linux-kernel - Re: [PATCH v2 5/5] hwtracing: hisi_ptt: Add dummy callback pmu::read()

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Date:   Fri, 15 Sep 2023 13:53:56 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Yicong Yang <yangyicong@...wei.com>, mathieu.poirier@...aro.org,
        jonathan.cameron@...wei.com, linux-kernel@...r.kernel.org
Cc:     alexander.shishkin@...ux.intel.com, helgaas@...nel.org,
        linux-pci@...r.kernel.org, prime.zeng@...ilicon.com,
        linuxarm@...wei.com, yangyicong@...ilicon.com, hejunhao3@...wei.com
Subject: Re: [PATCH v2 5/5] hwtracing: hisi_ptt: Add dummy callback
 pmu::read()

On 14/09/2023 12:22, Yicong Yang wrote:
> From: Junhao He <hejunhao3@...wei.com>
> 
> When start trace with perf option "-C $cpu" and immediately stop it
> with SIGTERM or others, the perf core will invoke pmu::read() while
> the driver doesn't implement it. Add a dummy pmu::read() to avoid
> any issues.

What issues are we talking about here ? Shouldn't the core perf
skip the call, if pmu::read() is not available ?

Suzuki

> 
> Signed-off-by: Junhao He <hejunhao3@...wei.com>
> Signed-off-by: Yicong Yang <yangyicong@...ilicon.com>
> Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
>   drivers/hwtracing/ptt/hisi_ptt.c | 5 +++++
>   1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/hwtracing/ptt/hisi_ptt.c b/drivers/hwtracing/ptt/hisi_ptt.c
> index 62a444f5228e..c1b5fd2b8974 100644
> --- a/drivers/hwtracing/ptt/hisi_ptt.c
> +++ b/drivers/hwtracing/ptt/hisi_ptt.c
> @@ -1184,6 +1184,10 @@ static void hisi_ptt_pmu_del(struct perf_event *event, int flags)
>   	hisi_ptt_pmu_stop(event, PERF_EF_UPDATE);
>   }
>   
> +static void hisi_ptt_pmu_read(struct perf_event *event)
> +{
> +}
> +
>   static void hisi_ptt_remove_cpuhp_instance(void *hotplug_node)
>   {
>   	cpuhp_state_remove_instance_nocalls(hisi_ptt_pmu_online, hotplug_node);
> @@ -1227,6 +1231,7 @@ static int hisi_ptt_register_pmu(struct hisi_ptt *hisi_ptt)
>   		.stop		= hisi_ptt_pmu_stop,
>   		.add		= hisi_ptt_pmu_add,
>   		.del		= hisi_ptt_pmu_del,
> +		.read		= hisi_ptt_pmu_read,
>   	};
>   
>   	reg = readl(hisi_ptt->iobase + HISI_PTT_LOCATION);