Re: [PATCH 1/4] mailbox: add support for System Control and Power Interface(SCPI) protocol
From: Sudeep Holla
Date: Wed Apr 29 2015 - 06:54:09 EST
On 28/04/15 14:54, Jon Medhurst (Tixy) wrote:
On Mon, 2015-04-27 at 12:40 +0100, Sudeep Holla wrote:
This patch adds support for System Control and Power Interface (SCPI)
Message Protocol used between the Application Cores(AP) and the System
Control Processor(SCP). The MHU peripheral provides a mechanism for
inter-processor communication between SCP's M3 processor and AP.
SCP offers control and management of the core/cluster power states,
various power domain DVFS including the core/cluster, certain system
clocks configuration, thermal sensors and many others.
This protocol driver provides interface for all the client drivers using
SCPI to make use of the features offered by the SCP.
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
Cc: Rob Herring <robh+dt@xxxxxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
CC: Jassi Brar <jassisinghbrar@xxxxxxxxx>
Cc: Liviu Dudau <Liviu.Dudau@xxxxxxx>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Jon Medhurst (Tixy) <tixy@xxxxxxxxxx>
Cc: devicetree@xxxxxxxxxxxxxxx
---
There are several spelling errors but I won't point out each, sure you
can find them with a spellcheck ;-) I'll just comment on the code...
OK :)
[...]
+++ b/drivers/mailbox/scpi_protocol.c
@@ -0,0 +1,694 @@
+/*
+ * System Control and Power Interface (SCPI) Message Protocol driver
+ *
+ * SCPI Message Protocol is used between the System Control Processor(SCP)
+ * and the Application Processors(AP). The Message Handling Unit(MHU)
+ * provides a mechanism for inter-processor communication between SCP's
+ * Cortex M3 and AP.
+ *
+ * SCP offers control and management of the core/cluster power states,
+ * various power domain DVFS including the core/cluster, certain system
+ * clocks configuration, thermal sensors and many others.
+ *
+ * Copyright (C) 2015 ARM Ltd.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms and conditions of the GNU General Public License,
+ * version 2, as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program. If not, see <http://www.gnu.org/licenses/>.
+ */
+
[...]
+
+static inline int scpi_to_linux_errno(int errno)
+{
+ if (errno >= SCPI_SUCCESS && errno < SCPI_ERR_MAX)
+ return scpi_linux_errmap[errno];
+ return -EIO;
+}
+
+static void scpi_process_cmd(struct scpi_chan *ch, u32 cmd)
+{
+ unsigned long flags;
+ struct scpi_xfer *t, *match = NULL;
+
+ spin_lock_irqsave(&ch->rx_lock, flags);
+ if (list_empty(&ch->rx_pending)) {
+ spin_unlock_irqrestore(&ch->rx_lock, flags);
+ return;
+ }
+
+ list_for_each_entry(t, &ch->rx_pending, node)
+ if (CMD_XTRACT_UNIQ(t->cmd) == CMD_XTRACT_UNIQ(cmd)) {
So if UNIQ here isn't actually unique amongst all pending requests, its
possible we'll pick the wrong one. There's a couple of scenarios where
that can happen, comments further down about that.
+ list_del(&t->node);
+ match = t;
+ break;
+ }
+ /* check if wait_for_completion is in progress or timed-out */
+ if (match && !completion_done(&match->done)) {
+ struct scpi_shared_mem *mem = ch->rx_payload;
+
+ match->status = le32_to_cpu(mem->status);
+ memcpy_fromio(match->rx_buf, mem->payload, CMD_SIZE(cmd));
+ complete(&match->done);
+ }
+ spin_unlock_irqrestore(&ch->rx_lock, flags);
+}
+
+static void scpi_handle_remote_msg(struct mbox_client *c, void *msg)
+{
+ struct scpi_chan *ch = container_of(c, struct scpi_chan, cl);
+ struct scpi_shared_mem *mem = ch->rx_payload;
+ u32 cmd = le32_to_cpu(mem->command);
+
+ scpi_process_cmd(ch, cmd);
+}
+
+static void scpi_tx_prepare(struct mbox_client *c, void *msg)
+{
+ unsigned long flags;
+ struct scpi_xfer *t = msg;
+ struct scpi_chan *ch = container_of(c, struct scpi_chan, cl);
+ struct scpi_shared_mem *mem = (struct scpi_shared_mem *)ch->tx_payload;
+
+ mem->command = cpu_to_le32(t->cmd);
+ if (t->tx_buf)
+ memcpy_toio(mem->payload, t->tx_buf, t->tx_len);
+ if (t->rx_buf) {
+ spin_lock_irqsave(&ch->rx_lock, flags);
+ list_add_tail(&t->node, &ch->rx_pending);
+ spin_unlock_irqrestore(&ch->rx_lock, flags);
+ }
+}
+
+static struct scpi_xfer *get_scpi_xfer(struct scpi_chan *ch)
+{
+ struct scpi_xfer *t;
+
+ mutex_lock(&ch->xfers_lock);
+ if (list_empty(&ch->xfers_list)) {
+ mutex_unlock(&ch->xfers_lock);
+ return NULL;
+ }
+ t = list_first_entry(&ch->xfers_list, struct scpi_xfer, node);
+ list_del(&t->node);
+ mutex_unlock(&ch->xfers_lock);
+ return t;
+}
+
+static void put_scpi_xfer(struct scpi_xfer *t, struct scpi_chan *ch)
+{
+ mutex_lock(&ch->xfers_lock);
+ list_add_tail(&t->node, &ch->xfers_list);
+ mutex_unlock(&ch->xfers_lock);
+}
+
+static int
+scpi_send_message(u8 cmd, void *tx_buf, unsigned int len, void *rx_buf)
+{
So the caller doesn't specify the length of rx_buf, wouldn't this be a
good idea?
