linux-kernel - Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple connections

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Message-ID: <37b3749e-2363-0877-c318-9c334a5d1881@arm.com>
Date:   Mon, 11 May 2020 15:30:46 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     saiprakash.ranjan@...eaurora.org, mike.leach@...aro.org
Cc:     mathieu.poirier@...aro.org, swboyd@...omium.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux@...linux.org.uk
Subject: Re: [PATCH] coresight: dynamic-replicator: Fix handling of multiple
 connections

On 05/11/2020 03:16 PM, Sai Prakash Ranjan wrote:
> Hi Mike,
> 
> On 2020-05-11 16:44, Mike Leach wrote:
> [...]
> 
>>>
>>> I checked with the debug team and there is a limitation with
>>> the replicator(swao_replicator) in the AOSS group where it
>>> loses the idfilter register context when the clock is disabled.
>>> This is not just in SC7180 SoC but also reported on some latest
>>> upcoming QCOM SoCs as well and will need to be taken care in
>>> order to enable coresight on these chipsets.
>>>
>>> Here's what's happening -  After the replicator is initialized,
>>> the clock is disabled in amba_pm_runtime_suspend() as a part of
>>> pm runtime workqueue with the assumption that there will be no
>>> loss of context after the replicator is initialized. But it doesn't
>>> hold good with the replicators with these unfortunate limitation
>>> and the idfilter register context is lost.
>>>
>>> [    5.889406] amba_pm_runtime_suspend devname=6b06000.replicator ret=0
>>> [    5.914516] Workqueue: pm pm_runtime_work
>>> [    5.918648] Call trace:
>>> [    5.921185]  dump_backtrace+0x0/0x1d0
>>> [    5.924958]  show_stack+0x2c/0x38
>>> [    5.928382]  dump_stack+0xc0/0x104
>>> [    5.931896]  amba_pm_runtime_suspend+0xd8/0xe0
>>> [    5.936469]  __rpm_callback+0xe0/0x140
>>> [    5.940332]  rpm_callback+0x38/0x98
>>> [    5.943926]  rpm_suspend+0xec/0x618
>>> [    5.947522]  rpm_idle+0x5c/0x3f8
>>> [    5.950851]  pm_runtime_work+0xa8/0xc0
>>> [    5.954718]  process_one_work+0x1f8/0x4c0
>>> [    5.958848]  worker_thread+0x50/0x468
>>> [    5.962623]  kthread+0x12c/0x158
>>> [    5.965957]  ret_from_fork+0x10/0x1c
>>>
>>> This is a platform/SoC specific replicator issue, so we can either
>>> introduce some DT property for replicators to identify which replicator
>>> has this limitation, check in replicator_enable() and reset the
>>> registers
>>> or have something like below diff to check the idfilter registers in
>>> replicator_enable() and then reset with clear comment specifying it’s
>>> the
>>> hardware limitation on some QCOM SoCs. Please let me know your thoughts
>>> on
>>> this?
>>>
> 
> Sorry for hurrying up and sending the patch - 
> https://lore.kernel.org/patchwork/patch/1239923/.
> I will send v2 based on further feedbacks here or there.
> 
>>
>> 1) does this replicator part have a unique ID that differs from the
>> standard ARM designed replicators?
>> If so perhaps link the modification into this. (even if the part no in
>> PIDR0/1 is the same the UCI should be different for a different
>> implementation)
>>
> 
> pid=0x2bb909 for both replicators. So part number is same.
> UCI will be different for different implementation(QCOM maybe different 
> from ARM),
> but will it be different for different replicators under the same 
> impl(i.e., on QCOM).

May be use PIDR4.DES_2 to match the Implementor and apply the work
around for all QCOM replicators ?

To me that sounds the best option.

Suzuki