[v2,4/4] core/flash: Make opal_flash_op() actually asynchronous

Message ID 20170711060639.960-4-cyril.bur@au1.ibm.com
State New
Headers show

Commit Message

Cyril Bur July 11, 2017, 6:06 a.m.
This patch provides a simple (although not particularly efficient)
asynchronous capability to the opal_flash interface. The advantage of
this approach is that it doesn't require any changing of blocklevel or
its backends to provide an asynchronous implementation. This is also the
disadvantage of this implementation as all it actually does is break the
work up in chunks that it can performed quickly, but still
synchronously. Only a backend could provide a more asynchronous
implementation.

This solves a problem we have right now with the opal_flash_erase call
where it can block in Skiboot for around three minutes. This causes a
variety of problems in Linux due to a processor being gone for a long
time.
For example:

[   98.610043] INFO: rcu_sched detected stalls on CPUs/tasks:
[   98.610050]         113-...: (1 GPs behind) idle=96f/140000000000000/0 softirq=527/528 fqs=1044
[   98.610051]         (detected by 112, t=2102 jiffies, g=223, c=222, q=123)
[   98.610060] Task dump for CPU 113:
[   98.610062] pflash          R  running task        0  3335   3333 0x00040004
[   98.610066] Call Trace:
[   98.610070] [c000001fdd847730] [0000000000000001] 0x1 (unreliable)
[   98.610076] [c000001fdd847900] [c000000000013854] __switch_to+0x1e8/0x1f4
[   98.610081] [c000001fdd847960] [c0000000006122c4] __schedule+0x32c/0x874
[   98.610083] [c000001fdd847a30] [c000001fdd847b40] 0xc000001fdd847b40

It is for this reason that breaking the work up in smaller chunks solves
this problem as Skiboot can return the CPU to Linux between chunks to
avoid Linux getting upset.

Reported-By: Samuel Mendoza-Jonas <sam@mendozajonas.com>
Signed-off-by: Cyril Bur <cyril.bur@au1.ibm.com>
---
V2: Use the second suggestion after Alistair didn't like v1
    Refactored the code from what was initially sent

 core/flash.c                            | 136 ++++++++++++++++++++++----------
 doc/opal-api/opal-flash-110-111-112.rst |   4 +
 2 files changed, 100 insertions(+), 40 deletions(-)

Patch

diff --git a/core/flash.c b/core/flash.c
index 177f7ae1..f953490e 100644
--- a/core/flash.c
+++ b/core/flash.c
@@ -28,6 +28,23 @@ 
 #include <libstb/stb.h>
 #include <libstb/container.h>
 #include <elf.h>
+#include <timer.h>
+#include <timebase.h>
+
+enum flash_op {
+	FLASH_OP_READ,
+	FLASH_OP_WRITE,
+	FLASH_OP_ERASE,
+};
+
+struct flash_async_info {
+	enum flash_op op;
+	struct timer poller;
+	uint64_t token;
+	uint64_t pos;
+	uint64_t len;
+	uint64_t buf;
+};
 
 struct flash {
 	struct list_node	list;
@@ -36,6 +53,7 @@  struct flash {
 	uint64_t		size;
 	uint32_t		block_size;
 	int			id;
+	struct flash_async_info async;
 };
 
 static LIST_HEAD(flashes);
@@ -263,6 +281,64 @@  static int num_flashes(void)
 	return i;
 }
 
+/*
+ * Called with flash lock held, drop it on async completion
+ */
+static void flash_poll(struct timer *t __unused, void *data,
+		uint64_t now __unused)
+{
+	struct flash *flash = data;
+	uint64_t len;
+	int rc;
+
+	len = MIN(flash->async.len, flash->block_size);
+
+	/*
+	 * These ops intentionally have no smarts (ecc correction or erase
+	 * before write) to them.
+	 * Skiboot is simply exposing the PNOR flash to the host.
+	 * The host is expected to understand that this is a raw flash
+	 * device and treat it as such.
+	 */
+
+	switch (flash->async.op) {
+	case FLASH_OP_READ:
+		rc = blocklevel_raw_read(flash->bl, flash->async.pos,
+				(void *)flash->async.buf, len);
+		break;
+	case FLASH_OP_WRITE:
+		rc = blocklevel_raw_write(flash->bl, flash->async.pos,
+				(void *)flash->async.buf, len);
+		break;
+	case FLASH_OP_ERASE:
+		rc = blocklevel_erase(flash->bl, flash->async.pos, len);
+		break;
+	default:
+		assert(0);
+	}
+
+	if (rc) {
+		rc = OPAL_HARDWARE;
+		goto out;
+	}
+
+	flash->async.pos += len;
+	flash->async.buf += len;
+	flash->async.len -= len;
+	if (flash->async.len) {
+		/*
+		 * We want to get called pretty much straight away, just have
+		 * to be sure that we jump back out to Linux so that we don't
+		 * cause RCU or the scheduler to freak.
+		 */
+		schedule_timer(&flash->async.poller, msecs_to_tb(1));
+		return;
+	}
+out:
+	opal_queue_msg(OPAL_MSG_ASYNC_COMP, NULL, NULL, flash->async.token, rc);
+	flash_release(flash);
+}
+
 int flash_register(struct blocklevel_device *bl)
 {
 	uint64_t size;
@@ -295,6 +371,7 @@  int flash_register(struct blocklevel_device *bl)
 	flash->size = size;
 	flash->block_size = block_size;
 	flash->id = num_flashes();
+	init_timer(&flash->async.poller, flash_poll, flash);
 
