Convert vboot hash calculation from task to deferred function

Vboot hash calculation takes ~350 ms during EC boot.  Since the hash
task is higher priority than the hook task, this starves all the hooks
during boot.

We could, in theory, fix that simply by swapping the priority of the
hook and hash tasks.  But then watchdog detection (in the hook task)
wouldn't detect hangs in the hash task.

A better fix (implemented here) is to convert the hashing operation to
a series of deferred function calls.  This gets rid of the hash task
entirely, and allows all pending hooks and other deferred function
calls to take place between each chunk of hashing.

On STM32-based boards, we need to bump up the hook task stack size,
since hashing is called from several layers deep in the hook task
instead of at the top of its own task, but this is still a net win of
several hundred bytes of SRAM.

BUG=chrome-os-partner:24892
BRANCH=rambi
TEST=Boot EC; look for "hash start" and "hash done" debug output.
     'taskinfo' shows at least 32 bytes of unused stack for HOOKS task.
     'hash ro' runs properly from EC console.

Change-Id: I9e580dc10fc0bc8e44896d84451218ef67578bbe
Signed-off-by: Randall Spangler <rspangler@chromium.org>
Reviewed-on: https://chromium-review.googlesource.com/181954

3 files changed, 86 insertions, 85 deletions

diff --git a/common/build.mk b/common/build.mk
index b1ac341891..21814a5d83 100644
--- a/common/build.mk
+++ b/common/build.mk
@@ -54,11 +54,11 @@ common-$(CONFIG_SWITCH)+=switch.o
 common-$(CONFIG_TEMP_SENSOR)+=temp_sensor.o thermal.o
 common-$(CONFIG_USB_PORT_POWER_DUMB)+=usb_port_power_dumb.o
 common-$(CONFIG_USB_PORT_POWER_SMART)+=usb_port_power_smart.o
+common-$(CONFIG_VBOOT_HASH)+=sha256.o vboot_hash.o
 common-$(CONFIG_WIRELESS)+=wireless.o
 common-$(HAS_TASK_CHIPSET)+=chipset.o throttle_ap.o
 common-$(HAS_TASK_CONSOLE)+=console.o
 common-$(HAS_TASK_HOSTCMD)+=acpi.o host_command.o host_event_commands.o
 common-$(HAS_TASK_KEYSCAN)+=keyboard_scan.o
 common-$(HAS_TASK_LIGHTBAR)+=lightbar.o
-common-$(HAS_TASK_VBOOTHASH)+=sha256.o vboot_hash.o
 common-$(TEST_BUILD)+=test_util.o
diff --git a/common/flash.c b/common/flash.c
index ccb0827806..10dda3768b 100644
--- a/common/flash.c
+++ b/common/flash.c
@@ -132,7 +132,7 @@ int flash_write(int offset, int size, const char *data)
 	if (flash_dataptr(offset, size, CONFIG_FLASH_WRITE_SIZE, NULL) < 0)
 		return EC_ERROR_INVAL;  /* Invalid range */
 
-#ifdef HAS_TASK_VBOOTHASH
+#ifdef CONFIG_VBOOT_HASH
 	vboot_hash_invalidate(offset, size);
 #endif
 
@@ -144,7 +144,7 @@ int flash_erase(int offset, int size)
 	if (flash_dataptr(offset, size, CONFIG_FLASH_ERASE_SIZE, NULL) < 0)
 		return EC_ERROR_INVAL;  /* Invalid range */
 
-#ifdef HAS_TASK_VBOOTHASH
+#ifdef CONFIG_VBOOT_HASH
 	vboot_hash_invalidate(offset, size);
 #endif
 
diff --git a/common/vboot_hash.c b/common/vboot_hash.c
index abc67ebe00..bd80fbde2d 100644
--- a/common/vboot_hash.c
+++ b/common/vboot_hash.c
@@ -28,7 +28,9 @@ struct vboot_hash_tag {
 
 #define VBOOT_HASH_SYSJUMP_TAG 0x5648 /* "VH" */
 #define VBOOT_HASH_SYSJUMP_VERSION 1
-#define CHUNK_SIZE 1024
+
+#define CHUNK_SIZE 1024       /* Bytes to hash per deferred call */
+#define WORK_INTERVAL_US 100  /* Delay between deferred calls */
 
 static uint32_t data_offset;
 static uint32_t data_size;
@@ -39,10 +41,65 @@ static int in_progress;
 
 static struct sha256_ctx ctx;
 
