linux-kernel - Re: [PATCH V3 3/4] coresight: trbe: Add a representative coresight_platform

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Message-ID: <ee50cd93-b561-9a26-c7c4-90cb1f6a2192@arm.com>
Date:   Fri, 4 Aug 2023 11:04:25 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Sami Mujawar <sami.mujawar@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Mike Leach <mike.leach@...aro.org>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        James Clark <james.clark@....com>, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V3 3/4] coresight: trbe: Add a representative
 coresight_platform_data for TRBE

On 04/08/2023 10:18, Anshuman Khandual wrote:
> 
> 
> On 8/3/23 19:25, Suzuki K Poulose wrote:
>> On 03/08/2023 06:56, Anshuman Khandual wrote:
>>> TRBE coresight devices do not need regular connections information, as the
>>> paths get built between all percpu source and their respective percpu sink
>>> devices. Please refer 'commit 2cd87a7b293d ("coresight: core: Add support
>>> for dedicated percpu sinks")' which added support for percpu sink devices.
>>>
>>> coresight_register() expect device connections via the platform_data. TRBE
>>> devices do not have any graph connections and thus is empty. With upcoming
>>> ACPI support for TRBE, we do not get a real acpi_device and thus
>>> coresight_get_platform_dat() will end up in failures. Hence this allocates
>>> a zeroed coresight_platform_data structure and assigns that back into the
>>> device.
>>>
>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>> Cc: Mike Leach <mike.leach@...aro.org>
>>> Cc: Leo Yan <leo.yan@...aro.org>
>>> Cc: Alexander Shishkin <alexander.shishkin@...ux.intel.com>
>>> Cc: coresight@...ts.linaro.org
>>> Cc: linux-arm-kernel@...ts.infradead.org
>>> Cc: linux-kernel@...r.kernel.org
>>> Signed-off-by: Anshuman Khandual <anshuman.khandual@....com>
>>> ---
>>>    drivers/hwtracing/coresight/coresight-trbe.c | 6 +++---
>>>    1 file changed, 3 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/drivers/hwtracing/coresight/coresight-trbe.c b/drivers/hwtracing/coresight/coresight-trbe.c
>>> index 7720619909d6..e1d9d06e7725 100644
>>> --- a/drivers/hwtracing/coresight/coresight-trbe.c
>>> +++ b/drivers/hwtracing/coresight/coresight-trbe.c
>>> @@ -1494,9 +1494,9 @@ static int arm_trbe_device_probe(struct platform_device *pdev)
>>>        if (!drvdata)
>>>            return -ENOMEM;
>>>    -    pdata = coresight_get_platform_data(dev);
>>> -    if (IS_ERR(pdata))
>>> -        return PTR_ERR(pdata);
>>> +    pdata = devm_kzalloc(dev, sizeof(*pdata), GFP_KERNEL);
>>> +    if (!pdata)
>>> +        return -ENOMEM;
>>
>> Please could you add a comment in here, on why we use a dummy platform
>> data ? It is good to have documented it in the code too.
> 
> Sure, will add the following in-code documentation.
> 
> +       /*
> +        * TRBE coresight devices do not need regular connections
> +        * information, as the paths get built between all percpu
> +        * source and their respective percpu sink devices. Though
> +        * coresight_register() expect device connections via the
> +        * platform_data, which TRBE devices do not have. As they
> +        * are not real ACPI devices, coresight_get_platform_dat()

minor nit: s/coresight_get_platform_dat/coresight_get_platform_data/
here and above in the description.

Otherwise, looks good.

Suzuki