Message-ID: <25f46f87-2090-46ca-9ef7-1310b4360801@os.amperecomputing.com>
Date:   Mon, 4 Dec 2023 13:41:32 -0800
From:   Steve Clevenger <scclevenger@...amperecomputing.com>
To:     Suzuki K Poulose <suzuki.poulose@....com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Mike Leach <mike.leach@...aro.org>,
        James Clark <james.clark@....com>,
        Leo Yan <leo.yan@...aro.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        coresight@...ts.linaro.org, linux-kernel@...r.kernel.org,
        Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH V2] coresight: tmc: Make etr buffer mode user configurable
 from sysfs


Hi Suzuki,

On 9/7/2023 2:31 PM, Steve Clevenger wrote:
> 
> Hi Suzuki,
> 
> On 9/1/2023 5:22 AM, Suzuki K Poulose wrote:
>> Hi Steve
>>
>> On 30/08/2023 17:04, Suzuki K Poulose wrote:
>>> Cc: Sudeep
>>>
>>> Hi Steve
>>>
>>> On 28/08/2023 17:35, Steve Clevenger wrote:
>>>>
>>>> Hi Suzuki,
>>>>
>>>> On 8/27/2023 2:35 PM, Suzuki K Poulose wrote:
>>>>> Hi Steve
>>>>>
>>>>> On 26/08/2023 01:14, Steve Clevenger wrote:
>>>>>>
>>>>>> Unfortunately, I tested with the original patch not [PATCH V2]. I've
>>>>>> remedied this. My results below:
>>>>>>
>>>>>> [root@...01sys-b212 linux]# cat
>>>>>> /sys/devices/system/cpu/cpu123/ARMHC501\:23/tmc_etr35/buf_modes_available
>>>>>> auto flat catu
>>>>>> [root@...01sys-b212 linux]# cat
>>>>>> /sys/devices/system/cpu/cpu123/ARMHC501\:23/tmc_etr35/buf_mode_preferred
>>>>>> auto
>>>>>> [root@...01sys-b212 linux]# echo "catu" >
>>>>>> /sys/devices/system/cpu/cpu123/ARMHC501\:23/tmc_etr35/buf_mode_preferred
>>>>>> [root@...01sys-b212 linux]# cat
>>>>>> /sys/devices/system/cpu/cpu123/ARMHC501\:23/tmc_etr35/buf_mode_preferred
>>>>>> catu
>>>>>>
>>>>>> As with the V1 patch, auto defaults to catu.
>>>>>>
>>>>>> I expected to see tmc-sg (former default) as an available mode, but do
>>>>>> not. As I recall, the buffer mode defaulted to ETR scatter-gather
>>>>>> prior
>>>>>> to this patch. Must this capability now be explicitly advertised? I've
>>>>>> seen this done as "arm,scatter-gather" in device trees, but not
>>>>>> used by
>>>>>> Ampere. Perhaps someone can enlighten me.
>>>>>
>>>>> Yes, you must add that property to the TMC-ETR node (for both DT and
>>>>> ACPI). In the past, almost all of the TMC-ETRs (except Juno board)
>>>>> locked up the system while using the SG mode (due to the interconnect
>>>>> issues, something to do with the transaction). Thus, we decided to
>>>>> add a property explicitly enabling this for a given platform.
>>>>>
>>>>> When you mentioned, it was using TMC-ETR SG mode, how did you verify
>>>>> this ? Please be aware that the table allocation code etc are shared
>>>>> by both TMC-SG and CATU.
>>>>>
>>>>
>>>> You might recall how this started. I had no way to test the CATU due to
>>>> the order the ETR modes defaulted (Flat, ETR-SG, CATU). For test
>>>> purposes, I programmatically swapped the ETR-SG/CATU order and could
>>>> then verify CATU operation by the driver calling into CATU code. This
>>>
>>> So, were you using the DT based boot for the above runs ?
>>>
>>>> suggests Flat mode was bypassed, and the driver defaulted to ETR-SG
>>>> prior to this hack. This didn't offer the user any control, hence my
>>>> feature request. Note that most of the early Ampere self-hosted trace
>>>> collection used ETR-SG. Now I can't select it.
>>>
>>>
>>>>
>>>> How is this property described in the ACPI? The "ACPI for CoreSight™ 1.1
>>>> Platform Design Document" (DEN0067) doesn't describe this.
>>>
>>> This is not specified in the ACPI platform design document. I can get
>>> it fixed. Ideally we need a property describing that the scatter-gather
>>> mode is safe to use.
>>
>> Looks like this is not straight forward copying of DT property. We are
>> investigating this on our side and will get back to you.

