linux-kernel - Re: [RFC PATCH 0/5] PCIe EPF support for internal DMAC handling and driver update for R-Car PCIe EP to support DMAC

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Date:   Thu, 10 Feb 2022 18:52:16 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     "Lad, Prabhakar" <prabhakar.csengg@...il.com>
Cc:     Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
        Kishon Vijay Abraham I <kishon@...com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Marek Vasut <marek.vasut+renesas@...il.com>,
        Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
        Rob Herring <robh@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Linux-Renesas <linux-renesas-soc@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Biju Das <biju.das.jz@...renesas.com>
Subject: Re: [RFC PATCH 0/5] PCIe EPF support for internal DMAC handling and
 driver update for R-Car PCIe EP to support DMAC

On Thu, Feb 10, 2022 at 11:05:45AM +0000, Lad, Prabhakar wrote:
> On Thu, Feb 10, 2022 at 10:50 AM Manivannan Sadhasivam
> <manivannan.sadhasivam@...aro.org> wrote:
> >
> > On Thu, Feb 10, 2022 at 09:24:19AM +0000, Lad, Prabhakar wrote:
> > > Hi,
> > >
> > > On Thu, Feb 10, 2022 at 8:40 AM Manivannan Sadhasivam
> > > <manivannan.sadhasivam@...aro.org> wrote:
> > > >
> > > > Hi,
> > > >
> > > > On Wed, Jan 26, 2022 at 07:50:38PM +0000, Lad Prabhakar wrote:
> > > > > Hi All,
> > > > >
> > > > > The current PCIe EPF framework supports DMA data transfers using external
> > > > > DMA only, this patch series aims to add support for platforms supporting
> > > > > internal DMAC on PCIe for data transfers.
> > > > >
> > > > > R-Car PCIe supports internal DMAC to transfer data between Internal Bus to
> > > > > PCI Express and vice versa. Last patch fills up the required flags and ops
> > > > > to support internal DMAC.
> > > > >
> > > > > Patches 1-3 are for PCIe EPF core to support internal DMAC handling, patch
> > > > > 4/5 is to fix test cases based on the conversation [1].
> > > > >
> > > >
> > > > This looks similar to the Synopsys eDMA IP [1] that goes with the Synopsys PCIe
> > > > endpoint IP. Why can't you represent it as a dmaengine driver and use the
> > > > existing DMA support?
> > > >
> > > Let me have a look. Could you please share a link to the Synopsys PCIe
> > > endpoint HW manual (the driver doesn't have a binding doc).
> > >
> >
> > I don't think the PCIe reference manual is available publicly. And you are right
> > that the driver is not tied to devicetree. The reason is, it gets probed using
> > the PCI ID of the EP and all the resources are defined statically in the driver
> > itself.
> >
> In R-Car PCIe the internal dmac is part of the PCIe block itself [0]
> and not a separate block. I don't see any drivers implementing the
> internal dmac drivers as a DMA engine driver. For example the Renesas
> SDHI driver has internal dmac too, this is handled in the SDHI driver
> itself [1] and not implemented as DMA engine driver. Let me know if my
> understanding is wrong here.
> 

Okay, thanks for the clarification. I thought that if the IP is same, we could
implement it as a standalone DMA engine driver, but looks like it is customized.
So I guess it is reasonable to have an internal implementation.

Thanks,
Mani

> [0] https://elixir.bootlin.com/linux/v5.17-rc3/source/Documentation/devicetree/bindings/pci/rcar-pci-ep.yaml#L76
> [1] https://elixir.bootlin.com/linux/v5.17-rc3/source/drivers/mmc/host/renesas_sdhi_internal_dmac.c
> 
> Cheers,
> Prabhakar
> 
> > Thanks,
> > Mani
> >
> > > Cheers,
> > > Prabhakar
> > >
> > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/dma/dw-edma
> > > >
> > > > > Patches are based on top of [1] next branch.
> > > > >
> > > > > [0] https://www.spinics.net/lists/linux-pci/msg92385.html
> > > > > [1] https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git
> > > > >
> > > > > Cheers,
> > > > > Prabhakar
> > > > >
> > > > > Lad Prabhakar (5):
> > > > >   PCI: endpoint: Add ops and flag to support internal DMAC
> > > > >   PCI: endpoint: Add support to data transfer using internal dmac
> > > > >   misc: pci_endpoint_test: Add driver data for Renesas RZ/G2{EHMN}
> > > > >   misc: pci_endpoint_test: Add support to pass flags for buffer
> > > > >     allocation
> > > > >   PCI: rcar-ep: Add support for DMAC
> > > > >
> > > > >  drivers/misc/pci_endpoint_test.c              |  56 ++++-
> > > > >  drivers/pci/controller/pcie-rcar-ep.c         | 227 ++++++++++++++++++
> > > > >  drivers/pci/controller/pcie-rcar.h            |  23 ++
> > > > >  drivers/pci/endpoint/functions/pci-epf-test.c | 184 ++++++++++----
> > > > >  drivers/pci/endpoint/pci-epf-core.c           |  32 +++
> > > > >  include/linux/pci-epc.h                       |   8 +
> > > > >  include/linux/pci-epf.h                       |   7 +
> > > > >  7 files changed, 483 insertions(+), 54 deletions(-)
> > > > >
> > > > > --
> > > > > 2.25.1
> > > > >