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.
> 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.
> 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.
> +#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.
> +
> +#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.
> + */
> + /* 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.
> + 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.
> + *(uint64_t *)(trc_hdr + 16) = task_tgid_nr(get_current());
Is there a reason why trc_hdr is not a struct?
Thanks,
--
Alex
