riscv: drop some idefs from CMO initialization

Wrapping things in #ifdefs makes the code harder to read
while we also have IS_ENABLED() macros to do this in regular code
and the extension detection is not _that_ runtime critical.

So define a stub for riscv_noncoherent_supported() in the
non-CONFIG_RISCV_DMA_NONCOHERENT case and move the code to
us IS_ENABLED.
Suggested-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Guo Ren <guoren@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20220905111027.2463297-3-heiko@sntech.deSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/errata/thead/errata.c

@@ -30,7 +30,9 @@ static bool errata_probe_pbmt(unsigned int stage,
 static bool errata_probe_cmo(unsigned int stage,
 			     unsigned long arch_id, unsigned long impid)
 {
-#ifdef CONFIG_ERRATA_THEAD_CMO
+	if (!IS_ENABLED(CONFIG_ERRATA_THEAD_CMO))
+		return false;
+
 	if (arch_id != 0 || impid != 0)
 		return false;
 
@@ -39,9 +41,6 @@ static bool errata_probe_cmo(unsigned int stage,
 
 	riscv_noncoherent_supported();
 	return true;
-#else
-	return false;
-#endif
 }
 
 static u32 thead_errata_probe(unsigned int stage,

arch/riscv/include/asm/cacheflush.h

@@ -50,6 +50,8 @@ static inline void riscv_init_cbom_blocksize(void) { }
 
 #ifdef CONFIG_RISCV_DMA_NONCOHERENT
 void riscv_noncoherent_supported(void);
+#else
+static inline void riscv_noncoherent_supported(void) {}
 #endif
 
 /*

arch/riscv/kernel/cpufeature.c

@@ -264,21 +264,17 @@ static bool __init_or_module cpufeature_probe_svpbmt(unsigned int stage)
 
 static bool __init_or_module cpufeature_probe_zicbom(unsigned int stage)
 {
-#ifdef CONFIG_RISCV_ISA_ZICBOM
-	switch (stage) {
-	case RISCV_ALTERNATIVES_EARLY_BOOT:
+	if (!IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM))
+		return false;
+
+	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
+		return false;
+
+	if (!riscv_isa_extension_available(NULL, ZICBOM))
 		return false;
-	default:
-		if (riscv_isa_extension_available(NULL, ZICBOM)) {
-			riscv_noncoherent_supported();
-			return true;
-		} else {
-			return false;
-		}
-	}
-#endif
 
-	return false;
+	riscv_noncoherent_supported();
+	return true;
 }
 
 /*