[PATCH v3] parisc: Avoid calling SMP cache flush functions on cache-less machines

[Helge Deller <deller@xxxxxx>]

At least the qemu virtual machine does not provide D- and I-caches,
so skip triggering SMP irqs to flush caches on such machines.

Further optimize the caching code by using static branches and making
some functions static.

Signed-off-by: Helge Deller <deller@xxxxxx>

---
v3: re-introduce flush_data_cache()
v2: rewrite with static keys as suggested by Sven Schnelle, and rework all
    cache functions (e.g. make many static)

diff --git a/arch/parisc/include/asm/cacheflush.h b/arch/parisc/include/asm/cacheflush.h
index 859b8a34adcf..e8b4a03343d3 100644
--- a/arch/parisc/include/asm/cacheflush.h
+++ b/arch/parisc/include/asm/cacheflush.h
@@ -9,16 +9,11 @@
 /* The usual comment is "Caches aren't brain-dead on the <architecture>".
  * Unfortunately, that doesn't apply to PA-RISC. */

-/* Internal implementation */
-void flush_data_cache_local(void *);  /* flushes local data-cache only */
-void flush_instruction_cache_local(void *); /* flushes local code-cache only */
-#ifdef CONFIG_SMP
-void flush_data_cache(void); /* flushes data-cache only (all processors) */
-void flush_instruction_cache(void); /* flushes i-cache only (all processors) */
-#else
-#define flush_data_cache() flush_data_cache_local(NULL)
-#define flush_instruction_cache() flush_instruction_cache_local(NULL)
-#endif
+#include <linux/jump_label.h>
+
+DECLARE_STATIC_KEY_TRUE(parisc_has_cache);
+DECLARE_STATIC_KEY_TRUE(parisc_has_dcache);
+DECLARE_STATIC_KEY_TRUE(parisc_has_icache);

 #define flush_cache_dup_mm(mm) flush_cache_mm(mm)

diff --git a/arch/parisc/kernel/alternative.c b/arch/parisc/kernel/alternative.c
index fa28c4c9f972..daa1e9047275 100644
--- a/arch/parisc/kernel/alternative.c
+++ b/arch/parisc/kernel/alternative.c
@@ -8,6 +8,7 @@
 #include <asm/processor.h>
 #include <asm/sections.h>
 #include <asm/alternative.h>
+#include <asm/cacheflush.h>

 #include <linux/module.h>

@@ -107,5 +108,14 @@ void __init apply_alternatives_all(void)
 	apply_alternatives((struct alt_instr *) &__alt_instructions,
 		(struct alt_instr *) &__alt_instructions_end, NULL);

+	if (cache_info.dc_size == 0 && cache_info.ic_size == 0) {
+		pr_info("alternatives: optimizing cache-flushes.\n");
+		static_branch_disable(&parisc_has_cache);
+	}
+	if (cache_info.dc_size == 0)
+		static_branch_disable(&parisc_has_dcache);
+	if (cache_info.ic_size == 0)
+		static_branch_disable(&parisc_has_icache);
+
 	set_kernel_text_rw(0);
 }
diff --git a/arch/parisc/kernel/cache.c b/arch/parisc/kernel/cache.c
index 81f36d6407f0..231cebb3fc0d 100644
--- a/arch/parisc/kernel/cache.c
+++ b/arch/parisc/kernel/cache.c
@@ -38,6 +38,9 @@ EXPORT_SYMBOL(flush_dcache_page_asm);
 void purge_dcache_page_asm(unsigned long phys_addr, unsigned long vaddr);
 void flush_icache_page_asm(unsigned long phys_addr, unsigned long vaddr);

+/* Internal implementation in arch/parisc/kernel/pacache.S */
+void flush_data_cache_local(void *);  /* flushes local data-cache only */
+void flush_instruction_cache_local(void); /* flushes local code-cache only */

 /* On some machines (i.e., ones with the Merced bus), there can be
  * only a single PxTLB broadcast at a time; this must be guaranteed
@@ -58,26 +61,35 @@ struct pdc_cache_info cache_info __ro_after_init;
 static struct pdc_btlb_info btlb_info __ro_after_init;
 #endif

-#ifdef CONFIG_SMP
-void
-flush_data_cache(void)
+DEFINE_STATIC_KEY_TRUE(parisc_has_cache);
+DEFINE_STATIC_KEY_TRUE(parisc_has_dcache);
+DEFINE_STATIC_KEY_TRUE(parisc_has_icache);
+
+static void cache_flush_local_cpu(void *dummy)
 {
-	on_each_cpu(flush_data_cache_local, NULL, 1);
+	if (static_branch_likely(&parisc_has_icache))
+		flush_instruction_cache_local();
+	if (static_branch_likely(&parisc_has_dcache))
+		flush_data_cache_local(NULL);
 }
-void
-flush_instruction_cache(void)
+
+void flush_cache_all_local(void)
 {
-	on_each_cpu(flush_instruction_cache_local, NULL, 1);
+	cache_flush_local_cpu(NULL);
 }
-#endif

-void
-flush_cache_all_local(void)
+void flush_cache_all(void)
+{
+	if (static_branch_likely(&parisc_has_cache))
+		on_each_cpu(cache_flush_local_cpu, NULL, 1);
+}
+
+static inline void flush_data_cache(void)
 {
-	flush_instruction_cache_local(NULL);
-	flush_data_cache_local(NULL);
+	if (static_branch_likely(&parisc_has_dcache))
+		on_each_cpu(flush_data_cache_local, NULL, 1);
 }
-EXPORT_SYMBOL(flush_cache_all_local);
+

 /* Virtual address of pfn.  */
 #define pfn_va(pfn)	__va(PFN_PHYS(pfn))
@@ -375,7 +387,6 @@ EXPORT_SYMBOL(flush_dcache_page);

 /* Defined in arch/parisc/kernel/pacache.S */
 EXPORT_SYMBOL(flush_kernel_dcache_range_asm);
-EXPORT_SYMBOL(flush_data_cache_local);
 EXPORT_SYMBOL(flush_kernel_icache_range_asm);

 #define FLUSH_THRESHOLD 0x80000 /* 0.5MB */
@@ -517,16 +528,6 @@ int __flush_tlb_range(unsigned long sid, unsigned long start,
 	return 0;
 }

-static void cacheflush_h_tmp_function(void *dummy)
-{
-	flush_cache_all_local();
-}
-
-void flush_cache_all(void)
-{
-	on_each_cpu(cacheflush_h_tmp_function, NULL, 1);
-}
-
 static inline unsigned long mm_total_size(struct mm_struct *mm)
 {
 	struct vm_area_struct *vma;