I noticed this work is queued for 6.7 (coresight-next-6.7). Do you have
an update to the ACPI platform design document Ampere can use to base an
update so the scatter-gather mode can be used?

Thanks,
Steve

>>
> 
> The intent behind my request was to have a way to SysFS configure the
> (available) ETR mode. Unless there's a change to the ACPI, the CATU is
> the only SG option for Ampere in the near term.
> 
> Thanks,
> Steve
> 
> 
>> Suzuki
>>
>>
>>>
>>> DT uses "arm,scatter-gather" property [0] and this is what we now expect
>>> in the ACPI based systems too.
>>>
>>> https://elixir.bootlin.com/linux/latest/source/Documentation/devicetree/bindings/arm/arm,coresight-tmc.yaml#:~:text=71-,72,-73
>>>
>>> Does it sound fine ?
>>>
>>> Suzuki
>>>
>>>>
>>>> Thanks,
>>>> Steve
>>>>
>>>>
>>>>> Kind regards
>>>>> Suzuki
>>>>>
>>>>>>
>>>>>> Steve C.
>>>>>>
>>>>>> On 8/23/2023 4:10 PM, Steve Clevenger wrote:
>>>>>>>
>>>>>>> Here's some quick feedback. My system shows two modes available; auto
>>>>>>> catu
>>>>>>>
>>>>>>> etr_buf_mode_current is writable. I expected to see tmc-sg (former
>>>>>>> default) listed in etr_buf_modes_available but it doesn't show up.
>>>>>>>
>>>>>>> Note that both the auto and catu etr_buf_mode_current settings
>>>>>>> default
>>>>>>> to catu. My understanding is auto should revert to the default
>>>>>>> behavior.
>>>>>>> On my system the default was tmc-sg.
>>>>>>>
>>>>>>> More later.
>>>>>>>
>>>>>>> [root@...01sys-b212 kernel]# cat
>>>>>>> /sys/devices/system/cpu/cpu20/ARMHC501\:60/tmc_etr96/etr_buf_modes_available
>>>>>>>
>>>>>>> auto catu
>>>>>>> [root@...01sys-b212 kernel]# cat
>>>>>>> /sys/devices/system/cpu/cpu20/ARMHC501\:60/tmc_etr96/etr_buf_mode_current
>>>>>>> catu
>>>>>>> [root@...01sys-b212 kernel]# echo "catu" >
>>>>>>> /sys/devices/system/cpu/cpu20/ARMHC501\:60/tmc_etr96/etr_buf_mode_current
>>>>>>> [root@...01sys-b212 kernel]# cat
>>>>>>> /sys/devices/system/cpu/cpu20/ARMHC501\:60/tmc_etr96/etr_buf_mode_current
>>>>>>> catu
>>>>>>>
>>>>>>> Steve C.
>>>>>>>
>>>>>>>
>>>>>>> On 8/21/2023 12:40 PM, Steve Clevenger wrote:
>>>>>>>>
>>>>>>>> Hi Suzuki,
>>>>>>>>
>>>>>>>> I may be able to test it this week. You've already pointed me at the
>>>>>>>> patch thread(s). The main holdup is I need to merge the 6.6 pending
>>>>>>>> platform work in order to use the Ampere ACPI. I couldn't get these
>>>>>>>> patches to apply directly to 6.4 last I tried.
>>>>>>>>
>>>>>>>> Steve C.
>>>>>>>>
>>>>>>>> On 8/18/2023 2:39 AM, Suzuki K Poulose wrote:
>>>>>>>>> Cc: Steve
>>>>>>>>>
>>>>>>>>> Steve,
>>>>>>>>>
>>>>>>>>> Are you able to test this with CATU ?
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 18/08/2023 09:21, Anshuman Khandual wrote:
>>>>>>>>>> Currently TMC-ETR automatically selects the buffer mode from all
>>>>>>>>>> available
>>>>>>>>>> methods in the following sequentially fallback manner - also in
>>>>>>>>>> that
>>>>>>>>>> order.
>>>>>>>>>>
>>>>>>>>>> 1. FLAT mode with or without IOMMU
>>>>>>>>>> 2. TMC-ETR-SG (scatter gather) mode when available
>>>>>>>>>> 3. CATU mode when available
>>>>>>>>>>
>>>>>>>>>> But this order might not be ideal for all situations. For
>>>>>>>>>> example if
>>>>>>>>>> there
>>>>>>>>>> is a CATU connected to ETR, it may be better to use TMC-ETR
>>>>>>>>>> scatter
>>>>>>>>>> gather
>>>>>>>>>> method, rather than CATU. But hard coding such order changes will
