RE: [PATCH v2 0/3] Add support for RAS DES feature in PCIe DW controller

["Shradha Todi" <shradha.t@samsung.com>]

> -----Original Message-----
> From: Manivannan Sadhasivam [mailto:manivannan.sadhasivam@linaro.org]
> Sent: 30 November 2023 22:25
> To: Shradha Todi <shradha.t@samsung.com>
> Cc: lpieralisi@kernel.org; kw@linux.com; robh@kernel.org;
> bhelgaas@google.com; jingoohan1@gmail.com;
> gustavo.pimentel@synopsys.com; josh@joshtriplett.org;
> lukas.bulwahn@gmail.com; hongxing.zhu@nxp.com;
> pankaj.dubey@samsung.com; linux-kernel@vger.kernel.org; linux-
> pci@vger.kernel.org
> Subject: Re: [PATCH v2 0/3] Add support for RAS DES feature in PCIe DW
> controller
> 
> On Thu, Nov 30, 2023 at 05:20:41PM +0530, Shradha Todi wrote:
> > DesignWare controller provides a vendor specific extended capability
> > called RASDES as an IP feature. This extended capability  provides
> > hardware information like:
> >  - Debug registers to know the state of the link or controller.
> >  - Error injection mechanisms to inject various PCIe errors including
> >    sequence number, CRC
> >  - Statistical counters to know how many times a particular event
> >    occurred
> >
> > However, in Linux we do not have any generic or custom support to be
> > able to use this feature in an efficient manner. This is the reason we
> > are proposing this framework. Debug and bring up time of high-speed
> > IPs are highly dependent on costlier hardware analyzers and this
> > solution will in some ways help to reduce the HW analyzer usage.
> >
> > The debugfs entries can be used to get information about underlying
> > hardware and can be shared with user space. Separate debugfs entries
> > has been created to cater to all the DES hooks provided by the controller.
> > The debugfs entries interacts with the RASDES registers in the
> > required sequence and provides the meaningful data to the user. This
> > eases the effort to understand and use the register information for
> debugging.
> >
> > v1 version was posted long back and for some reasons I couldn't work
> > on it. I apologize for the long break. I'm restarting this activity
> > and have taken care of all previous review comments shared.
> > v1:
> > https://lore.kernel.org/all/20210518174618.42089-1-shradha.t@samsung.c
> > om/T/
> >
> 
> There is already a series floating to add similar functionality via perf
> subsystem: https://lore.kernel.org/linux-pci/20231121013400.18367-1-
> xueshuai@linux.alibaba.com/
> 
> - Mani
> 

Hi Mani,

The series proposed in perf includes only time based-analysis and event counters which will monitor performance (Group 6 and 7). The patch or framework that we have proposed includes debug information, error injection facility and error counters (Group 0 - 5) which are not included as part of the functionality implemented via perf. In my opinion, these functionalities don't count as performance monitoring or counters but rather as debug counters. How about we take this up as a debugfs framework as proposed in my patch? 
Or if others feel it can be taken via perf driver then I am happy to extend the perf driver if authors do not have objection. Let me know what you think of this? Meanwhile I will review the perf patches and share my feedback.

> > Shradha Todi (3):
> >   PCI: dwc: Add support for vendor specific capability search
> >   PCI: debugfs: Add support for RASDES framework in DWC
> >   PCI: dwc: Create debugfs files in DWC driver
> >
> >  drivers/pci/controller/dwc/Kconfig            |   8 +
> >  drivers/pci/controller/dwc/Makefile           |   1 +
> >  .../controller/dwc/pcie-designware-debugfs.c  | 476
> ++++++++++++++++++
> >  .../controller/dwc/pcie-designware-debugfs.h  |   0
> >  drivers/pci/controller/dwc/pcie-designware.c  |  20 +
> > drivers/pci/controller/dwc/pcie-designware.h  |  18 +
> >  6 files changed, 523 insertions(+)
> >  create mode 100644
> > drivers/pci/controller/dwc/pcie-designware-debugfs.c
> >  create mode 100644
> > drivers/pci/controller/dwc/pcie-designware-debugfs.h
> >
> > --
> > 2.17.1
> >
> 
> --
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