linux-kernel - Re: Support for configurable PCIe endpoint

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Message-ID: <57A31299.2040805@ti.com>
Date:	Thu, 4 Aug 2016 15:32:01 +0530
From:	Kishon Vijay Abraham I <kishon@...com>
To:	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

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.

Thanks
Kishon