << PAGE_SHIFT)
 /* FIXADDR_BOTTOM might be a better name here... */
 #define FIXADDR_START		(FIXADDR_TOP - FIXADDR_SIZE)
+#define FIXMAP_PAGE_IO		PAGE_KERNEL_NOCACHE
+
+extern void __set_fixmap(enum fixed_addresses idx,
+			 phys_addr_t phys, pgprot_t flags);
 
 #include <asm-generic/fixmap.h>
 

arch/openrisc/mm/init.c

@@ -207,6 +207,43 @@ void __init mem_init(void)
 	return;
 }
 
+static int __init map_page(unsigned long va, phys_addr_t pa, pgprot_t prot)
+{
+	p4d_t *p4d;
+	pud_t *pud;
+	pmd_t *pmd;
+	pte_t *pte;
+
+	p4d = p4d_offset(pgd_offset_k(va), va);
+	pud = pud_offset(p4d, va);
+	pmd = pmd_offset(pud, va);
+	pte = pte_alloc_kernel(pmd, va);
+
+	if (pte == NULL)
+		return -ENOMEM;
+
+	if (pgprot_val(prot))
+		set_pte_at(&init_mm, va, pte, pfn_pte(pa >> PAGE_SHIFT, prot));
+	else
+		pte_clear(&init_mm, va, pte);
+
+	local_flush_tlb_page(NULL, va);
+	return 0;
+}
+
+void __init __set_fixmap(enum fixed_addresses idx,
+			 phys_addr_t phys, pgprot_t prot)
+{
+	unsigned long address = __fix_to_virt(idx);
+
+	if (idx >= __end_of_fixed_addresses) {
+		BUG();
+		return;
+	}
+
+	map_page(address, phys, prot);
+}
+
 static const pgprot_t protection_map[16] = {
 	[VM_NONE]					= PAGE_NONE,
 	[VM_READ]					= PAGE_READONLY_X,