Message-ID: <1b2a035c-489e-ace9-f851-c1ec157ff9fa@arm.com>
Date:   Sun, 27 Aug 2023 22:35:16 +0100
From:   Suzuki K Poulose <suzuki.poulose@....com>
To:     scclevenger@...amperecomputing.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

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.

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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