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

From: Alan Mikhak <alan.mikhak@sifive.com>
To: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Haotian Wang <haotian.wang@sifive.com>,
	haotian.wang@duke.edu,
	Gustavo Pimentel <Gustavo.Pimentel@synopsys.com>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"arnd@arndb.de" <arnd@arndb.de>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	"jingoohan1@gmail.com" <jingoohan1@gmail.com>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"wen.yang99@zte.com.cn" <wen.yang99@zte.com.cn>,
	"kjlu@umn.edu" <kjlu@umn.edu>,
	"linux-riscv@lists.infradead.org"
	<linux-riscv@lists.infradead.org>,
	"palmer@sifive.com" <palmer@sifive.com>,
	"paul.walmsley@sifive.com" <paul.walmsley@sifive.com>,
	Vinod Koul <vkoul@kernel.org>
Subject: Re: [PATCH] PCI: endpoint: Add DMA to Linux PCI EP Framework
Date: Fri, 13 Sep 2019 10:39:50 -0700	[thread overview]
Message-ID: <CABEDWGy3VdH40QAz5NVhQHLLXXf2C5W22uUXEw3yCeNz0hfF-Q@mail.gmail.com> (raw)
In-Reply-To: <40fafe93-d2dd-b1f5-bc16-cd84ff07bd13@ti.com>

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

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