RE: [PATCH v2] staging: fsl-mc: add DPAA2 overview readme
From: Stuart Yoder
Date: Mon Aug 10 2015 - 22:54:39 EST
> -----Original Message-----
> From: Alexander Graf [mailto:agraf@xxxxxxx]
> Sent: Sunday, August 09, 2015 9:25 AM
> To: Yoder Stuart-B08248; gregkh@xxxxxxxxxxxxxxxxxxx; Rivera Jose-B46482; katz Itai-RM05202
> Cc: devel@xxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; arnd@xxxxxxxx
> Subject: Re: [PATCH v2] staging: fsl-mc: add DPAA2 overview readme
>
>
>
> On 07.08.15 03:09, Stuart Yoder wrote:
> > add README file providing an overview of the DPAA2 architecture
> > and how it is integrated in Linux
> >
> > Signed-off-by: Stuart Yoder <stuart.yoder@xxxxxxxxxxxxx>
> > ---
> > -v2: added changelog text
> >
> > drivers/staging/fsl-mc/README.txt | 364 ++++++++++++++++++++++++++++++++++++++
> > drivers/staging/fsl-mc/TODO | 4 -
> > 2 files changed, 364 insertions(+), 4 deletions(-)
> > create mode 100644 drivers/staging/fsl-mc/README.txt
> >
> > diff --git a/drivers/staging/fsl-mc/README.txt b/drivers/staging/fsl-mc/README.txt
> > new file mode 100644
> > index 0000000..8214102
> > --- /dev/null
> > +++ b/drivers/staging/fsl-mc/README.txt
> > @@ -0,0 +1,364 @@
> > +Copyright (C) 2015 Freescale Semiconductor Inc.
> > +
> > +DPAA2 (Data Path Acceleration Architecture Gen2)
> > +------------------------------------------------
> > +
> > +This document provides an overview of the Freescale DPAA2 architecture
> > +and how it is integrated into the Linux kernel.
> > +
> > +Contents summary
> > + -DPAA2 overview
> > + -Overview of DPAA2 objects
> > + -DPAA2 Linux driver architecture overview
> > + -bus driver
> > + -dprc driver
> > + -allocator
> > + -dpio driver
> > + -Ethernet
> > + -mac
> > +
> > +DPAA2 Overview
> > +--------------
> > +
> > +DPAA2 is a hardware architecture designed for high-speeed network
> > +packet processing. DPAA2 consists of sophisticated mechanisms for
> > +processing Ethernet packets, queue management, buffer management,
> > +autonomous L2 switching, virtual Ethernet bridging, and accelerator
> > +(e.g. crypto) sharing.
> > +
> > +A DPAA2 hardware component called the Management Complex (or MC) manages the
> > +DPAA2 hardware resources. The MC provides an object-based abstraction for
> > +software drivers to use the DPAA2 hardware.
> > +
> > +The MC uses DPAA2 hardware resources such as queues, buffer pools, and
> > +network ports to create functional objects/devices such as network
> > +interfaces, an L2 switch, or accelerator instances.
> > +
> > +The MC provides memory-mapped I/O command interfaces (MC portals)
> > +which DPAA2 software drivers use to operate on DPAA2 objects:
> > +
> > + +--------------------------------------+
> > + | OS |
> > + | DPAA2 drivers |
> > + | | |
> > + +-----------------------------|--------+
> > + |
> > + | (create,discover,connect
> > + | config,use,destroy)
> > + |
> > + DPAA2 |
> > + +------------------------| mc portal |-+
> > + | | |
> > + | +- - - - - - - - - - - - -V- - -+ |
> > + | | | |
> > + | | Management Complex (MC) | |
> > + | | | |
> > + | +- - - - - - - - - - - - - - - -+ |
> > + | |
> > + | Hardware Hardware |
> > + | Resources Objects |
> > + | --------- ------- |
> > + | -queues -DPRC |
> > + | -buffer pools -DPMCP |
> > + | -Eth MACs/ports -DPIO |
> > + | -network interface -DPNI |
> > + | profiles -DPMAC |
> > + | -queue portals -DPBP |
> > + | -MC portals ... |
> > + | ... |
> > + | |
> > + +--------------------------------------+
> > +
> > +The MC mediates operations such as create, discover,
> > +connect, configuration, and destroy. Fast-path operations
> > +on data, such as packet transmit/receive, are not mediated by
> > +the MC and are done directly using memory mapped regions in
> > +DPIO objects.
