linux-kernel - Re: [PATCH v4 00/30] coresight: Support for ACPI bindings

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Message-ID: <20190528051924.GA19112@leoy-ThinkPad-X240s>
Date:   Tue, 28 May 2019 13:19:24 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Suzuki K Poulose <suzuki.poulose@....com>
Cc:     linux-arm-kernel@...ts.infradead.org, coresight@...ts.linaro.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 00/30] coresight: Support for ACPI bindings

Hi Suzuki,

On Wed, May 22, 2019 at 11:34:33AM +0100, Suzuki K Poulose wrote:
> This series adds the support for CoreSight devices on ACPI based
> platforms. The device connections are encoded as _DSD graph property[0],
> with CoreSight specific extensions to indicate the direction of data
> flow as described in [1]. Components attached to CPUs are listed
> as child devices of the corresponding CPU, removing explicit links
> to the CPU like we do in the DT.
> 
> The majority of the series cleans up the driver and prepares the subsystem
> for platform agnostic firwmare probing, naming scheme, searching etc.
> 
> We introduce platform independent helpers to parse the platform supplied
> information. Thus we rename the platform handling code from:
> 	of_coresight.c  => coresight-platform.c
> 
> The CoreSight driver creates shadow devices that appear on the Coresight
> bus, in addition to the real devices (e.g, AMBA bus devices). The name
> of these devices match the real device. This makes the device name
> a bit cryptic for ACPI platform. So this series also introduces a generic
> platform agnostic device naming scheme for the shadow Coresight devices.
> Towards this we also make changes to the way we lookup devices to resolve
> the connections, as we can't use the names to identify the devices. So,
> we use the "fwnode_handle" of the real device for the device lookups.
> Towards that we clean up the drivers to keep track of the "CoreSight"
> device rather than the "real" device. However, all real operations,
> like DMA allocation, Power management etc. must be performed on
> the real device which is the parent of the shadow device.
> 
> Finally we add the support for parsing the ACPI platform data. The power
> management support is missing in the ACPI (and this is not specific to
> CoreSight). The firmware must ensure that the respective power domains
> are turned on.
> 
> Applies on v5.2-rc1
> 
> Tested on a Juno-r0 board with ACPI bindings patch (Patch 31/30) added on
> top of [2]. You would need to make sure that the debug power domain is
> turned on before the Linux kernel boots. (e.g, connect the DS-5 to the
> Juno board while at UEFI). arm32 code is only compile tested.

After I applied this patch set, I found all device names under
'/sys/bus/event_source/devices/cs_etm/sinks/' have been changed as
below on my DB410c board:
# ls /sys/bus/event_source/devices/cs_etm/sinks/
tmc_etf0  tmc_etr0  tpiu0

This leads to below command failure when open PMU device:
# perf record -e cs_etm/@...000.etr/ --per-thread uname
failed to set sink "826000.etr" on event cs_etm/@...000.etr/ with 2 (No such file or directory)

I must use below command so that perf can match string with the
device name under '/sys/bus/event_source/devices/cs_etm/sinks/':
# perf record -e cs_etm/@..._etr0/ --per-thread uname

Seems to me, this is an unexpected change and when I worked on the
patch set v2, IIRC that version still can use '826000.etr' to open PMU
device.

Please help confirm for this.  Thanks!

Leo.