Re: Support for configurable PCIe endpoint

[Kishon Vijay Abraham I <kishon@ti.com>]

Hi Arnd,

On Thursday 25 August 2016 06:29 PM, Arnd Bergmann wrote:
> On Thursday, August 18, 2016 6:44:09 PM CEST Kishon Vijay Abraham I wrote:
>> Hi Arnd,
>>
>> On Thursday 04 August 2016 04:43 PM, Arnd Bergmann wrote:
>>> On Thursday, August 4, 2016 3:32:01 PM CEST Kishon Vijay Abraham I wrote:
>>>> On Wednesday 03 August 2016 07:09 PM, Joao Pinto wrote:
>>>>>
>>>>> 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.
>>>
>>>
>>> What's the difference between using the EDMA on that chip or a DMA engine
>>> that is part of the PCIe bridge?
>>
>> Do you mean the difference between using DMA on an EP (like ethernet card or
>> sata card) and DMA on PCI RC system? or is it the difference between eDMA
>> within the PCIe IP and system DMA?
> 
> The latter. You write that there is no DMA in the PCIe IP, but from the
> perspective of the RC, it should not matter whether the DMA engine is
> part of the EP logic or behind it.

right, from the RC perspective there is no difference.

What I meant is DMA support in PCIe driver has to be added newly (i.e for
designware) and the the platform I have doesn't have a DMA in PCIe IP. Anyways,
we'll come back to this later after I post my RFC series, maybe by this week end.

Thanks
Kishon