RISC-V: Clean up the Zicbom block size probing

This fixes two issues: I truncated the warning's hart ID when porting to
the 64-bit hart ID code, and the original code's warning handling could
fire on an uninitialized hart ID.

The biggest change here is that riscv_cbom_block_size is no longer
initialized, as IMO the default isn't sane: there's nothing in the ISA
that mandates any specific cache block size, so falling back to one will
just silently produce the wrong answer on some systems.  This also
changes the probing order so the cache block size is known before
enabling Zicbom support.

CC: stable@vger.kernel.org
CC: Andrew Jones <ajones@ventanamicro.com>
CC: Heiko Stuebner <heiko@sntech.de>
CC: Atish Patra <atishp@rivosinc.com>
Fixes: 3aefb2ee5bdd ("riscv: implement Zicbom-based CMO instructions + the t-head variant")
Fixes: 1631ba1259d6 ("riscv: Add support for non-coherent devices using zicbom extension")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
[Conor: fixed the redefinition errors]
Tested-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220912224800.998121-1-mail@conchuod.ie
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

4 files changed, 16 insertions, 11 deletions

diff --git a/arch/riscv/errata/thead/errata.c b/arch/riscv/errata/thead/errata.c
index 202c83f677b2..96648c176f37 100644
--- a/arch/riscv/errata/thead/errata.c
+++ b/arch/riscv/errata/thead/errata.c
@@ -37,6 +37,7 @@ static bool errata_probe_cmo(unsigned int stage,
 	if (stage == RISCV_ALTERNATIVES_EARLY_BOOT)
 		return false;
 
+	riscv_cbom_block_size = L1_CACHE_BYTES;
 	riscv_noncoherent_supported();
 	return true;
 #else
diff --git a/arch/riscv/include/asm/cacheflush.h b/arch/riscv/include/asm/cacheflush.h
index a60acaecfeda..a89c005b4bbf 100644
--- a/arch/riscv/include/asm/cacheflush.h
+++ b/arch/riscv/include/asm/cacheflush.h
@@ -43,6 +43,7 @@ void flush_icache_mm(struct mm_struct *mm, bool local);
 #endif /* CONFIG_SMP */
 
 #ifdef CONFIG_RISCV_ISA_ZICBOM
+extern unsigned int riscv_cbom_block_size;
 void riscv_init_cbom_blocksize(void);
 #else
 static inline void riscv_init_cbom_blocksize(void) { }
diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
index 95ef6e2bf45c..2dfc463b86bb 100644
--- a/arch/riscv/kernel/setup.c
+++ b/arch/riscv/kernel/setup.c
@@ -296,8 +296,8 @@ void __init setup_arch(char **cmdline_p)
 	setup_smp();
 #endif
 
-	riscv_fill_hwcap();
 	riscv_init_cbom_blocksize();
+	riscv_fill_hwcap();
 	apply_boot_alternatives();
 }
 
diff --git a/arch/riscv/mm/dma-noncoherent.c b/arch/riscv/mm/dma-noncoherent.c
index cd2225304c82..e3f9bdf47c5f 100644
--- a/arch/riscv/mm/dma-noncoherent.c
+++ b/arch/riscv/mm/dma-noncoherent.c
@@ -12,7 +12,7 @@
 #include <linux/of_device.h>
 #include <asm/cacheflush.h>
 
-static unsigned int riscv_cbom_block_size = L1_CACHE_BYTES;
+unsigned int riscv_cbom_block_size;
 static bool noncoherent_supported;
 
 void arch_sync_dma_for_device(phys_addr_t paddr, size_t size,
@@ -79,38 +79,41 @@ void arch_setup_dma_ops(struct device *dev, u64 dma_base, u64 size,
 void riscv_init_cbom_blocksize(void)
 {
 	struct device_node *node;
+	unsigned long cbom_hartid;
+	u32 val, probed_block_size;
 	int ret;
-	u32 val;
 
+	probed_block_size = 0;
 	for_each_of_cpu_node(node) {
 		unsigned long hartid;
-		int cbom_hartid;
 
 		ret = riscv_of_processor_hartid(node, &hartid);
 		if (ret)
 			continue;
 
-		if (hartid < 0)
-			continue;
-
 		/* set block-size for cbom extension if available */
 		ret = of_property_read_u32(node, "riscv,cbom-block-size", &val);
 		if (ret)
 			continue;
 
-		if (!riscv_cbom_block_size) {
-			riscv_cbom_block_size = val;
+		if (!probed_block_size) {
+			probed_block_size = val;
 			cbom_hartid = hartid;
 		} else {
-			if (riscv_cbom_block_size != val)
-				pr_warn("cbom-block-size mismatched between harts %d and %lu\n",
+			if (probed_block_size != val)
+				pr_warn("cbom-block-size mismatched between harts %lu and %lu\n",
 					cbom_hartid, hartid);
 		}
 	}
+
+	if (probed_block_size)
+		riscv_cbom_block_size = probed_block_size;
 }
 #endif
 
 void riscv_noncoherent_supported(void)
 {
+	WARN(!riscv_cbom_block_size,
+	     "Non-coherent DMA support enabled without a block size\n");
 	noncoherent_supported = true;
 }