On 08/09/2017 08:04 PM, Brendan Higgins wrote:
Perhaps that is some level of abuse, but it's pretty common.  I'm not
against it.

There is standard IPMI firmware NetFN (though no commands defined) that if
you use
the driver automatically goes into "Maintenance mode" and modified the
and handling to some extent to help with this.
That is a really good point, I missed that.

There are ways to accomplish this that aren't that complex.  You can create
an OEM
command that can query the maximum message size and the ability to do
numbers in the messages.

If messages larger than 32-bytes are supported, and the host I2C/SMBus
supports it, you could use the standard SSIF SMBus commands to do this, they
have an 8-bit length field.

If sequence numbers are supported, The SSIF could use different SMBus
to do the write and read requests.  Since this is only if you get an OEM
and if you put the sequence numbers at the end where they are easy to add on
the send side, this is a small change to the driver.
What if we just had an OEM command that changed the message structure from
that point on? We could abuse the "maintenance mode" NetFN to get back into
normal SSIF if necessary.

Actually, I wouldn't have a separate "openbmc mode". I would have OpenBMC always
work with standard SSIF, and have separate SMBus commands for messages with
the sequence number and messages larger than 32 bytes.

I've attached a patch with what I would expect the changes to be to the host driver. It doesn't handle multiple outstanding messages, but it shows what detection and a
separate SMBus command would look like.

So I think the changes would be small and contained.  I'm actually ok with a
different driver, but I think it would be more valuable to the OpenBMC
to have a standardized interface that would work (in a not quite as
mode) with software that does not use the Linux IPMI driver.
I guess I see the all of my asks as hacky things which we can hopefully remove
at some point. Hopefully, most OpenBMC users won't want or need these things.
Regardless of what we do with the "BT-I2C" stuff, I am still interested in
you think about this.

I think you are right, it probably belongs some place else.  The way that
makes the most
sense to me would be to have an "ipmi" directory with a "host" and "slave"
side, and since
ipmi is not really a char driver, to move it to the main driver directory.
That might be
fairly disruptive, though.
That was my thinking exactly.

The other option that makes sense to me would be to add a
drivers/char/ipmi_slave directory,
or something like that, and put the slave code there.  That would be less
Right that is the approach I took, except I called it drivers/char/ipmi_bmc.

I originally thought doing the less disruptive thing is best; however, I know
there are also some OpenBMC people who are interested in implementing
IPMB. So maybe now is the time to bite the bullet and create an ipmi
directory under drivers/.

I'm not sure IPMB would make much difference, there's no host side change as it's already supported. I don't think there would be any significant code sharing
between the two.

If there end up being a significant amount of common code, then it would
definitely be worth the effort to move it.

In summary, I think I can live with making it a mangled form of SSIF, but
I would prefer to put it in its own driver.

You can look at the patch and consider it, and consider that you would need to
implement flag and event handling.  On an x86 host there would be SMBIOS
and ACPI stuff to deal with somehow for discovery. There's probably few other
things to deal with.

In any case, I think I would rather focus on the the BMC side IPMI framework
now, since it is a bigger change and would also reduce the work of
implementing a BMC side SSIF driver.

Here is what I propose: we focus on the BMC side IPMI framework RFC that
I sent out the other day:
I will add a change to the BMC side IPMI framework patchset to move all the
IPMI stuff to the new drivers/ipmi directory as discussed and then drop the
patch in that patchset that depends on this patchset.

Let me know what you think

Let's hold off on the new directory, there's probably some convincing of the "powers
that be" for that.

I'll look at the patch set tomorrow, unless something critical comes up.