 	list_add(&flashes, &flash->list);
 
@@ -323,17 +400,10 @@  int flash_register(struct blocklevel_device *bl)
 	return OPAL_SUCCESS;
 }
 
-enum flash_op {
-	FLASH_OP_READ,
-	FLASH_OP_WRITE,
-	FLASH_OP_ERASE,
-};
-
 static int64_t opal_flash_op(enum flash_op op, uint64_t id, uint64_t offset,
 		uint64_t buf, uint64_t size, uint64_t token)
 {
 	struct flash *flash = NULL;
-	int rc;
 
 	list_for_each(&flashes, flash, list)
 		if (flash->id == id)
@@ -350,44 +420,30 @@  static int64_t opal_flash_op(enum flash_op op, uint64_t id, uint64_t offset,
 			|| offset + size > flash->size) {
 		prlog(PR_DEBUG, "Requested flash op %d beyond flash size %" PRIu64 "\n",
 				op, flash->size);
-		rc = OPAL_PARAMETER;
-		goto err;
-	}
-
-	/*
-	 * These ops intentionally have no smarts (ecc correction or erase
-	 * before write) to them.
-	 * Skiboot is simply exposing the PNOR flash to the host.
-	 * The host is expected to understand that this is a raw flash
-	 * device and treat it as such.
-	 */
-	switch (op) {
-	case FLASH_OP_READ:
-		rc = blocklevel_raw_read(flash->bl, offset, (void *)buf, size);
-		break;
-	case FLASH_OP_WRITE:
-		rc = blocklevel_raw_write(flash->bl, offset, (void *)buf, size);
-		break;
-	case FLASH_OP_ERASE:
-		rc = blocklevel_erase(flash->bl, offset, size);
-		break;
-	default:
-		assert(0);
+		flash_release(flash);
+		return OPAL_PARAMETER;
 	}
 
-	if (rc) {
-		rc = OPAL_HARDWARE;
-		goto err;
-	}
+	flash->async.token = token;
+	flash->async.op = op;
+	flash->async.pos = offset;
+	flash->async.buf = buf;
+	flash->async.len = size;
 
-	flash_release(flash);
+	/* Kick off the process */
+	flash_poll(&flash->async.poller, flash, mftb());
 
-	opal_queue_msg(OPAL_MSG_ASYNC_COMP, NULL, NULL, token, rc);
+	/*
+	 * As of 1/07/2017 the powernv_flash driver in Linux will handle
+	 * OPAL_SUCCESS as an error, the only thing that makes it handle
+	 * things as though they're working is receiving
+	 * OPAL_ASYNC_COMPLETION.
+	 *
+	 * This pretty much rules out any optimisation where the required
+	 * work could be done stright away with no need for
+	 * OPAL_ASYNC_COMPLETION. Oh well.
+	 */
 	return OPAL_ASYNC_COMPLETION;
-
-err:
-	flash_release(flash);
-	return rc;
 }
 
 static int64_t opal_flash_read(uint64_t id, uint64_t offset, uint64_t buf,
diff --git a/doc/opal-api/opal-flash-110-111-112.rst b/doc/opal-api/opal-flash-110-111-112.rst
index 71ba866d..086c4095 100644
--- a/doc/opal-api/opal-flash-110-111-112.rst
+++ b/doc/opal-api/opal-flash-110-111-112.rst
@@ -20,6 +20,10 @@  success, the calls will return ``OPAL_ASYNC_COMPLETION``, and an
 opal_async_completion message will be sent (with the appropriate token
 argument) when the operation completes.
 
+Due to an error in the powernv_flash driver in Linux these three OPAL
+calls should never return ``OPAL_SUCCESS`` as the driver is likely to
+treat this return value as an error.
+
 All calls share the same return values:
 
 ``OPAL_ASYNC_COMPLETION``