[PATCH 11/14] arm64: big-endian: set correct endianess on kernel entry
From: Christopher Covington <hidden>
Date: 2013-10-15 18:46:41
Hi Matthew, On 10/11/2013 09:52 AM, Matthew Leach wrote:
The endianness of memory accesses at EL2 and EL1 are configured by
SCTLR_EL2.EE and SCTLR_EL1.EE respectively. When the kernel is booted,
the state of SCTLR_EL{2,1}.EE is unknown, and thus the kernel must
ensure that they are set before performing any memory accesses.
This patch ensures that SCTLR_EL{2,1} are configured appropriately at
boot for kernels of either endianness.[...]
quoted hunk ↗ jump to hunk
--- a/arch/arm64/kernel/head.S +++ b/arch/arm64/kernel/head.S@@ -159,12 +159,22 @@ ENTRY(el2_setup) mrs x0, CurrentEL cmp x0, #PSR_MODE_EL2t ccmp x0, #PSR_MODE_EL2h, #0x4, ne - b.eq 1f + b.ne 1f + mrs x0, sctlr_el2 +CPU_BE( orr x0, x0, #(1 << 25) ) // Set the EE bit for EL2 +CPU_LE( bic x0, x0, #(1 << 25) ) // Clear the EE bit for EL2 + msr sctlr_el2, x0 + b 2f +1: mrs x0, sctlr_el1 +CPU_BE( orr x0, x0, #(2 << 24) ) // Set the EE and E0E bits for EL1 +CPU_LE( bic x0, x0, #(2 << 24) ) // Clear the EE and E0E bits for EL1 + msr sctlr_el1, x0 mov w20, #BOOT_CPU_MODE_EL1 // This cpu booted in EL1 + isb
Could you please comment on why this barrier is necessary?
quoted hunk ↗ jump to hunk
ret /* Hyp configuration. */ -1: mov x0, #(1 << 31) // 64-bit EL1 +2: mov x0, #(1 << 31) // 64-bit EL1 msr hcr_el2, x0 /* Generic timers. */@@ -181,7 +191,8 @@ ENTRY(el2_setup) /* sctlr_el1 */ mov x0, #0x0800 // Set/clear RES{1,0} bits - movk x0, #0x30d0, lsl #16 +CPU_BE( movk x0, #0x33d0, lsl #16 ) // Set EE and E0E on BE systems +CPU_LE( movk x0, #0x30d0, lsl #16 ) // Clear EE and E0E on LE systems
Although the CPU_[BL]E macros make the ifdef'ery here and above prettier than they would be otherwise, I wonder if making the set and clear operations and this magic number macros instead could improve readability and fall more in line with the "#ifdefs are ugly" guideline in Documentation/SubmittingPatches.
msr sctlr_el1, x0 /* Coprocessor traps. */
[...] Thanks, Christopher -- Employee of Qualcomm Innovation Center, Inc. Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by the Linux Foundation.