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

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Message-ID: <391951c3-7da9-3965-acf8-f3b31f822879@os.amperecomputing.com>
Date:   Fri, 25 Aug 2023 17:14:42 -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


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.

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
>>>
>>>