Cortex-A55: Implement workaround for erratum 903758

Change-Id: I07e69061ba7a918cdfaaa83fa3a42dee910887d7
Signed-off-by: Ambroise Vincent <ambroise.vincent@arm.com>

docs/cpu-specific-build-macros.rst

@@ -111,6 +111,9 @@ For Cortex-A55, the following errata build flags are defined :
 -  ``ERRATA_A55_846532``: This applies errata 846532 workaround to Cortex-A55
    CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
 
+-  ``ERRATA_A55_903758``: This applies errata 903758 workaround to Cortex-A55
+   CPU. This needs to be enabled only for revision <= r0p1 of the CPU.
+
 For Cortex-A57, the following errata build flags are defined :
 
 -  ``ERRATA_A57_806969``: This applies errata 806969 workaround to Cortex-A57

lib/cpus/aarch64/cortex_a55.S

@@ -142,6 +142,34 @@ func check_errata_846532
 	b	cpu_rev_var_ls
 endfunc check_errata_846532
 
+	/* -----------------------------------------------------
+	 * Errata Workaround for Cortex A55 Errata #903758.
+	 * This applies only to revisions <= r0p1 of Cortex A55.
+	 * Inputs:
+	 * x0: variant[4:7] and revision[0:3] of current cpu.
+	 * Shall clobber: x0-x17
+	 * -----------------------------------------------------
+	 */
+func errata_a55_903758_wa
+	/*
+	 * Compare x0 against revision r0p1
+	 */
+	mov	x17, x30
+	bl	check_errata_903758
+	cbz	x0, 1f
+	mrs	x1, CORTEX_A55_CPUACTLR_EL1
+	orr	x1, x1, #CORTEX_A55_CPUACTLR_EL1_DISABLE_L1_PAGEWALKS
+	msr	CORTEX_A55_CPUACTLR_EL1, x1
+	isb
+1:
+	ret	x17
+endfunc errata_a55_903758_wa
+
+func check_errata_903758
+	mov	x1, #0x01
+	b	cpu_rev_var_ls
+endfunc check_errata_903758
+
 func cortex_a55_reset_func
 	mov	x19, x30
 
@@ -172,6 +200,11 @@ func cortex_a55_reset_func
 	bl	errata_a55_846532_wa
 #endif
 
+#if ERRATA_A55_903758
+	mov	x0, x18
+	bl	errata_a55_903758_wa
+#endif
+
 	ret	x19
 endfunc cortex_a55_reset_func
 
@@ -209,6 +242,7 @@ func cortex_a55_errata_report
 	report_errata ERRATA_A55_778703, cortex_a55, 778703
 	report_errata ERRATA_A55_798797, cortex_a55, 798797
 	report_errata ERRATA_A55_846532, cortex_a55, 846532
+	report_errata ERRATA_A55_903758, cortex_a55, 903758
 
 	ldp	x8, x30, [sp], #16
 	ret

lib/cpus/cpu-ops.mk

@@ -95,6 +95,10 @@ ERRATA_A55_798797	?=0
 # only to revision <= r0p1 of the Cortex A55 cpu.
 ERRATA_A55_846532	?=0
 
+# Flag to apply erratum 903758 workaround during reset. This erratum applies
+# only to revision <= r0p1 of the Cortex A55 cpu.
+ERRATA_A55_903758	?=0
+
 # Flag to apply erratum 806969 workaround during reset. This erratum applies
 # only to revision r0p0 of the Cortex A57 cpu.
 ERRATA_A57_806969	?=0
@@ -180,6 +184,10 @@ $(eval $(call add_define,ERRATA_A55_798797))
 $(eval $(call assert_boolean,ERRATA_A55_846532))
 $(eval $(call add_define,ERRATA_A55_846532))
 
+# Process ERRATA_A55_903758 flag
+$(eval $(call assert_boolean,ERRATA_A55_903758))
+$(eval $(call add_define,ERRATA_A55_903758))
+
 # Process ERRATA_A57_806969 flag
 $(eval $(call assert_boolean,ERRATA_A57_806969))
 $(eval $(call add_define,ERRATA_A57_806969))