Message-ID: <20190529063449.GA15808@leoy-ThinkPad-X240s>
Date:   Wed, 29 May 2019 14:34:49 +0800
From:   Leo Yan <leo.yan@...aro.org>
To:     Mathieu Poirier <mathieu.poirier@...aro.org>
Cc:     Suzuki K Poulose <suzuki.poulose@....com>,
        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

On Tue, May 28, 2019 at 08:51:26AM -0600, Mathieu Poirier wrote:
> Good day,
> 
> On Tue, May 28, 2019 at 01:19:24PM +0800, Leo Yan wrote:
> > 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
> 
> Yes, that is the expected behavior.
> 
> > 
> > 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)
> 
> Correct.
> 
> > 
> > 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
> 
> Correct.
> 
> > 
> > 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.
> 
> Correct - v2 did not address the new naming convention for devices present under
> 'event_source', something that was corrected in v3.

Thanks for confirmation, Mathieu.

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