DSU: Implement workaround for errata 798953

Under certain near idle conditions, DSU may miss response transfers on
the ACE master or Peripheral port, leading to deadlock. This workaround
disables high-level clock gating of the DSU to prevent this.

Change-Id: I820911d61570bacb38dd325b3519bc8d12caa14b
Signed-off-by: Louis Mayencourt <louis.mayencourt@arm.com>

docs/cpu-specific-build-macros.rst

@@ -233,6 +233,11 @@ of DSU errata workarounds are similar to `CPU errata workarounds`_.
 
 For DSU errata, the following build flags are defined:
 
+-  ``ERRATA_DSU_798953``: This applies errata 798953 workaround for the
+   affected DSU configurations. This errata applies only for those DSUs that
+   revision is r0p0 (on r0p1 it is fixed). However, please note that this
+   workaround results in increased DSU power consumption on idle.
+
 -  ``ERRATA_DSU_936184``: This applies errata 936184 workaround for the
    affected DSU configurations. This errata applies only for those DSUs that
    contain the ACP interface **and** the DSU revision is older than r2p0 (on

include/lib/cpus/aarch64/dsu_def.h

@@ -31,6 +31,8 @@
  ********************************************************************/
 #define CLUSTERACTLR_EL1	S3_0_C15_C3_3
 
+#define CLUSTERACTLR_EL1_DISABLE_CLOCK_GATING	(ULL(1) << 15)
+
 /********************************************************************
  * Masks applied for DSU errata workarounds
  ********************************************************************/

lib/cpus/aarch64/cortex_a55.S

@@ -173,6 +173,10 @@ endfunc check_errata_903758
 func cortex_a55_reset_func
 	mov	x19, x30
 
+#if ERRATA_DSU_798953
+	bl	errata_dsu_798953_wa
+#endif
+
 #if ERRATA_DSU_936184
 	bl	errata_dsu_936184_wa
 #endif
@@ -237,6 +241,7 @@ func cortex_a55_errata_report
 	 * Report all errata. The revision variant information is at x8, where
 	 * "report_errata" is expecting it and it doesn't corrupt it.
 	 */
+	report_errata ERRATA_DSU_798953, cortex_a55, dsu_798953
 	report_errata ERRATA_DSU_936184, cortex_a55, dsu_936184
 	report_errata ERRATA_A55_768277, cortex_a55, 768277
 	report_errata ERRATA_A55_778703, cortex_a55, 778703

lib/cpus/aarch64/cortex_a75.S

@@ -100,6 +100,10 @@ func cortex_a75_reset_func
 	isb
 #endif
 
+#if ERRATA_DSU_798953
+	bl	errata_dsu_798953_wa
+#endif
+
 #if ERRATA_DSU_936184
 	bl	errata_dsu_936184_wa
 #endif
@@ -186,6 +190,7 @@ func cortex_a75_errata_report
 	report_errata ERRATA_A75_790748, cortex_a75, 790748
 	report_errata WORKAROUND_CVE_2017_5715, cortex_a75, cve_2017_5715
 	report_errata WORKAROUND_CVE_2018_3639, cortex_a75, cve_2018_3639
+	report_errata ERRATA_DSU_798953, cortex_a75, dsu_798953
 	report_errata ERRATA_DSU_936184, cortex_a75, dsu_936184
 
 	ldp	x8, x30, [sp], #16

lib/cpus/aarch64/cortex_a76.S

@@ -344,9 +344,14 @@ func cortex_a76_reset_func
 #endif /* DYNAMIC_WORKAROUND_CVE_2018_3639 */
 #endif /* WORKAROUND_CVE_2018_3639 */
 
+#if ERRATA_DSU_798953
+	bl	errata_dsu_798953_wa
+#endif
+
 #if ERRATA_DSU_936184
 	bl	errata_dsu_936184_wa
 #endif
+
 	ret	x19
 endfunc cortex_a76_reset_func
 
