linux-kernel - Re: [PATCH V2] coresight: tmc: Make etr buffer mode user configurable from sysfs

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Message-ID: <ffa90e80-c249-42d5-26f1-dc022d91e5a9@os.amperecomputing.com>
Date:   Wed, 23 Aug 2023 16:10:02 -0700
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
Subject: Re: [PATCH V2] coresight: tmc: Make etr buffer mode user configurable
 from sysfs


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
>>
>>