linux-kernel - Re: [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework

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Date:   Fri, 13 Sep 2019 10:39:50 -0700
From:   Alan Mikhak <alan.mikhak@...ive.com>
To:     Kishon Vijay Abraham I <kishon@...com>
Cc:     Haotian Wang <haotian.wang@...ive.com>, haotian.wang@...e.edu,
        Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "arnd@...db.de" <arnd@...db.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "jingoohan1@...il.com" <jingoohan1@...il.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "wen.yang99@....com.cn" <wen.yang99@....com.cn>,
        "kjlu@....edu" <kjlu@....edu>,
        "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "paul.walmsley@...ive.com" <paul.walmsley@...ive.com>,
        Vinod Koul <vkoul@...nel.org>
Subject: Re: [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework

On Fri, Sep 13, 2019 at 5:11 AM Kishon Vijay Abraham I <kishon@...com> wrote:
>
> + 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@...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@...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
> >

Hi Kishon,

FYI, I integrated your changes for DMAengine client support to PCI
endpoint framework into my development branch. The following is the
link you provided earlier as reference. I have been using it with good
results. Haotian Wang also used it in a recent patch for PCI endpoint
function for virtnet. Would you be able to comment on if and when your
DMAengine client support may be submitted upstream?

http://git.ti.com/cgit/cgit.cgi/ti-linux-kernel/ti-linux-kernel.git/tree/drivers/pci/endpoint/pci-epf-core.c?h=ti-linux-4.19.y

Regards,
Alan Mikhak