[PATCH 2/2] arm64: setup: name `tcr` register

[Mark Rutland]

In __cpu_setup we conditionally manipulate the TCR_EL1 value in x10
after previously using x10 as a scratch register for unrelated temporary
variables.

To make this a bit clearer, let's move the TCR_EL1 value into a named
register `tcr`. To simplify the register allocation, this is placed in
the highest available caller-saved scratch register, tcr.

Following the example of `mair`, we initialise the register with the
default value prior to any feature discovery, and write it to MAIR_EL1
after all feature discovery is complete, which allows us to simplify the
featuere discovery code.

The existing `mte_tcr` register is no longer needed, and is replaced by
the use of x10 as a temporary, matching the rest of the MTE feature
discovery assembly in __cpu_setup. As x20 is no longer used, the
function is now AAPCS compliant, as we've generally aimed for in our
assembly functions.

There should be no functional change as as a result of this patch.

Signed-off-by: Mark Rutland <mark.rutland at arm.com>
Cc: Catalin Marinas <catalin.marinas at arm.com>
Cc: Marc Zyngier <maz at kernel.org>
Cc: Will Deacon <will at kernel.org>
---
 arch/arm64/mm/proc.S | 39 ++++++++++++++++-----------------------
 1 file changed, 16 insertions(+), 23 deletions(-)

diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S
index f560b6fde34c..0a48191534ff 100644
--- a/arch/arm64/mm/proc.S
+++ b/arch/arm64/mm/proc.S
@@ -419,15 +419,17 @@ SYM_FUNC_START(__cpu_setup)
 	reset_amuserenr_el0 x1			// Disable AMU access from EL0
 
 	/*
-	 * Memory region attributes
+	 * Default values for VMSA control registers. These will be adjusted
+	 * below depending on detected CPU features.
 	 */
 	mair	.req	x17
+	tcr	.req	x16
 	mov_q	mair, MAIR_EL1_SET
-#ifdef CONFIG_ARM64_MTE
-	mte_tcr	.req	x20
-
-	mov	mte_tcr, #0
+	mov_q	tcr, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
+			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
+			TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS
 
+#ifdef CONFIG_ARM64_MTE
 	/*
 	 * Update MAIR_EL1, GCR_EL1 and TFSR*_EL1 if MTE is supported
 	 * (ID_AA64PFR1_EL1[11:8] > 1).
@@ -450,36 +452,26 @@ SYM_FUNC_START(__cpu_setup)
 	msr_s	SYS_TFSRE0_EL1, xzr
 
 	/* set the TCR_EL1 bits */
-	mov_q	mte_tcr, TCR_KASAN_HW_FLAGS
+	mov_q	x10, TCR_KASAN_HW_FLAGS
+	orr	tcr, tcr, x10
 1:
 #endif
-	/*
-	 * Set/prepare TCR and TTBR. TCR_EL1.T1SZ gets further
-	 * adjusted if the kernel is compiled with 52bit VA support.
-	 */
-	mov_q	x10, TCR_TxSZ(VA_BITS) | TCR_CACHE_FLAGS | TCR_SMP_FLAGS | \
-			TCR_TG_FLAGS | TCR_KASLR_FLAGS | TCR_ASID16 | \
-			TCR_TBI0 | TCR_A1 | TCR_KASAN_SW_FLAGS
-#ifdef CONFIG_ARM64_MTE
-	orr	x10, x10, mte_tcr
-	.unreq	mte_tcr
-#endif
-	tcr_clear_errata_bits x10, x9, x5
+	tcr_clear_errata_bits tcr, x9, x5
 
 #ifdef CONFIG_ARM64_VA_BITS_52
 	ldr_l		x9, vabits_actual
 	sub		x9, xzr, x9
 	add		x9, x9, #64
-	tcr_set_t1sz	x10, x9
+	tcr_set_t1sz	tcr, x9
 #else
 	ldr_l		x9, idmap_t0sz
 #endif
-	tcr_set_t0sz	x10, x9
+	tcr_set_t0sz	tcr, x9
 
 	/*
 	 * Set the IPS bits in TCR_EL1.
 	 */
-	tcr_compute_pa_size x10, #TCR_IPS_SHIFT, x5, x6
+	tcr_compute_pa_size tcr, #TCR_IPS_SHIFT, x5, x6
 #ifdef CONFIG_ARM64_HW_AFDBM
 	/*
 	 * Enable hardware update of the Access Flags bit.
@@ -489,11 +481,11 @@ SYM_FUNC_START(__cpu_setup)
 	mrs	x9, ID_AA64MMFR1_EL1
 	and	x9, x9, #0xf
 	cbz	x9, 1f
-	orr	x10, x10, #TCR_HA		// hardware Access flag update
+	orr	tcr, tcr, #TCR_HA		// hardware Access flag update
 1:
 #endif	/* CONFIG_ARM64_HW_AFDBM */
 	msr	mair_el1, mair
-	msr	tcr_el1, x10
+	msr	tcr_el1, tcr
 	/*
 	 * Prepare SCTLR
 	 */
@@ -501,4 +493,5 @@ SYM_FUNC_START(__cpu_setup)
 	ret					// return to head.S
 
 	.unreq	mair
+	.unreq	tcr
 SYM_FUNC_END(__cpu_setup)
-- 
2.11.0