ARCv2: PAE40: set MSB even if !CONFIG_ARC_HAS_PAE40 but PAE exists in…

… SoC

PAE40 confiuration in hardware extends some of the address registers
for TLB/cache ops to 2 words.

So far kernel was NOT setting the higher word if feature was not enabled
in software which is wrong. Those need to be set to 0 in such case.

Normally this would be done in the cache flush / tlb ops, however since
these registers only exist conditionally, this would have to be
conditional to a flag being set on boot which is expensive/ugly -
specially for the more common case of PAE exists but not in use.
Optimize that by zero'ing them once at boot - nobody will write to
them afterwards

Cc: stable@vger.kernel.org   #4.4+
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/mmu.h

@@ -94,6 +94,8 @@ static inline int is_pae40_enabled(void)
 	return IS_ENABLED(CONFIG_ARC_HAS_PAE40);
 }
 
+extern int pae40_exist_but_not_enab(void);
+
 #endif	/* !__ASSEMBLY__ */
 
 #endif

arch/arc/mm/cache.c

@@ -1123,6 +1123,13 @@ noinline void __init arc_ioc_setup(void)
 	__dc_enable();
 }
 
+/*
+ * Cache related boot time checks/setups only needed on master CPU:
+ *  - Geometry checks (kernel build and hardware agree: e.g. L1_CACHE_BYTES)
+ *    Assume SMP only, so all cores will have same cache config. A check on
+ *    one core suffices for all
+ *  - IOC setup / dma callbacks only need to be done once
+ */
 void __init arc_cache_init_master(void)
 {
 	unsigned int __maybe_unused cpu = smp_processor_id();
@@ -1202,12 +1209,27 @@ void __ref arc_cache_init(void)
 
 	printk(arc_cache_mumbojumbo(0, str, sizeof(str)));
 
-	/*
-	 * Only master CPU needs to execute rest of function:
-	 *  - Assume SMP so all cores will have same cache config so
-	 *    any geomtry checks will be same for all
-	 *  - IOC setup / dma callbacks only need to be setup once
-	 */
 	if (!cpu)
 		arc_cache_init_master();
+
+	/*
+	 * In PAE regime, TLB and cache maintenance ops take wider addresses
+	 * And even if PAE is not enabled in kernel, the upper 32-bits still need
+	 * to be zeroed to keep the ops sane.
+	 * As an optimization for more common !PAE enabled case, zero them out
+	 * once at init, rather than checking/setting to 0 for every runtime op
+	 */
+	if (is_isa_arcv2() && pae40_exist_but_not_enab()) {
+
+		if (IS_ENABLED(CONFIG_ARC_HAS_ICACHE))
+			write_aux_reg(ARC_REG_IC_PTAG_HI, 0);
+
+		if (IS_ENABLED(CONFIG_ARC_HAS_DCACHE))
+			write_aux_reg(ARC_REG_DC_PTAG_HI, 0);
+
+		if (l2_line_sz) {
+			write_aux_reg(ARC_REG_SLC_RGN_END1, 0);
+			write_aux_reg(ARC_REG_SLC_RGN_START1, 0);
+		}
+	}
 }

arch/arc/mm/tlb.c

@@ -104,6 +104,8 @@
 /* A copy of the ASID from the PID reg is kept in asid_cache */
 DEFINE_PER_CPU(unsigned int, asid_cache) = MM_CTXT_FIRST_CYCLE;
 
+static int __read_mostly pae_exists;
+
 /*
  * Utility Routine to erase a J-TLB entry
  * Caller needs to setup Index Reg (manually or via getIndex)
@@ -784,7 +786,7 @@ void read_decode_mmu_bcr(void)
 		mmu->u_dtlb = mmu4->u_dtlb * 4;
 		mmu->u_itlb = mmu4->u_itlb * 4;
 		mmu->sasid = mmu4->sasid;
-		mmu->pae = mmu4->pae;
+		pae_exists = mmu->pae = mmu4->pae;
 	}
 }
 
@@ -809,6 +811,11 @@ char *arc_mmu_mumbojumbo(int cpu_id, char *buf, int len)
 	return buf;
 }
 
+int pae40_exist_but_not_enab(void)
+{
+	return pae_exists && !is_pae40_enabled();
+}
+
 void arc_mmu_init(void)
 {
 	char str[256];
@@ -859,6 +866,9 @@ void arc_mmu_init(void)
 	/* swapper_pg_dir is the pgd for the kernel, used by vmalloc */
 	write_aux_reg(ARC_REG_SCRATCH_DATA0, swapper_pg_dir);
 #endif
+
+	if (pae40_exist_but_not_enab())
+		write_aux_reg(ARC_REG_TLBPD1HI, 0);
 }
 
 /*