[RESEND with perf and coresight folks Cc'ed] HiSilicon PCIe tune and trace device (PTT) is a PCIe Root Complex integrated Endpoint (RCiEP) device, providing the capability to dynamically monitor and tune the PCIe traffic (tune), and trace the TLP headers (trace). PTT tune is designed for monitoring and adjusting PCIe link parameters. We provide several parameters of the PCIe link. Through the driver, user can adjust the value of certain parameter to affect the PCIe link for the purpose of enhancing the performance in certian situation. PTT trace is designed for dumping the TLP headers to the memory, which can be used to analyze the transactions and usage condition of the PCIe Link. Users can choose filters to trace headers, by either requester ID, or those downstream of a set of Root Ports on the same core of the PTT device. It's also supported to trace the headers of certain type and of certain direction. We use debugfs to expose the interface. For tune, one parameter is a debugfs file and user can set/get the value by reading/writing the file. For trace, we have several control files for the user to configure the trace parameters like filters, TLP type and format, the desired trace data size and so on. There is one data file for dumping the traced data to the user. The traced data maybe hundreds of megabytes so sysfs cannot support. The reason for debugfs rather than character device is that we don't want to have additional userspace tools. The operation through debugfs is easier and a bit like ftrace. The reason for not using perf is because there is no current support for uncore tracing in the perf facilities. We have our own format of data and don't need perf doing the parsing. The setting through perf tools doesn't seem to be friendly as well. For example, we cannot count on perf to decode the usual format BDF number like <domain>:<bus>:<dev>.<fn>, which user can use to filter the TLP headers through the PTT device. A similar approach for implementing this function is ETM, which use sysfs for configuring and a character device for dumping data. Greg has some comments on our implementation and doesn't advocate to build driver on debugfs [1]. So I resend this series to collect more feedbacks on the implementation of this driver. Hi perf and ETM related experts, is it suggested to adapt this driver to perf? Or is the debugfs approach acceptable? Otherwise use sysfs + character device like ETM and use perf tools for decoding it? Any comments is welcomed. [1] https://lore.kernel.org/linux-pci/1617713154-35533-1-git-send-email-yangyicong@xxxxxxxxxxxxx/ Yicong Yang (4): hwtracing: Add trace function support for HiSilicon PCIe Tune and Trace device hwtracing: Add tune function support for HiSilicon PCIe Tune and Trace device docs: Add HiSilicon PTT device driver documentation MAINTAINERS: Add maintainer for HiSilicon PTT driver Documentation/trace/hisi-ptt.rst | 326 +++++++ MAINTAINERS | 7 + drivers/Makefile | 1 + drivers/hwtracing/Kconfig | 2 + drivers/hwtracing/hisilicon/Kconfig | 11 + drivers/hwtracing/hisilicon/Makefile | 2 + drivers/hwtracing/hisilicon/hisi_ptt.c | 1636 ++++++++++++++++++++++++++++++++ 7 files changed, 1985 insertions(+) create mode 100644 Documentation/trace/hisi-ptt.rst create mode 100644 drivers/hwtracing/hisilicon/Kconfig create mode 100644 drivers/hwtracing/hisilicon/Makefile create mode 100644 drivers/hwtracing/hisilicon/hisi_ptt.c -- 2.8.1
