linux-kernel - RE: Support for configurable PCIe endpoint

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Date:	Wed, 17 Aug 2016 09:49:20 +0000
From:	Mingkai Hu <mingkai.hu@....com>
To:	Kishon Vijay Abraham I <kishon@...com>,
	Joao Pinto <Joao.Pinto@...opsys.com>,
	"bhelgaas@...gle.com" <bhelgaas@...gle.com>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"arnd@...db.de" <arnd@...db.de>, Jingoo Han <jingoohan1@...il.com>,
	Pratyush Anand <pratyush.anand@...il.com>
CC:	Ley Foon Tan <lftan@...era.com>, Rob Herring <robh@...nel.org>,
	"Tanmay Inamdar" <tinamdar@....com>,
	Roy Zang <tie-fei.zang@...escale.com>,
	"Mingkai Hu" <mingkai.hu@...escale.com>,
	Minghuan Lian <minghuan.Lian@...escale.com>,
	Richard Zhu <Richard.Zhu@...escale.com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Murali Karicheri <m-karicheri2@...com>,
	"Thomas Petazzoni" <thomas.petazzoni@...e-electrons.com>,
	Jason Cooper <jason@...edaemon.net>,
	Thierry Reding <thierry.reding@...il.com>,
	"Simon Horman" <horms@...ge.net.au>,
	Zhou Wang <wangzhou1@...ilicon.com>,
	"Gabriele Paoloni" <gabriele.paoloni@...wei.com>,
	Stanimir Varbanov <svarbanov@...sol.com>,
	David Daney <david.daney@...ium.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
	Carlos Palminha <CARLOS.PALMINHA@...opsys.com>
Subject: RE: Support for configurable PCIe endpoint



> -----Original Message-----
> From: Kishon Vijay Abraham I [mailto:kishon@...com]
> Sent: Thursday, August 04, 2016 6:02 PM
> To: Joao Pinto <Joao.Pinto@...opsys.com>; bhelgaas@...gle.com; linux-
> pci@...r.kernel.org; arnd@...db.de; Jingoo Han <jingoohan1@...il.com>;
> Pratyush Anand <pratyush.anand@...il.com>
> Cc: Ley Foon Tan <lftan@...era.com>; Rob Herring <robh@...nel.org>;
> Tanmay Inamdar <tinamdar@....com>; Roy Zang <tie-
> fei.zang@...escale.com>; Mingkai Hu <mingkai.hu@...escale.com>;
> Minghuan Lian <minghuan.Lian@...escale.com>; Richard Zhu
> <Richard.Zhu@...escale.com>; Lucas Stach <l.stach@...gutronix.de>;
> Murali Karicheri <m-karicheri2@...com>; Thomas Petazzoni
> <thomas.petazzoni@...e-electrons.com>; Jason Cooper
> <jason@...edaemon.net>; Thierry Reding <thierry.reding@...il.com>;
> Simon Horman <horms@...ge.net.au>; Zhou Wang
> <wangzhou1@...ilicon.com>; Gabriele Paoloni
> <gabriele.paoloni@...wei.com>; Stanimir Varbanov <svarbanov@mm-
> sol.com>; David Daney <david.daney@...ium.com>; linux-
> kernel@...r.kernel.org; linux-arm-kernel@...ts.infradead.org; linux-
> omap@...r.kernel.org; Carlos Palminha
> <CARLOS.PALMINHA@...opsys.com>
> Subject: Re: Support for configurable PCIe endpoint
> 
> Hi,
> 
> On Wednesday 03 August 2016 07:09 PM, Joao Pinto wrote:
> > Hi Kishon,
> >
> > On 8/3/2016 7:03 AM, Kishon Vijay Abraham I wrote:
> >> Hi,
> >>
> >> The PCIe controller present in TI's DRA7 SoC is capable of operating
> >> either in Root Complex mode or Endpoint mode. (It uses Synopsys
> >> Designware Core). I'd assume most of the PCIe controllers on other
> >> platforms that use Designware core should also be capable to operate
> >> in endpoint mode. But linux kernel right now supports only RC mode.
> >>
> >> PCIe endpoint support discussion came up briefly before [1] but it
> >> was felt the practical use case will find firmware more suitable and
> >> endpoint support in kernel can be used only for validation or demo.
> >>
> >> *) Modify platform driver to support EP mode (in my case pci-dra7xx.c).
> >>
> >> *) dt binding specific to EP mode should be created.
> >>
> >> Once I complete the implementation and start posting RFC patches, a
> >> lot of these will become clear. But I want to check if this sounds
> >> okay to you guys before starting the implementation.
> >>
> >> Let me know if you have some other ideas too.
> >>
> >> Cheers
> >> Kishon
> >>
> >> [1] -> http://www.spinics.net/lists/linux-pci/msg26026.html
> >>
> >
> > You are rising a topic that we are also addressing in Synopsys.
> >
> > For the PCIe RC hardware validation we are currently using the
> > standard pcie-designware and pcie-designware-plat drivers.
> >
> > For the Endpoint we have to use an internal software package. Its main
> > purpose is to initialize the IP registers, eDMA channels and make data
> > transfer to prove that the everything is working properly. This is
> > done in 2 levels, a custom driver built and loaded and an application
> > that makes some ioctl to the driver executing some interesting
> > functions to check the Endpoint status and make some data exchange.
> 
> hmm.. the platform I have doesn't have a DMA in PCIe IP
> (http://www.ti.com/lit/ug/spruhz6g/spruhz6g.pdf). So in your testing does
> the EP access RC memory? i.e the driver in the RC allocates memory from it's
> DDR and gives it's DDR address to the EP. The EP then transfers data to this
> address. (This is a typical use case with ethernet PCIe cards). IIUC that's not
> simple with configurable EPs. I'd like to know more about your testing though.
> 

Hi Kishon,

This is a typical user case for EP to use DMA transfer data to/from RC memory.
In our case, we implement ring (like BD ring) or register in EP to communicate
The address allocated in RC memory, then EP can transfer data to/from RC memory.

Thanks,
Mingkai