That way we could truncate data sent from the SCP which would prevent
buffer overruns due to buggy SCP or Linux code. It would also allow the
SCP message format to be extended in the future in a backwards
compatible way.
And we could zero fill any data that was too short to allow
compatibility with Linux drivers using any new extended format messages
on older SCP firmware. Or at least so any bugs behave more consistently
by seeing zeros instead of random data left over from old messages.
Make sense, will add len in next version.
+ int ret;
+ u8 token, chan;
+ struct scpi_xfer *msg;
+ struct scpi_chan *scpi_chan;
+
+ chan = atomic_inc_return(&scpi_info->next_chan) % scpi_info->num_chans;
+ scpi_chan = scpi_info->channels + chan;
+
+ msg = get_scpi_xfer(scpi_chan);
+ if (!msg)
+ return -ENOMEM;
+
+ token = atomic_inc_return(&scpi_chan->token) & CMD_TOKEN_ID_MASK;
So, this 8 bit token is what's used to 'uniquely' identify a pending
command. But as it's just an incrementing value, then if one command
gets delayed for long enough that 256 more are issued then we will have
a non-unique value and scpi_process_cmd can go wrong.
IMO by the time 256 message are queued up and serviced we would timeout
on the initial command. Moreover the core mailbox has sent the mailbox
length to 20(MBOX_TX_QUEUE_LEN) which needs to removed to even get the
remote chance of hit the corner case.
Note, this delay doesn't just have to be at the SCPI end. We could get
preempted here (?) before actually sending the command to the SCP and
other kernel threads or processes could send those other 256 commands
before we get to run again.
Agreed, but we would still timeout after 3 jiffies max.
Wouldn't it be better instead to have scpi_alloc_xfer_list add a unique
number to each struct scpi_xfer.
One of reason using it part of command is that SCP gives it back in the
response to compare.
+
+ msg->slot = BIT(SCPI_SLOT);
+ msg->cmd = PACK_SCPI_CMD(cmd, token, len);
+ msg->tx_buf = tx_buf;
+ msg->tx_len = len;
+ msg->rx_buf = rx_buf;
+ init_completion(&msg->done);
+
+ ret = mbox_send_message(scpi_chan->chan, msg);
+ if (ret < 0 || !rx_buf)
+ goto out;
+
+ if (!wait_for_completion_timeout(&msg->done, MAX_RX_TIMEOUT))
+ ret = -ETIMEDOUT;
+ else
+ /* first status word */
+ ret = le32_to_cpu(msg->status);
+out:
+ if (ret < 0 && rx_buf) /* remove entry from the list if timed-out */
So, even with my suggestion that the unique message identifies are
fixed values stored in struct scpi_xfer, we can still have the situation
where we timeout a request, that scpi_xfer then getting used for another
request, and finally the SCP completes the request that we timed out,
which has the same 'unique' value as the later one.
As explained above I can't imagine hitting this condition. I will think
more on that again.
One way to handle that it to not have any timeout on requests and assume
the firmware isn't buggy.
That's something I can't do ;) based on my experience so far. It's good
to assume firmware *can be buggy* and handle all possible errors. Think
about the development firmware using this driver. This has been very
useful when I was testing the development versions. Even under stress
conditions I still see timeouts(very rarely though), so my personal
preference is to have them.