>>>>>>>>>> prevent
>>>>>>>>>> us from testing or using a particular mode. This change provides
>>>>>>>>>> following
>>>>>>>>>> new sysfs tunables for the user to control TMC-ETR buffer mode
>>>>>>>>>> explicitly,
>>>>>>>>>> if required. This adds following new sysfs files for buffer mode
>>>>>>>>>> selection
>>>>>>>>>> purpose explicitly in the user space.
>>>>>>>>>>
>>>>>>>>>> /sys/bus/coresight/devices/tmc_etr<N>/buf_modes_available
>>>>>>>>>> /sys/bus/coresight/devices/tmc_etr<N>/buf_mode_preferred
>>>>>>>>>>
>>>>>>>>>> $ cat buf_modes_available
>>>>>>>>>> auto flat tmc-sg catu    ------------------> Supported TMC-ETR
>>>>>>>>>> buffer
>>>>>>>>>> modes
>>>>>>>>>>
>>>>>>>>>> $ echo catu > buf_mode_preferred   -------> Explicit buffer mode
>>>>>>>>>> request
>>>>>>>>>>
>>>>>>>>>> But explicit user request has to be within supported ETR buffer
>>>>>>>>>> modes
>>>>>>>>>> only.
>>>>>>>>>> These sysfs interface files are exclussive to ETR, and hence these
>>>>>>>>>> are
>>>>>>>>>> not
>>>>>>>>>> available for other TMC devices such as ETB or ETF etc.
>>>>>>>>>>
>>>>>>>>>> A new auto' mode (i.e ETR_MODE_AUTO) has been added to help
>>>>>>>>>> fallback
>>>>>>>>>> to the
>>>>>>>>>> existing default behaviour, when user provided preferred buffer
>>>>>>>>>> mode
>>>>>>>>>> fails.
>>>>>>>>>> ETR_MODE_FLAT and ETR_MODE_AUTO are always available as preferred
>>>>>>>>>> modes.
>>>>>>>>>>
>>>>>>>>>> Cc: Suzuki K Poulose <suzuki.poulose@....com>
>>>>>>>>>> Cc: Mike Leach <mike.leach@...aro.org>
>>>>>>>>>> Cc: James Clark <james.clark@....com>
>>>>>>>>>> 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>
>>>>>>>>>> ---
>>>>>>>>>> This applies on v6.5-rc6
>>>>>>>>>>
>>>>>>>>>> Changes in V2:
>>>>>>>>>>
>>>>>>>>>> - Renamed sysfs file etr_buf_modes_available as
>>>>>>>>>> buf_modes_available
>>>>>>>>>> - Renamed sysfs file buf_mode_current as buf_mode_preferred
>>>>>>>>>> - Renamed etr_supports_flat_mode() as etr_can_use_flat_mode()
>>>>>>>>>> - Renamed coresight_tmc_groups[] as coresight_etf_groups[]
>>>>>>>>>> - Reused coresight_tmc_group[] for trigger_cntr and buffer_size
>>>>>>>>>> - Fallback trying ETR_MODE_AUTO when user preferred mode fails
>>>>>>>>>> - Moved ETR sysfs details into coresight-tmc-etr.c
>>>>>>>>>> - Dropped etr_can_use_flat_mode() check while offering
>>>>>>>>>> ETR_MODE_FLAT
>>>>>>>>>> in sysfs
>>>>>>>>>> - Moved struct etr_buf_hw inside coresight-tmc-etr.c
>>>>>>>>>> - Moved get_etr_buf_hw() and etr_can_use_flat_mode() inside
>>>>>>>>>> coresight-tmc-etr.c
>>>>>>>>>> - Updated month in
>>>>>>>>>> Documentation/ABI/testing/sysfs-bus-coresight-devices-tmc
>>>>>>>>>>
>>>>>>>>>> Changes in V1:
>>>>>>>>>>
>>>>>>>>>> https://lore.kernel.org/all/20230728084837.276551-1-anshuman.khandual@arm.com/
>>>>>>>>>>
>>>>>>>>>>     .../testing/sysfs-bus-coresight-devices-tmc   |  16 +++
>>>>>>>>>>     .../hwtracing/coresight/coresight-tmc-core.c  |  15 ++-
>>>>>>>>>>     .../hwtracing/coresight/coresight-tmc-etr.c   | 111
>>>>>>>>>> ++++++++++++++++--
>>>>>>>>>>     drivers/hwtracing/coresight/coresight-tmc.h   |   3 +
>>>>>>>>>>     4 files changed, 131 insertions(+), 14 deletions(-)
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> Looks good to me.
>>>>>>>>>
>>>>>>>>> Suzuki
>>>>>>>>>
>>>>>>>>>
>>>>>
>>>
>>

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