blacklist Samsung Mongoose 3 from ASIMDHP

The big cores on Exynos 9810 (intl. Galaxy S9) are Mongoose 3,
and report to support ASIMDHP but don't (unless you like crashing.)

Tested locally with an intl. Galaxy S9 and a Pixel 3.

See https://en.wikichip.org/wiki/samsung/exynos/9810,
and golang/go#28431 for a similar bug
with the same chip.

Change-Id: Iddb4ff569f216508c5283e32f3411c49cd76fee0
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/215948
Reviewed-by: Herb Derby <[email protected]>
Commit-Queue: Mike Klein <[email protected]>

Author: Mike Klein

src/core/SkCpu.cpp

@@ -5,6 +5,8 @@
  * found in the LICENSE file.
  */
 
+#include "include/core/SkStream.h"
+#include "include/core/SkString.h"
 #include "include/private/SkOnce.h"
 #include "src/core/SkCpu.h"
 
@@ -81,6 +83,34 @@
         uint32_t hwcaps = getauxval(AT_HWCAP);
         if (hwcaps & kHWCAP_CRC32  ) { features |= SkCpu::CRC32; }
         if (hwcaps & kHWCAP_ASIMDHP) { features |= SkCpu::ASIMDHP; }
+
+        // The Samsung Mongoose 3 core sets the ASIMDHP bit but doesn't support it.
+        for (int core = 0; features & SkCpu::ASIMDHP; core++) {
+            // These /sys files contain the core's MIDR_EL1 register, the source of
+            // CPU {implementer, variant, part, revision} you'd see in /proc/cpuinfo.
+            SkString path =
+                SkStringPrintf("/sys/devices/system/cpu/cpu%d/regs/identification/midr_el1", core);
+
+            // Can't use SkData::MakeFromFileName() here, I think because /sys can't be mmap()'d.
+            SkFILEStream midr_el1(path.c_str());
+            if (!midr_el1.isValid()) {
+                // This is our ordinary exit path.
+                // If we ask for MIDR_EL1 from a core that doesn't exist, we've checked all cores.
+                if (core == 0) {
+                    // On the other hand, if we can't read MIDR_EL1 from any core, assume the worst.
+                    features &= ~(SkCpu::ASIMDHP);
+                }
+                break;
+            }
+
+            const char kMongoose3[] = "0x00000000531f0020";  // 53 == Samsung.
+            char buf[SK_ARRAY_COUNT(kMongoose3) - 1];  // No need for the terminating \0.
+
+            if (SK_ARRAY_COUNT(buf) != midr_el1.read(buf, SK_ARRAY_COUNT(buf))
+                          || 0 == memcmp(kMongoose3, buf, SK_ARRAY_COUNT(buf))) {
+                features &= ~(SkCpu::ASIMDHP);
+            }
+        }
         return features;
     }