linux-kernel - Re: [PATCH 1/2] coresight: Set affinity to invalid for missing CPU phandle

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Message-ID: <fc72dab8-d287-38d4-1abd-faca02c09118@codeaurora.org>
Date:   Thu, 20 Jun 2019 20:24:21 +0530
From:   Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        mathieu.poirier@...aro.org, leo.yan@...aro.org,
        alexander.shishkin@...ux.intel.com, andy.gross@...aro.org,
        david.brown@...aro.org, mark.rutland@....com
Cc:     rnayak@...eaurora.org, vivek.gautam@...eaurora.org,
        sibis@...eaurora.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH 1/2] coresight: Set affinity to invalid for missing CPU
 phandle

Hi Suzuki,

Thanks for the review.

On 6/20/2019 7:25 PM, Suzuki K Poulose wrote:
> 
> Sai,
> 
> Thanks for the patch. Please could you change the subject to :
> 
> "coresight: Do not default to CPU0 for missing CPU phandle"
> 

Sure.

> On 20/06/2019 14:45, Sai Prakash Ranjan wrote:
>> Affinity defaults to CPU0 in case of missing CPU phandle
>> and this leads to crashes in some cases because of such
>> wrong assumption. Fix this by returning -ENODEV in
> 
> Thats not the right justification. Causing crashes is due to
> bad DT/firmware. I would be happy with something like :
> 
> "Coresight platform support assumes that a missing \"cpu\" phandle
> defaults to CPU0. This could be problematic and unnecessarily binds
> components to CPU0, where they may not be. Let us make the DT binding
> rules a bit stricter by not defaulting to CPU0 for missing "cpu"
> affinity information."
> 
> Also, you must
> 
> 1) update the devicetree/bindings document to reflect the same.
> 2) update the drivers to take appropriate action on the missing CPU
>     where they are expected (e.g, CPU-debug, etm*), to prevent
>     breaking a bisect.
> 
> 

Sure will do it and repost.

>> coresight platform for such cases and then handle it
>> in the coresight drivers.
>>
>> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
>> ---
>>   drivers/hwtracing/coresight/coresight-platform.c | 10 ++++++----
>>   1 file changed, 6 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/hwtracing/coresight/coresight-platform.c 
>> b/drivers/hwtracing/coresight/coresight-platform.c
>> index 3c5ceda8db24..b1ea60c210e1 100644
>> --- a/drivers/hwtracing/coresight/coresight-platform.c
>> +++ b/drivers/hwtracing/coresight/coresight-platform.c
>> @@ -160,15 +160,17 @@ static int of_coresight_get_cpu(struct device *dev)
>>       if (!dev->of_node)
>>           return 0;
>> +
>>       dn = of_parse_phandle(dev->of_node, "cpu", 0);
>> -    /* Affinity defaults to CPU0 */
>> +
>> +    /* Affinity defaults to invalid if no cpu nodes are found*/
> 
> The code is self explanatory here. You could drop the comment.
> 

Sure.

>>       if (!dn)
>> -        return 0;
>> +        return -ENODEV;
>> +
>>       cpu = of_cpu_node_to_id(dn);
>>       of_node_put(dn);
>> -    /* Affinity to CPU0 if no cpu nodes are found */
>> -    return (cpu < 0) ? 0 : cpu;
>> +    return cpu;
>>   }
> 
> Suzuki

-Sai

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