Re: [PATCH RESEND 0/4] Add support for HiSilicon PCIe Tune and Trace device

[Suzuki K Poulose]

On 19/04/2021 14:21, Yicong Yang wrote:
> On 2021/4/19 19:17, Suzuki K Poulose wrote:
> > On 17/04/2021 11:17, Yicong Yang wrote:
> > > [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.
> >
> > ...
> >
> > > 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.
> >
> > Please use perf. Debugfs / sysfs is not the right place for these things.
>
> ok.
>
> > Also, please move your driver to drivers/perf/
>
> Does it make sense as it's a tuning and tracing device, and doesn't have counters
> nor do the sampling like usual PMU device under drivers/perf/.

It doesn't matter. As long as you can drive it via the perf interface,
it can live there. The CoreSight was added way before there was kind
of a suitable place like the above. You could find other uncore PMUs
under drivers/perf.

Suzuki