Prevent the compiler from caching reads/writes to the hw register as we
do want to perform mmio.

Whilst fixing up the mmio access, also ensure that we do not leave the
test with any other bits still set in the forcewake register to prevent
affecting other tests, as spotted by Tvrtko.

Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
---
Also be sure the compiler doesn't eliminate t->done.
Go get some coffee Chris.
-Chris
 tests/gen7_forcewake_mt.c | 59 +++++++++++++++++++++++++++++++++++++----------
 1 file changed, 47 insertions(+), 12 deletions(-)

diff --git a/tests/gen7_forcewake_mt.c b/tests/gen7_forcewake_mt.c
index 07320ef9..6eb66c00 100644
--- a/tests/gen7_forcewake_mt.c
+++ b/tests/gen7_forcewake_mt.c
@@ -41,12 +41,14 @@ IGT_TEST_DESCRIPTION("Exercise a suspect workaround 
required for"
                     " FORCEWAKE_MT.");
 
 #define FORCEWAKE_MT 0xa188
+#define READ_ONCE(x) (*(volatile typeof(x) *)(&(x)))
 
 struct thread {
        pthread_t thread;
-       void *mmio;
+       volatile uint32_t *mmio;
        int fd;
        int bit;
+       bool done;
 };
 
 static const struct pci_id_match match[] = {
@@ -80,7 +82,7 @@ static struct pci_device *__igfx_get(void)
        return dev;
 }
 
-static void *igfx_get_mmio(void)
+static volatile uint32_t *igfx_get_forcewake_mt(void)
 {
        struct pci_device *pci = __igfx_get();
        void *mmio = NULL;
@@ -100,20 +102,27 @@ static void *igfx_get_mmio(void)
        igt_assert_eq(error, 0);
        igt_assert(mmio != NULL);
 
-       return mmio;
+       return (volatile uint32_t *)((char *)mmio + FORCEWAKE_MT);
 }
 
+
 static void *thread(void *arg)
 {
+       static const char acquire_error[] = "acquire";
+       static const char release_error[] = "release";
+
        struct thread *t = arg;
-       uint32_t *forcewake_mt = (uint32_t *)((char *)t->mmio + FORCEWAKE_MT);
-       uint32_t bit = 1 << t->bit;
+       const uint32_t bit = 1 << t->bit;
+       volatile uint32_t *forcewake_mt = t->mmio;
 
-       while (1) {
+       while (!READ_ONCE(t->done)) {
                *forcewake_mt = bit << 16 | bit;
-               igt_assert(*forcewake_mt & bit);
+               if (igt_wait(*forcewake_mt & bit, 50, 1))
+                       return (void *)acquire_error;
+
                *forcewake_mt = bit << 16;
-               igt_assert((*forcewake_mt & bit) == 0);
+               if (igt_wait((*forcewake_mt & bit) == 0, 50, 1))
+                       return (void *)release_error;
        }
 
        return NULL;
@@ -124,10 +133,12 @@ static void *thread(void *arg)
 igt_simple_main
 {
        struct thread t[16];
+       bool success = true;
        int i;
 
        t[0].fd = drm_open_driver(DRIVER_INTEL);
-       t[0].mmio = igfx_get_mmio();
+       t[0].mmio = igfx_get_forcewake_mt();
+       t[0].done = false;
 
        for (i = 2; i < 16; i++) {
                t[i] = t[0];
@@ -137,7 +148,7 @@ igt_simple_main
 
        sleep(2);
 
-       for (i = 0; i < 1000; i++) {
+       igt_until_timeout(2) {
                uint32_t *p;
                struct drm_i915_gem_execbuffer2 execbuf;
                struct drm_i915_gem_exec_object2 exec[2];
@@ -192,13 +203,37 @@ igt_simple_main
                p = gem_mmap__gtt(t[0].fd, exec[0].handle, 4096, PROT_READ);
 
                igt_info("[%d]={ %08x %08x }\n", i, p[0], p[1]);
-               igt_assert(p[0] & 2);
-               igt_assert((p[1] & 2) == 0);
+               if ((p[0] & 2) == 0) {
+                       igt_warn("Failed to acquire forcewake BIT(1) from 
batch\n");
+                       success = false;
+               }
+               if ((p[1] & 2)) {
+                       igt_warn("Failed to release forcewake BIT(1) from 
batch\n");
+                       success = false;
+               }
 
                munmap(p, 4096);
                gem_close(t[0].fd, exec[0].handle);
                gem_close(t[0].fd, exec[1].handle);
+               if (!success)
+                       break;
 
                usleep(1000);
        }
+
+       for (i = 2; i < 16; i++) {
+               void *result;
+
+               t[i].done = true;
+               pthread_join(t[i].thread, &result);
+               if (result) {
+                       igt_warn("Thread BIT(%d) failed to %s forcewake\n", i, 
(char *)result);
+                       success = false;
+               }
+       }
+
+       /* And clear all forcewake bits before disappearing */
+       *t[0].mmio = 0xfffe << 16;
+
+       igt_assert(success);
 }
-- 
2.16.2

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