Re: [PATCH 12/14] arm64: Check for selected granule support

From: Suzuki K. Poulose
Date: Thu Aug 13 2015 - 10:45:17 EST

On 13/08/15 13:28, Steve Capper wrote:
On 13 August 2015 at 12:34, Suzuki K. Poulose <suzuki.poulose@xxxxxxx> wrote:
From: "Suzuki K. Poulose" <suzuki.poulose@xxxxxxx>

Ensure that the selected page size is supported by the

Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Catalin Marinas <catalin.marinas@xxxxxxx>
Cc: Will Deacon <will.deacon@xxxxxxx>
Signed-off-by: Suzuki K. Poulose <suzuki.poulose@xxxxxxx>
arch/arm64/include/asm/sysreg.h | 6 ++++++
arch/arm64/kernel/head.S | 24 +++++++++++++++++++++++-
2 files changed, 29 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/include/asm/sysreg.h b/arch/arm64/include/asm/sysreg.h
index a7f3d4b..e01d323 100644
--- a/arch/arm64/include/asm/sysreg.h
+++ b/arch/arm64/include/asm/sysreg.h
@@ -87,4 +87,10 @@ static inline void config_sctlr_el1(u32 clear, u32 set)

+#define ID_AA64MMFR0_TGran4_SHIFT 28
+#define ID_AA64MMFR0_TGran64_SHIFT 24
+#define ID_AA64MMFR0_TGran4_ENABLED 0x0
+#define ID_AA64MMFR0_TGran64_ENABLED 0x0
#endif /* __ASM_SYSREG_H */
diff --git a/arch/arm64/kernel/head.S b/arch/arm64/kernel/head.S
index 01b8e58..0cb04db 100644
--- a/arch/arm64/kernel/head.S
+++ b/arch/arm64/kernel/head.S
@@ -31,10 +31,11 @@
#include <asm/cputype.h>
#include <asm/kernel-pgtable.h>
#include <asm/memory.h>
-#include <asm/thread_info.h>
#include <asm/pgtable-hwdef.h>
#include <asm/pgtable.h>
#include <asm/page.h>
+#include <asm/sysreg.h>
+#include <asm/thread_info.h>
#include <asm/virt.h>

@@ -606,9 +607,25 @@ ENDPROC(__secondary_switched)
* x27 = *virtual* address to jump to upon completion
* other registers depend on the function called upon completion
+ * Checks if the selected granule size is supported by the CPU.
+#if defined(CONFIG_ARM64_64K_PAGES)
+#define ID_AA64MMFR0_TGran_SHIFT ID_AA64MMFR0_TGran64_SHIFT
.section ".idmap.text", "ax"
+ mrs x1, ID_AA64MMFR0_EL1
+ ubfx x2, x1, #ID_AA64MMFR0_TGran_SHIFT, 4
+ cmp x2, #ID_AA64MMFR0_TGran_ENABLED
+ __no_granule_support
ldr x5, =vectors
msr vbar_el1, x5
msr ttbr0_el1, x25 // load TTBR0
@@ -626,3 +643,8 @@ __enable_mmu:
br x27
+ wfe
+ b __no_granule_support

Hi Suzuki,
Is is possible to tell the user that the kernel has failed to boot due
to the kernel granule being unsupported?

We don't have anything up at this time. The "looping address" is actually a clue
to the (expert) user. Not sure we can do something, until we get something like DEBUG_LL(?)
Or we should let it continue and end in a panic(?). The current situation can boot a
multi-cluster system with boot cluster having the Tgran support(which doesn't make a
strong use case though). I will try out some options and get back to you.



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