Another way is to have something more closely approximating unique in
the message, e.g. a 64-bit incrementing count. I realise though that
ARM have already finished the spec so we're limited to 8-bits :-(
+ scpi_process_cmd(scpi_chan, msg->cmd);
+
+ put_scpi_xfer(msg, scpi_chan);
+ /* SCPI error codes > 0, translate them to Linux scale*/
+ return ret > 0 ? scpi_to_linux_errno(ret) : ret;
+}
+
+static u32 scpi_get_version(void)
+{
+ return scpi_info->protocol_version;
+}
+
+static int
+scpi_clk_get_range(u16 clk_id, unsigned long *min, unsigned long *max)
+{
+ int ret;
+ struct clk_get_info clk;
+ __le16 le_clk_id = cpu_to_le16(clk_id);
+
+ ret = scpi_send_message(SCPI_CMD_GET_CLOCK_INFO,
+ &le_clk_id, sizeof(le_clk_id), &clk);
+ if (!ret) {
+ *min = le32_to_cpu(clk.min_rate);
+ *max = le32_to_cpu(clk.max_rate);
+ }
+ return ret;
+}
+
+static unsigned long scpi_clk_get_val(u16 clk_id)
+{
+ int ret;
+ struct clk_get_value clk;
+ __le16 le_clk_id = cpu_to_le16(clk_id);
+
+ ret = scpi_send_message(SCPI_CMD_GET_CLOCK_VALUE,
+ &le_clk_id, sizeof(le_clk_id), &clk);
+ return ret ? ret : le32_to_cpu(clk.rate);
+}
+
+static int scpi_clk_set_val(u16 clk_id, unsigned long rate)
+{
+ int stat;
+ struct clk_set_value clk = {
+ cpu_to_le16(clk_id), 0, cpu_to_le32(rate)
I know that '0' is what I suggested when I spotted the 'reserved' member
wasn't being allowed for, but I have since thought that the more robust
way of initialising structures here, and in other functions below,
might be with this syntax:
.id = cpu_to_le16(clk_id),
.rate = cpu_to_le32(rate)
Ok will update.
[...]
+static int scpi_probe(struct platform_device *pdev)
+{
+ int count, idx, ret;
+ struct resource res;
+ struct scpi_chan *scpi_chan;
+ struct device *dev = &pdev->dev;
+ struct device_node *np = dev->of_node;
+
+ scpi_info = devm_kzalloc(dev, sizeof(*scpi_info), GFP_KERNEL);
+ if (!scpi_info) {
+ dev_err(dev, "failed to allocate memory for scpi drvinfo\n");
+ return -ENOMEM;
+ }
+
+ count = of_count_phandle_with_args(np, "mboxes", "#mbox-cells");
+ if (count < 0) {
+ dev_err(dev, "no mboxes property in '%s'\n", np->full_name);
+ return -ENODEV;
+ }
+
+ scpi_chan = devm_kcalloc(dev, count, sizeof(*scpi_chan), GFP_KERNEL);
+ if (!scpi_chan) {
+ dev_err(dev, "failed to allocate memory scpi chaninfo\n");
+ return -ENOMEM;
+ }
+
+ for (idx = 0; idx < count; idx++) {
+ resource_size_t size;
+ struct scpi_chan *pchan = scpi_chan + idx;
+ struct mbox_client *cl = &pchan->cl;
+ struct device_node *shmem = of_parse_phandle(np, "shmem", idx);
+
+ if (of_address_to_resource(shmem, 0, &res)) {
+ dev_err(dev, "failed to get SCPI payload mem resource\n");
+ ret = -EINVAL;
+ goto err;
+ }
+
+ size = resource_size(&res);
+ pchan->rx_payload = devm_ioremap(dev, res.start, size);
+ if (!pchan->rx_payload) {
+ dev_err(dev, "failed to ioremap SCPI payload\n");
+ ret = -EADDRNOTAVAIL;
+ goto err;
+ }
+ pchan->tx_payload = pchan->rx_payload + (size >> 1);
+
+ cl->dev = dev;
+ cl->rx_callback = scpi_handle_remote_msg;
+ cl->tx_prepare = scpi_tx_prepare;
+ cl->tx_block = true;
+ cl->tx_tout = 50;
+ cl->knows_txdone = false; /* controller can ack */
+
+ INIT_LIST_HEAD(&pchan->rx_pending);
+ INIT_LIST_HEAD(&pchan->xfers_list);
+ spin_lock_init(&pchan->rx_lock);
+ mutex_init(&pchan->xfers_lock);
+
+ ret = scpi_alloc_xfer_list(dev, pchan);
+ if (!ret) {
+ pchan->chan = mbox_request_channel(cl, idx);
+ if (!IS_ERR(pchan->chan))
+ continue;
+ ret = -EPROBE_DEFER;
+ dev_err(dev, "failed to acquire channel#%d\n", idx);
+ }
+err:
+ scpi_free_channels(dev, scpi_chan, idx);
Think we need to add one to 'idx' above, otherwise we won't free up
resources we successfully allocated to the current channel before we got
the error.
Actually, we also fail to free scpi_chan and scpi_info, so should we not
just call scpi_remove here instead? (Would require some tweaks as
scpi_info and drvdata aren't set until a bit further down.)
Ok need to look at this again. Few thinks I left assuming devm_* will
handle it. I will also try to check if there's any memleaks.
Regards,
Sudeep
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