[PATCH] crypto: x86/crc32c-intel - Don't match some Zhaoxin CPUs

[Tony W Wang-oc]

The driver crc32c-intel match CPUs supporting X86_FEATURE_XMM4_2.
On platforms with Zhaoxin CPUs supporting this X86 feature, when
crc32c-intel and crc32c-generic are both registered, system will
use crc32c-intel because its .cra_priority is greater than
crc32c-generic.

When doing lmbench3 Create and Delete file test on partitions with
ext4 enabling metadata checksum, found using crc32c-generic driver
could get about 20% performance gain than using the driver crc32c-intel
on some Zhaoxin CPUs.

This case expect to use crc32c-generic driver for these Zhaoxin CPUs
to get performance gain, so remove these Zhaoxin CPUs support from
crc32c-intel.

Signed-off-by: Tony W Wang-oc <TonyWWang-oc@xxxxxxxxxxx>
---
 arch/x86/crypto/crc32c-intel_glue.c | 21 +++++++++++++++++++--
 1 file changed, 19 insertions(+), 2 deletions(-)

diff --git a/arch/x86/crypto/crc32c-intel_glue.c b/arch/x86/crypto/crc32c-intel_glue.c
index feccb52..5171091 100644
--- a/arch/x86/crypto/crc32c-intel_glue.c
+++ b/arch/x86/crypto/crc32c-intel_glue.c
@@ -215,14 +215,31 @@ static struct shash_alg alg = {
 };
 
 static const struct x86_cpu_id crc32c_cpu_id[] = {
-	X86_MATCH_FEATURE(X86_FEATURE_XMM4_2, NULL),
+	/*
+	 * Negative entries; exclude these chips from using this driver.
+	 * They match the positive rule below, but their CRC32 instruction
+	 * implementation is so slow, it doesn't merit use.
+	 */
+	X86_MATCH_VENDOR_FAM_FEATURE(ZHAOXIN, 0x6, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(ZHAOXIN, 0x7, 0x1b, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(ZHAOXIN, 0x7, 0x3b, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_FEATURE(CENTAUR, 0x6, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(CENTAUR, 0x7, 0x1b, X86_FEATURE_XMM4_2, false),
+	X86_MATCH_VENDOR_FAM_MODEL_FEATURE(CENTAUR, 0x7, 0x3b, X86_FEATURE_XMM4_2, false),
+	/*
+	 * Positive entry; SSE-4.2 instructions include special purpose CRC32
+	 * instructions.
+	 */
+	X86_MATCH_FEATURE(X86_FEATURE_XMM4_2, true),
 	{}
 };
 MODULE_DEVICE_TABLE(x86cpu, crc32c_cpu_id);
 
 static int __init crc32c_intel_mod_init(void)
 {
-	if (!x86_match_cpu(crc32c_cpu_id))
+	const struct x86_cpu_id *m = x86_match_cpu(crc32c_cpu_id);
+
+	if (!m || !m->driver_data)
 		return -ENODEV;
 #ifdef CONFIG_X86_64
 	if (boot_cpu_has(X86_FEATURE_PCLMULQDQ)) {
-- 
2.7.4