diff --git a/drivers/char/ipmi/ipmi_ssif.c b/drivers/char/ipmi/ipmi_ssif.c
index 11237e8..d467b1a 100644
--- a/drivers/char/ipmi/ipmi_ssif.c
+++ b/drivers/char/ipmi/ipmi_ssif.c
@@ -60,6 +60,11 @@
+static u8 openbmc_iana[3] = { 0x10, 0x20, 0x30 };
 #define	SSIF_IPMI_REQUEST			2
@@ -224,6 +229,12 @@ struct ssif_info {
 	bool		    supports_alert;
+	 * OpenBMC mode, with large message and sequence number
+	 * support.  An int because we use it as a number, too.
+	 */
+	unsigned int	    is_openbmc;
+	/*
 	 * Used to tell what we should do with alerts.  If we are
 	 * waiting on a response, read the data immediately.
@@ -537,12 +548,13 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 static void start_get(struct ssif_info *ssif_info)
 	int rv;
+	int command = ssif_info->is_openbmc ? SSIF_OPENBMC_RESPONSE :
 	ssif_info->rtc_us_timer = 0;
 	ssif_info->multi_pos = 0;
-	rv = ssif_i2c_send(ssif_info, msg_done_handler, I2C_SMBUS_READ,
+	rv = ssif_i2c_send(ssif_info, msg_done_handler, I2C_SMBUS_READ, command,
 			  ssif_info->recv, I2C_SMBUS_BLOCK_DATA);
 	if (rv < 0) {
 		/* request failed, just return the error. */
@@ -611,7 +623,8 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 	 * start messing with driver states or the queues.
-	if (result < 0) {
+	if (result < 0 || len < 3) {
+	ignore_msg:
 		if (ssif_info->retries_left > 0) {
 			ssif_inc_stat(ssif_info, receive_retries);
@@ -633,7 +646,13 @@ static void msg_done_handler(struct ssif_info *ssif_info, int result,
 		goto continue_op;
-	if ((len > 1) && (ssif_info->multi_pos == 0)
+	if (ssif_info->is_openbmc) {
+		if (len < 4)
+			goto ignore_msg;
+		/* Eventually extract sequence number from data[0]. */
+		data++;
+		len--;
+	} else if ((len > 1) && (ssif_info->multi_pos == 0)
 				&& (data[0] == 0x00) && (data[1] == 0x01)) {
 		/* Start of multi-part read.  Start the next transaction. */
 		int i;
@@ -966,7 +985,11 @@ static int start_resend(struct ssif_info *ssif_info)
 	ssif_info->got_alert = false;
-	if (ssif_info->data_len > 32) {
+	if (ssif_info->is_openbmc) {
+		ssif_info->multi_data = NULL;
+		ssif_info->data[0] = ssif_info->data_len;
+	} else if (ssif_info->data_len > 32) {
 		ssif_info->multi_data = ssif_info->data;
 		ssif_info->multi_len = ssif_info->data_len;
@@ -1000,7 +1023,11 @@ static int start_send(struct ssif_info *ssif_info,
 		return -E2BIG;
 	ssif_info->retries_left = SSIF_SEND_RETRIES;
-	memcpy(ssif_info->data + 1, data, len);
+	memcpy(ssif_info->data + 1 + ssif_info->is_openbmc, data, len);
+	if (ssif_info->is_openbmc) {
+		ssif_info->data[1] = 0; /* Sequence number eventually. */
+		len++;
+	}
 	ssif_info->data_len = len;
 	return start_resend(ssif_info);
@@ -1507,7 +1534,7 @@ static struct ipmi_fw_revision_range ssif_broken_alert_bmcs[] = {
 static int ssif_probe(struct i2c_client *client, const struct i2c_device_id *id)
-	unsigned char     msg[3];
+	unsigned char     msg[6];
 	unsigned char     *resp;
 	struct ssif_info   *ssif_info;
 	int               rv = 0;
@@ -1643,6 +1670,24 @@ static int ssif_probe(struct i2c_client *client, const struct i2c_device_id *id)
 		ssif_info->supports_pec = 0;
+	memcpy(msg, openbmc_iana, sizeof(openbmc_iana));
+	rv = do_cmd(client, 5, msg, &len, resp);
+	if (!rv && (len >= 3) && (resp[2] == 0)) {
+		/* It appears we have an OpenBMC device. */
+		/* Turn of multi support. */
+		ssif_info->multi_support = SSIF_NO_MULTI;
+		ssif_info->max_xmit_msg_size = 32;
+		ssif_info->max_recv_msg_size = 32;
+		if (len > 3)
+			ssif_info->max_xmit_msg_size = resp[3];
+		if (len > 4)
+			ssif_info->max_recv_msg_size = resp[4];
+		ssif_info->is_openbmc = 1;
+	}
 	/* Make sure the NMI timeout is cleared. */
 	msg[0] = IPMI_NETFN_APP_REQUEST << 2;
diff --git a/include/uapi/linux/ipmi_msgdefs.h b/include/uapi/linux/ipmi_msgdefs.h
index df97e6e..bb0af2e 100644
--- a/include/uapi/linux/ipmi_msgdefs.h
+++ b/include/uapi/linux/ipmi_msgdefs.h
@@ -71,6 +71,9 @@
 /* The default slave address */
 #define IPMI_BMC_SLAVE_ADDR	0x20
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