linux-kernel - Re: [PATCH] stm: class: Add MIPI OST protocol support

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Message-ID: <37ec6af5-f71b-7a92-9c59-1c89595382bc@quicinc.com>
Date:   Tue, 7 Mar 2023 21:26:19 +0800
From:   Jinlong Mao <quic_jinlmao@...cinc.com>
To:     Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Maxime Coquelin <mcoquelin.stm32@...il.com>,
        Alexandre Torgue <alexandre.torgue@...s.st.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Tingwei Zhang <quic_tingweiz@...cinc.com>,
        Yuanfang Zhang <quic_yuanfang@...cinc.com>,
        "Tao Zhang" <quic_taozha@...cinc.com>,
        Hao Zhang <quic_hazha@...cinc.com>
Subject: Re: [PATCH] stm: class: Add MIPI OST protocol support

Hi Alexande,

On 3/3/2023 2:05 AM, Alexander Shishkin wrote:
> Mao Jinlong <quic_jinlmao@...cinc.com> 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