@@ -368,7 +373,7 @@ endfunc cortex_a76_core_pwr_dwn
 
 #if REPORT_ERRATA
 /*
- * Errata printing function for Cortex Cortex A76. Must follow AAPCS.
+ * Errata printing function for Cortex A76. Must follow AAPCS.
  */
 func cortex_a76_errata_report
 	stp	x8, x30, [sp, #-16]!
@@ -384,6 +389,7 @@ func cortex_a76_errata_report
 	report_errata ERRATA_A76_1130799, cortex_a76, 1130799
 	report_errata ERRATA_A76_1220197, cortex_a76, 1220197
 	report_errata WORKAROUND_CVE_2018_3639, cortex_a76, cve_2018_3639
+	report_errata ERRATA_DSU_798953, cortex_a76, dsu_798953
 	report_errata ERRATA_DSU_936184, cortex_a76, dsu_936184
 
 	ldp	x8, x30, [sp], #16

lib/cpus/aarch64/dsu_helpers.S

@@ -8,6 +8,59 @@
 #include <dsu_def.h>
 #include <lib/cpus/errata_report.h>
 
+	/* -----------------------------------------------------------------------
+	 * DSU erratum 798953 check function
+	 * Checks the DSU variant, revision and configuration to determine if
+	 * the erratum applies. Erratum applies on all configurations of the
+	 * DSU and if revision-variant is r0p0.
+	 *
+	 * The erratum was fixed in r0p1.
+	 *
+	 * This function is called from both assembly and C environment. So it
+	 * follows AAPCS.
+	 *
+	 * Clobbers: x0-x3
+	 * -----------------------------------------------------------------------
+	 */
+	.globl	check_errata_dsu_798953
+	.globl	errata_dsu_798953_wa
+
+func check_errata_dsu_798953
+	mov	x2, #ERRATA_APPLIES
+	mov	x3, #ERRATA_NOT_APPLIES
+
+	/* Check if DSU is equal to r0p0 */
+	mrs	x1, CLUSTERIDR_EL1
+
+	/* DSU variant and revision bitfields in CLUSTERIDR are adjacent */
+	ubfx	x0, x1, #CLUSTERIDR_REV_SHIFT,\
+			#(CLUSTERIDR_REV_BITS + CLUSTERIDR_VAR_BITS)
+	mov	x1, #(0x0 << CLUSTERIDR_REV_SHIFT)
+	cmp	x0, x1
+	csel	x0, x2, x3, EQ
+	ret
+endfunc check_errata_dsu_798953
+
+	/* --------------------------------------------------
+	 * Errata Workaround for DSU erratum #798953.
+	 *
+	 * Can clobber only: x0-x17
+	 * --------------------------------------------------
+	 */
+func errata_dsu_798953_wa
+	mov	x17, x30
+	bl	check_errata_dsu_798953
+	cbz	x0, 1f
+
+	/* If erratum applies, disable high-level clock gating */
+	mrs	x0, CLUSTERACTLR_EL1
+	orr	x0, x0, #CLUSTERACTLR_EL1_DISABLE_CLOCK_GATING
+	msr	CLUSTERACTLR_EL1, x0
+	isb
+1:
+	ret	x17
+endfunc errata_dsu_798953_wa
+
 	/* -----------------------------------------------------------------------
 	 * DSU erratum 936184 check function
 	 * Checks the DSU variant, revision and configuration to determine if

lib/cpus/cpu-ops.mk

@@ -214,6 +214,10 @@ ERRATA_A76_1220197	?=0
 # only to r0p0 and r1p0 of the Neoverse N1 cpu.
 ERRATA_N1_1043202	?=1
 
+# Flag to apply DSU erratum 798953. This erratum applies to DSUs revision r0p0.
+# Applying the workaround results in higher DSU power consumption on idle.
+ERRATA_DSU_798953	?=0
+
 # Flag to apply DSU erratum 936184. This erratum applies to DSUs containing
 # the ACP interface and revision < r2p0. Applying the workaround results in
 # higher DSU power consumption on idle.
@@ -375,6 +379,10 @@ $(eval $(call add_define,ERRATA_A76_1220197))
 $(eval $(call assert_boolean,ERRATA_N1_1043202))
 $(eval $(call add_define,ERRATA_N1_1043202))
 
+# Process ERRATA_DSU_798953 flag
+$(eval $(call assert_boolean,ERRATA_DSU_798953))
+$(eval $(call add_define,ERRATA_DSU_798953))
+
 # Process ERRATA_DSU_936184 flag
 $(eval $(call assert_boolean,ERRATA_DSU_936184))
 $(eval $(call add_define,ERRATA_DSU_936184))