[PATCH 7/7] arm64: Add simple earlyprintk support

Catalin Marinas
2012-12-07T21:06:32Z

This patch adds support for "earlyprintk=" parameter on the kernel
command line. The format is:

earlyprintk=<name>[,<addr>][,<options>]

where <name> is the name of the (UART) device, e.g. "pl011", <addr> is
the I/O address. The <options> aren't currently used.

The mapping of the earlyprintk device is done very early during kernel
boot and there are restrictions on which functions it can call. A
special early_io_map() function is added which creates the mapping from
the pre-defined EARLY_IOBASE to the device I/O address passed via the
kernel parameter. The pgd entry corresponding to EARLY_IOBASE is
pre-populated in head.S during kernel boot.

Only PL011 is currently supported and it is assumed that the interface
is already initialised by the boot loader before the kernel is started.

Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
---
Documentation/arm64/memory.txt | 2 +
arch/arm64/Kconfig.debug | 9 +++
arch/arm64/include/asm/io.h | 3 +
arch/arm64/include/asm/memory.h | 1 +
arch/arm64/include/asm/mmu.h | 1 +
arch/arm64/kernel/Makefile | 1 +
arch/arm64/kernel/early_printk.c | 118 +++++++++++++++++++++++++++++++++++++++
arch/arm64/kernel/head.S | 12 +++-
arch/arm64/mm/mmu.c | 42 ++++++++++++++
9 files changed, 187 insertions(+), 2 deletions(-)
create mode 100644 arch/arm64/kernel/early_printk.c

diff --git a/Documentation/arm64/memory.txt b/Documentation/arm64/memory.txt
index d758702..5f583af 100644
--- a/Documentation/arm64/memory.txt
+++ b/Documentation/arm64/memory.txt
@@ -35,6 +35,8 @@ ffffffbc00000000 ffffffbdffffffff 8GB vmemmap

ffffffbe00000000 ffffffbffbbfffff ~8GB [guard, future vmmemap]

+ffffffbffbc00000 ffffffbffbdfffff 2MB earlyprintk device
+
ffffffbffbe00000 ffffffbffbe0ffff 64KB PCI I/O space

ffffffbbffff0000 ffffffbcffffffff ~2MB [guard]
diff --git a/arch/arm64/Kconfig.debug b/arch/arm64/Kconfig.debug
index d7553f2..79871cd 100644
--- a/arch/arm64/Kconfig.debug
+++ b/arch/arm64/Kconfig.debug
@@ -24,4 +24,13 @@ config DEBUG_STACK_USAGE
Enables the display of the minimum amount of free stack which each
task has ever had available in the sysrq-T output.

+config EARLY_PRINTK
+ bool "Early printk support"
+ default y
+ help
+ Say Y here if you want to have an early console using the
+ earlyprintk=<name>[,<addr>][,<options>] kernel parameter. It
+ is assumed that the early console device has been initialised
+ by the boot loader prior to starting the Linux kernel.
+
endmenu
diff --git a/arch/arm64/include/asm/io.h b/arch/arm64/include/asm/io.h
index d2f05a6..57f12c9 100644
--- a/arch/arm64/include/asm/io.h
+++ b/arch/arm64/include/asm/io.h
@@ -230,6 +230,9 @@ extern void __iounmap(volatile void __iomem *addr);
#define ioremap_wc(addr, size) __ioremap((addr), (size), __pgprot(PROT_NORMAL_NC))
#define iounmap __iounmap

+#define PROT_SECT_DEFAULT (PMD_TYPE_SECT | PMD_SECT_AF)
+#define PROT_SECT_DEVICE_nGnRE (PROT_SECT_DEFAULT | PTE_PXN | PTE_UXN | PMD_ATTRINDX(MT_DEVICE_nGnRE))
+
#define ARCH_HAS_IOREMAP_WC
#include <asm-generic/iomap.h>

diff --git a/arch/arm64/include/asm/memory.h b/arch/arm64/include/asm/memory.h
index 1cac16a..381f556 100644
--- a/arch/arm64/include/asm/memory.h
+++ b/arch/arm64/include/asm/memory.h
@@ -43,6 +43,7 @@
#define PAGE_OFFSET UL(0xffffffc000000000)
#define MODULES_END (PAGE_OFFSET)
#define MODULES_VADDR (MODULES_END - SZ_64M)
+#define EARLYCON_IOBASE (MODULES_VADDR - SZ_4M)
#define VA_BITS (39)
#define TASK_SIZE_64 (UL(1) << VA_BITS)

diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h
index d4f7fd5..2494fc0 100644
--- a/arch/arm64/include/asm/mmu.h
+++ b/arch/arm64/include/asm/mmu.h
@@ -26,5 +26,6 @@ typedef struct {

extern void paging_init(void);
extern void setup_mm_for_reboot(void);
+extern void __iomem *early_io_map(phys_addr_t phys, unsigned long virt);

