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Subject: Re: [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework
To:     Alan Mikhak <alan.mikhak@sifive.com>,
        Haotian Wang <haotian.wang@sifive.com>, <haotian.wang@duke.edu>
CC:     Gustavo Pimentel <Gustavo.Pimentel@synopsys.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
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        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
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        "palmer@sifive.com" <palmer@sifive.com>,
        "paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
        Vinod Koul <vkoul@kernel.org>
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From:   Kishon Vijay Abraham I <kishon@ti.com>
Message-ID: <40fafe93-d2dd-b1f5-bc16-cd84ff07bd13@ti.com>
Date:   Fri, 13 Sep 2019 17:41:23 +0530
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+ Haotian Wang

On 03/06/19 11:12 PM, Alan Mikhak wrote:
> On Sun, Jun 2, 2019 at 9:43 PM Kishon Vijay Abraham I <kishon@ti.com> wrote:
>> Hi Alan,
>> On 31/05/19 11:46 PM, Alan Mikhak wrote:
>>> On Thu, May 30, 2019 at 10:08 PM Kishon Vijay Abraham I <kishon@ti.com> wrote:
>>>> Hi Alan,
>>>>> Hi Kishon,
>>>>
>>>> I still have to look closer into your DMA patch but linked-list mode or single
>>>> block mode shouldn't be an user select-able option but should be determined by
>>>> the size of transfer.
>>>
>>> Please consider the following when taking a closer look at this patch.
>>
>> After seeing comments from Vinod and Arnd, it looks like the better way of
>> adding DMA support would be to register DMA within PCI endpoint controller to
>> DMA subsystem (as dmaengine) and use only dmaengine APIs in pci_epf_test.
> 
> Thanks Kishon. That makes it clear where these pieces should go.
> 
>>> In my specific use case, I need to verify that any valid block size,
>>> including a one byte transfer, can be transferred across the PCIe bus
>>> by memcpy_toio/fromio() or by DMA either as a single block or as
>>> linked-list. That is why, instead of deciding based on transfer size,
>>> this patch introduces the '-L' flag for pcitest to communicate the
>>> user intent across the PCIe bus to pci-epf-test so the endpoint can
>>> initiate the DMA transfer using a single block or in linked-list mode.
>> The -L option seems to select an internal DMA configuration which might be
>> specific to one implementation. As Gustavo already pointed, we should have only
>> generic options in pcitest. This would no longer be applicable when we move to
>> dmaengine.
> 
> Single-block DMA seemed as generic as linked-list DMA and
> memcpy_toio/fromio. It remains unclear how else to communicate that
> intent to pci_epf_test each time I invoke pcitest.
> 
> Regards,
> Alan
>