Hi Alexande,
On 3/3/2023 2:05 AM, Alexander Shishkin wrote:
Mao Jinlong <quic_jinlmao@xxxxxxxxxxx> writes:
Add MIPI OST protocol support for stm to format the traces.
Missing an explanation of what OST is, what it's used for, how it is
different from the SyS-T and others.
I will updae the explanation in next version.
Framework copied from drivers/hwtracing/stm.p-sys-t.c as of
You mean stm/p_sys-t.c. Also, it's not a framework, it's a driver.
The driver refers to code structure of p_sys-t driver. So, add this
comments after
internal review.
commit d69d5e83110f ("stm class: Add MIPI SyS-T protocol
support").
Why is this significant?
diff --git a/drivers/hwtracing/stm/p_ost.c b/drivers/hwtracing/stm/p_ost.c
new file mode 100644
index 000000000000..2ca1a3fda57f
--- /dev/null
+++ b/drivers/hwtracing/stm/p_ost.c
@@ -0,0 +1,95 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copied from drivers/hwtracing/stm.p-sys-t.c as of commit d69d5e83110f
+ * ("stm class: Add MIPI SyS-T protocol support").
Same as in the commit message.
[...]
+#define OST_TOKEN_STARTSIMPLE (0x10)
+#define OST_VERSION_MIPI1 (0x10 << 8)
+#define OST_ENTITY_FTRACE (0x01 << 16)
+#define OST_CONTROL_PROTOCOL (0x0 << 24)
These could use an explanation.
I will add the explanation.
+#define DATA_HEADER (OST_TOKEN_STARTSIMPLE | OST_VERSION_MIPI1 | \
+ OST_ENTITY_FTRACE | OST_CONTROL_PROTOCOL)
Does this mean that everything is ftrace? Because it's not.
Only ftrace is supported in p_ost now. Other header type will be added
later.
+
+#define STM_MAKE_VERSION(ma, mi) ((ma << 8) | mi)
+#define STM_HEADER_MAGIC (0x5953)
+
+static ssize_t notrace ost_write(struct stm_data *data,
+ struct stm_output *output, unsigned int chan,
+ const char *buf, size_t count)
+{
+ unsigned int c = output->channel + chan;
+ unsigned int m = output->master;
+ const unsigned char nil = 0;
+ u32 header = DATA_HEADER;
+ u8 trc_hdr[24];
+ ssize_t sz;
+
+ /*
+ * STP framing rules for OST frames:
+ * * the first packet of the OST frame is marked;
+ * * the last packet is a FLAG.
Which in your case is also timestamped.
I will add the comments.
+ */
+ /* Message layout: HEADER / DATA / TAIL */
+ /* HEADER */
+
+ sz = data->packet(data, m, c, STP_PACKET_DATA, STP_PACKET_MARKED,
+ 4, (u8 *)&header);
The /* HEADER */ comment applies to the above line, so it should
probably be directly before it.
Got it.
+ if (sz <= 0)
+ return sz;
+ *(uint16_t *)(trc_hdr) = STM_MAKE_VERSION(0, 3);
+ *(uint16_t *)(trc_hdr + 2) = STM_HEADER_MAGIC;
+ *(uint32_t *)(trc_hdr + 4) = raw_smp_processor_id();
+ *(uint64_t *)(trc_hdr + 8) = sched_clock();
Why sched_clock()? It should, among other things, be called with
interrupts disabled, which is not the case here.
I will check. If it is not necessary here, I will remove it.
+ *(uint64_t *)(trc_hdr + 16) = task_tgid_nr(get_current());
Is there a reason why trc_hdr is not a struct?
No particular reason here.
Thanks,
--
Alex