#endif
diff --git a/arch/arm64/kernel/Makefile b/arch/arm64/kernel/Makefile
index e2caff1..623c098 100644
--- a/arch/arm64/kernel/Makefile
+++ b/arch/arm64/kernel/Makefile
@@ -16,6 +16,7 @@ arm64-obj-$(CONFIG_MODULES) += arm64ksyms.o module.o
arm64-obj-$(CONFIG_SMP) += smp.o
arm64-obj-$(CONFIG_HW_PERF_EVENTS) += perf_event.o
arm64-obj-$(CONFIG_HAVE_HW_BREAKPOINT)+= hw_breakpoint.o
+arm64-obj-$(CONFIG_EARLY_PRINTK) += early_printk.o

obj-y += $(arm64-obj-y) vdso/
obj-m += $(arm64-obj-m)
diff --git a/arch/arm64/kernel/early_printk.c b/arch/arm64/kernel/early_printk.c
new file mode 100644
index 0000000..7e320a2
--- /dev/null
+++ b/arch/arm64/kernel/early_printk.c
@@ -0,0 +1,118 @@
+/*
+ * Earlyprintk support.
+ *
+ * Copyright (C) 2012 ARM Ltd.
+ * Author: Catalin Marinas <catalin.marinas@arm.com>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+#include <linux/kernel.h>
+#include <linux/console.h>
+#include <linux/init.h>
+#include <linux/string.h>
+#include <linux/mm.h>
+#include <linux/io.h>
+
+#include <linux/amba/serial.h>
+
+static void __iomem *early_base;
+static void (*printch)(char ch);
+
+/*
+ * PL011 single character TX.
+ */
+static void pl011_printch(char ch)
+{
+ while (readl_relaxed(early_base + UART01x_FR) & UART01x_FR_TXFF)
+ ;
+ writeb_relaxed(ch, early_base + UART01x_DR);
+ while (readl_relaxed(early_base + UART01x_FR) & UART01x_FR_BUSY)
+ ;
+}
+
+struct earlycon_match {
+ const char *name;
+ void (*printch)(char ch);
+};
+
+static const struct earlycon_match earlycon_match[] __initconst = {
+ { .name = "pl011", .printch = pl011_printch, },
+ {}
+};
+
+static void early_write(struct console *con, const char *s, unsigned n)
+{
+ while (n-- > 0) {
+ if (*s == '\n')
+ printch('\r');
+ printch(*s);
+ s++;
+ }
+}
+
+static struct console early_console = {
+ .name = "earlycon",
+ .write = early_write,
+ .flags = CON_PRINTBUFFER | CON_BOOT,
+ .index = -1,
+};
+
+/*
+ * Parse earlyprintk=... parameter in the format:
+ *
+ * <name>[,<addr>][,<options>]
+ *
+ * and register the early console. It is assumed that the UART has been
+ * initialised by the bootloader already.
+ */
+static int __init setup_early_printk(char *buf)
+{
+ const struct earlycon_match *match = earlycon_match;
+ phys_addr_t paddr = 0;
+
+ if (!buf) {
+ pr_warning("No earlyprintk arguments passed.\n");
+ return 0;
+ }
+
+ while (match->name) {
+ size_t len = strlen(match->name);
+ if (!strncmp(buf, match->name, len)) {
+ buf += len;
+ break;
+ }
+ match++;
+ }
+ if (!match->name) {
+ pr_warning("Unknown earlyprintk arguments: %s\n", buf);
+ return 0;
+ }
+
+ /* I/O address */
+ if (!strncmp(buf, ",0x", 3)) {
+ char *e;
+ paddr = simple_strtoul(buf + 1, &e, 16);
+ buf = e;
+ }
+ /* no options parsing yet */
+
+ if (paddr)
+ early_base = early_io_map(paddr, EARLYCON_IOBASE);
+
+ printch = match->printch;
+ register_console(&early_console);
+
+ return 0;
+}
+
+early_param("earlyprintk", setup_early_printk);
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index a2f02b6..4fcc379 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -81,10 +81,8 @@