-/*
+/**
+ * Abort hash currently in progress, and invalidate any completed hash.
+ */
+static void vboot_hash_abort(void)
+{
+	if (in_progress) {
+		want_abort = 1;
+	} else {
+		CPRINTF("[%T hash abort]\n");
+		want_abort = 0;
+		data_size = 0;
+		hash = NULL;
+	}
+}
+
+/**
+ * Do next chunk of hashing work, if any.
+ */
+static void vboot_hash_next_chunk(void)
+{
+	int size;
+
+	/* Handle abort */
+	if (want_abort) {
+		in_progress = 0;
+		vboot_hash_abort();
+		return;
+	}
+
+	/* Compute the next chunk of hash */
+	size = MIN(CHUNK_SIZE, data_size - curr_pos);
+	SHA256_update(&ctx, (const uint8_t *)(CONFIG_FLASH_BASE +
+					      data_offset + curr_pos), size);
+
+	curr_pos += size;
+	if (curr_pos >= data_size) {
+		/* Store the final hash */
+		hash = SHA256_final(&ctx);
+		CPRINTF("[%T hash done %.*h]\n", SHA256_DIGEST_SIZE, hash);
+
+		in_progress = 0;
+
+		/* Handle receiving abort during finalize */
+		if (want_abort)
+			vboot_hash_abort();
+
+		return;
+	}
+
+	/* If we're still here, more work to do; come back later */
+	hook_call_deferred(vboot_hash_next_chunk, WORK_INTERVAL_US);
+}
+DECLARE_DEFERRED(vboot_hash_next_chunk);
+
+/**
  * Start computing a hash of <size> bytes of data at flash offset <offset>.
- * If nonce_size is non-zero, prefixes the <nonce> onto the data to be
- * hashed.  Returns non-zero if error.
+ *
+ * If nonce_size is non-zero, prefixes the <nonce> onto the data to be hashed.
+ * Returns non-zero if error.
  */
 static int vboot_hash_start(uint32_t offset, uint32_t size,
 			    const uint8_t *nonce, int nonce_size)
@@ -74,25 +131,34 @@ static int vboot_hash_start(uint32_t offset, uint32_t size,
 	if (nonce_size)
 		SHA256_update(&ctx, nonce, nonce_size);
 
-	/* Wake the hash task */
-	task_wake(TASK_ID_VBOOTHASH);
+	hook_call_deferred(vboot_hash_next_chunk, 0);
 
 	return EC_SUCCESS;
 }
 
-/* Abort hash currently in progress, and invalidate any completed hash. */
-static void vboot_hash_abort(void)
+int vboot_hash_invalidate(int offset, int size)
 {
-	if (in_progress) {
-		want_abort = 1;
-	} else {
-		CPRINTF("[%T hash abort]\n");
-		want_abort = 0;
-		data_size = 0;
-		hash = NULL;
-	}
+	/* Don't invalidate if passed an invalid region */
+	if (offset < 0 || size <= 0 || offset + size < 0)
+		return 0;
+
+	/* Don't invalidate if hash is already invalid */
+	if (!hash)
+		return 0;
+
+	/* No overlap if passed region is off either end of hashed region */
+	if (offset + size <= data_offset || offset >= data_offset + data_size)
+		return 0;
+
+	/* Invalidate the hash */
+	CPRINTF("[%T hash invalidated 0x%08x 0x%08x]\n", offset, size);
+	vboot_hash_abort();
+	return 1;
 }
 
+/*****************************************************************************/
+/* Hooks */
+
 static void vboot_hash_init(void)
 {
 #ifdef CONFIG_SAVE_VBOOT_HASH
@@ -117,72 +183,7 @@ static void vboot_hash_init(void)
 				 NULL, 0);
 	}
 }
-
-int vboot_hash_invalidate(int offset, int size)
-{
-	/* Don't invalidate if passed an invalid region */
-	if (offset < 0 || size <= 0 || offset + size < 0)
-		return 0;
-
-	/* Don't invalidate if hash is already invalid */
-	if (!hash)
-		return 0;
-
-	/* No overlap if passed region is off either end of hashed region */
-	if (offset + size <= data_offset || offset >= data_offset + data_size)
-		return 0;
-
-	/* Invalidate the hash */
-	CPRINTF("[%T hash invalidated 0x%08x 0x%08x]\n", offset, size);
-	vboot_hash_abort();
-	return 1;
-}
-
-void vboot_hash_task(void)
-{
-	vboot_hash_init();
-
-	while (1) {
-		if (!in_progress) {
-			/* Nothing to do, so go back to sleep */
-			task_wait_event(-1);
-		} else if (want_abort) {
-			/* Abort hash computation currently in progress */
-			in_progress = 0;
-			vboot_hash_abort();
-		} else {
-			/* Compute the next chunk of hash */
-			int size = MIN(CHUNK_SIZE, data_size - curr_pos);
-
-			SHA256_update(&ctx,
-				      (const uint8_t *)(CONFIG_FLASH_BASE +
-							data_offset + curr_pos),
-				      size);
-			curr_pos += size;
-			if (curr_pos >= data_size) {
-				/* Store the final hash */
-				hash = SHA256_final(&ctx);
-				CPRINTF("[%T hash done %.*h]\n",
-					SHA256_DIGEST_SIZE, hash);
-
-				in_progress = 0;
-
-				/* Handle receiving abort during finalize */
-				if (want_abort)
-					vboot_hash_abort();
-			}
-
-			/*
-			 * Let other tasks (really, just the watchdog task)
-			 * run for a bit.
-			 */
-			usleep(100);
-		}
-	}
-}
-
-/*****************************************************************************/
-/* Hooks */
+DECLARE_HOOK(HOOK_INIT, vboot_hash_init, HOOK_PRIO_DEFAULT);
 
 #ifdef CONFIG_SAVE_VBOOT_HASH