From: Joel Stanley <joel@jms.id.au>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Eddie James <eajames@linux.ibm.com>,
linux-aspeed <linux-aspeed@lists.ozlabs.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
DTML <devicetree@vger.kernel.org>,
Mark Rutland <mark.rutland@arm.com>,
Jason Cooper <jason@lakedaemon.net>,
Marc Zyngier <maz@kernel.org>, Rob Herring <robh+dt@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
Andrew Jeffery <andrew@aj.id.au>
Subject: Re: [PATCH v6 06/12] soc: aspeed: Add XDMA Engine Driver
Date: Mon, 16 Mar 2020 04:49:55 +0000 [thread overview]
Message-ID: <CACPK8XcD5O0dwEOSHqWfCu38B96JkdbcvzCuJhep+PXF6foC=g@mail.gmail.com> (raw)
In-Reply-To: <1a303336-9ffb-353f-efe3-7d45ed114fd0@linux.vnet.ibm.com>
On Mon, 10 Feb 2020 at 17:10, Eddie James <eajames@linux.vnet.ibm.com> wrote:
>
>
> On 2/10/20 10:35 AM, Arnd Bergmann wrote:
> > On Wed, Jan 15, 2020 at 10:31 PM Eddie James <eajames@linux.ibm.com> wrote:
> >> The XDMA engine embedded in the AST2500 and AST2600 SOCs performs PCI
> >> DMA operations between the SOC (acting as a BMC) and a host processor
> >> in a server.
> >>
> >> This commit adds a driver to control the XDMA engine and adds functions
> >> to initialize the hardware and memory and start DMA operations.
> >>
> >> Signed-off-by: Eddie James <eajames@linux.ibm.com>
> > Hi Eddie,
> >
> > I'm missing the bigger picture in the description here, how does this fit into
> > the PCIe endpoint framework and the dmaengine subsystem?
>
>
> Hi,
>
> It doesn't fit into the PCIe endpoint framework. The XDMA engine
> abstracts all the PCIe details away so the BMC cannot configure any of
> the things the PCIe endpoint exposes.
>
> It also doesn't fit into the dmaengine subsystem due to the restriction
> on the ast2500 (and maybe the ast2600) that the XDMA engine can only
> access certain areas of physical memory. Also problematic would be
> pausing/resuming/terminating transfers because the XDMA engine can't do
> those things.
>
>
> >
> > Does the AST2500 show up as a PCIe device in the host, or do you just
> > inject DMAs into the host and hope that bypasses the IOMMU?
> > If it shows up as an endpoint, how does the endpoint driver link into the
> > dma driver?
>
>
> The AST2500 and AST2600 have two PCIe devices on them, so these will
> show up on the host if the BMC enables both of them. Either or both can
> also be disabled and therefore will not show up. On the host side, in
> order to receive DMA transfers, its simply a matter of registering a PCI
> device driver and allocating some coherent DMA.... Not sure about the
> details of endpoints/dma client driver?
>
>
> Hopefully this answers your questions. Thanks,
Arnd, did you have further questions about this driver?
next prev parent reply other threads:[~2020-03-16 4:50 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 21:29 [PATCH v6 00/12] aspeed: Add SCU interrupt controller and XDMA engine drivers Eddie James
2020-01-15 21:29 ` [PATCH v6 01/12] dt-bindings: interrupt-controller: Add Aspeed SCU interrupt controller Eddie James
2020-01-15 21:29 ` [PATCH v6 02/12] irqchip: " Eddie James
2020-01-15 21:29 ` [PATCH v6 03/12] ARM: dts: aspeed: ast2500: Add " Eddie James
2020-01-15 21:29 ` [PATCH v6 04/12] ARM: dts: aspeed: ast2600: Add SCU interrupt controllers Eddie James
2020-01-15 21:29 ` [PATCH v6 05/12] dt-bindings: soc: Add Aspeed XDMA Engine Eddie James
2020-01-17 0:01 ` Andrew Jeffery
2020-01-15 21:29 ` [PATCH v6 06/12] soc: aspeed: Add XDMA Engine Driver Eddie James
2020-01-17 0:07 ` Andrew Jeffery
2020-02-10 16:35 ` Arnd Bergmann
2020-02-10 17:10 ` Eddie James
2020-03-16 4:49 ` Joel Stanley [this message]
2020-02-16 23:56 ` Andrew Jeffery
2020-01-15 21:29 ` [PATCH v6 07/12] soc: aspeed: xdma: Add user interface Eddie James
2020-01-17 0:09 ` Andrew Jeffery
2020-01-15 21:29 ` [PATCH v6 08/12] soc: aspeed: xdma: Add reset ioctl Eddie James
2020-01-15 21:29 ` [PATCH v6 09/12] ARM: dts: aspeed: ast2500: Add XDMA Engine Eddie James
2020-01-15 21:29 ` [PATCH v6 10/12] ARM: dts: aspeed: ast2600: " Eddie James
2020-01-15 21:29 ` [PATCH v6 11/12] ARM: dts: aspeed: witherspoon: Enable " Eddie James
2020-01-17 0:12 ` Andrew Jeffery
2020-01-15 21:29 ` [PATCH v6 12/12] ARM: dts: aspeed: tacoma: Enable XDMA engine Eddie James
2020-01-17 0:13 ` Andrew Jeffery
2020-01-20 8:54 ` [PATCH v6 00/12] aspeed: Add SCU interrupt controller and XDMA engine drivers Marc Zyngier
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