#ifdef CONFIG_ARM64_64K_PAGES
#define MM_MMUFLAGS PTE_ATTRINDX(MT_NORMAL) | PTE_FLAGS
-#define IO_MMUFLAGS PTE_ATTRINDX(MT_DEVICE_nGnRE) | PTE_XN | PTE_FLAGS
#else
#define MM_MMUFLAGS PMD_ATTRINDX(MT_NORMAL) | PMD_FLAGS
-#define IO_MMUFLAGS PMD_ATTRINDX(MT_DEVICE_nGnRE) | PMD_SECT_XN | PMD_FLAGS
#endif

/*
@@ -341,6 +339,7 @@ ENDPROC(__calc_phys_offset)
* - identity mapping to enable the MMU (low address, TTBR0)
* - first few MB of the kernel linear mapping to jump to once the MMU has
* been enabled, including the FDT blob (TTBR1)
+ * - UART mapping if CONFIG_EARLY_PRINTK is enabled (TTBR1)
*/
__create_page_tables:
pgtbl x25, x26, x24 // idmap_pg_dir and swapper_pg_dir addresses
@@ -393,6 +392,15 @@ __create_page_tables:
sub x6, x6, #1 // inclusive range
create_block_map x0, x7, x3, x5, x6
1:
+#ifdef CONFIG_EARLY_PRINTK
+ /*
+ * Create the pgd entry for the UART mapping. The full mapping is done
+ * later based earlyprintk kernel parameter.
+ */
+ ldr x5, =EARLYCON_IOBASE // UART virtual address
+ add x0, x26, #2 * PAGE_SIZE // section table address
+ create_pgd_entry x26, x0, x5, x6, x7
+#endif
ret
ENDPROC(__create_page_tables)
.ltorg
diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
index a6885d8..f4dd585 100644
--- a/arch/arm64/mm/mmu.c
+++ b/arch/arm64/mm/mmu.c
@@ -25,6 +25,7 @@
#include <linux/nodemask.h>
#include <linux/memblock.h>
#include <linux/fs.h>
+#include <linux/io.h>

#include <asm/cputype.h>
#include <asm/sections.h>
@@ -251,6 +252,47 @@ static void __init create_mapping(phys_addr_t phys, unsigned long virt,
} while (pgd++, addr = next, addr != end);
}

+#ifdef CONFIG_EARLY_PRINTK
+/*
+ * Create an early I/O mapping using the pgd/pmd entries already populated
+ * in head.S as this function is called too early to allocated any memory. The
+ * mapping size is 2MB with 4KB pages or 64KB or 64KB pages.
+ */
+void __iomem * __init early_io_map(phys_addr_t phys, unsigned long virt)
+{
+ unsigned long size, mask;
+ bool page64k = IS_ENABLED(ARM64_64K_PAGES);
+ pgd_t *pgd;
+ pud_t *pud;
+ pmd_t *pmd;
+ pte_t *pte;
+
+ /*
+ * No early pte entries with !ARM64_64K_PAGES configuration, so using
+ * sections (pmd).
+ */
+ size = page64k ? PAGE_SIZE : SECTION_SIZE;
+ mask = ~(size - 1);
+
+ pgd = pgd_offset_k(virt);
+ pud = pud_offset(pgd, virt);
+ if (pud_none(*pud))
+ return NULL;
+ pmd = pmd_offset(pud, virt);
+
+ if (page64k) {
+ if (pmd_none(*pmd))
+ return NULL;
+ pte = pte_offset_kernel(pmd, virt);
+ set_pte(pte, __pte((phys & mask) | PROT_DEVICE_nGnRE));
+ } else {
+ set_pmd(pmd, __pmd((phys & mask) | PROT_SECT_DEVICE_nGnRE));
+ }
+
+ return (void __iomem *)((virt & mask) + (phys & ~mask));
+}
+#endif
+
static void __init map_mem(void)
{
struct memblock_region *reg;