> > +
> > +Overview of DPAA2 Objects
> > +-------------------------
> > +The section provides a brief overview of some key objects
> > +in the DPAA2 hardware. A simple scenario is described illustrating
> > +the objects involved in creating a network interfaces.
> > +
> > +-DPRC (Datapath Resource Container)
> > +
> > + A DPRC is an container object that holds all the other
> > + types of DPAA2 objects. In the example diagram below there
> > + are 8 objects of 5 types (DPMCP, DPIO, DPBP, DPNI, and DPMAC)
> > + in the container.
> > +
> > + +---------------------------------------------------------+
> > + | DPRC |
> > + | |
> > + | +-------+ +-------+ +-------+ +-------+ +-------+ |
> > + | | DPMCP | | DPIO | | DPBP | | DPNI | | DPMAC | |
> > + | +-------+ +-------+ +-------+ +---+---+ +---+---+ |
> > + | | DPMCP | | DPIO | |
> > + | +-------+ +-------+ |
> > + | | DPMCP | |
> > + | +-------+ |
> > + | |
> > + +---------------------------------------------------------+
> > +
> > + From the point of view of an OS, a DPRC is bus-like. Like
> > + a plug-and-play bus, such as PCI, DPRC commands can be used to
> > + enumerate the contents of the DPRC, discover the hardware
> > + objects present (including mappable regions and interrupts).
> > +
> > + dprc.1 (bus)
> > + |
> > + +--+--------+-------+-------+-------+
> > + | | | | |
> > + dpmcp.1 dpio.1 dpbp.1 dpni.1 dpmac.1
> > + dpmcp.2 dpio.2
> > + dpmcp.3
> > +
> > + Hardware objects can be created and destroyed dynamically, providing
> > + the ability to hot plug/unplug objects in and out of the DPRC.
> > +
> > + A DPRC has a mappable mmio region (an MC portal) that can be used
> > + to send MC commands. It has an interrupt for status events (like
> > + hotplug).
> > +
> > + All objects in a container share the same hardware "isolation context".
> > + This means that with respect to an IOMMU the isolation granularity
> > + is at the DPRC (container) level, not at the individual object
> > + level.
> > +
> > + DPRCs can be defined statically and populated with objects
> > + via a config file passed to the MC when firmware starts
> > + it. There is also a Linux user space tool called "restool"
> > + that can be used to create/destroy containers and objects
> > + dynamically.
>
> Is this tool publicly available yet?
Not yet.
> Also, I find the naming unfortunate
> for a tool that potentially will get included in general purpose
> distributions. Naming it "dpaa2-restool" for example would make it much
> clearer what its purpose is and would give you a nice namespace to add
> more tools to later.
Probably a good idea.
> > +
> > +-DPAA2 Objects for an Ethernet Network Interface
> > +
> > + A typical Ethernet NIC is monolithic-- the NIC device contains TX/RX
> > + queuing mechanisms, configuration mechanisms, buffer management,
> > + physical ports, and interrupts. DPAA2 uses a more granular approach
> > + utilizing multiple hardware objects. Each object has specialized
> > + functions, and are used together by software to provide Ethernet network
> > + interface functionality. This approach provides efficient use of finite
> > + hardware resources, flexibility, and performance advantages.
> > +
> > + The diagram below shows the objects needed for a simple
> > + network interface configuration on a system with 2 CPUs.
> > +
> > + +---+---+ +---+---+
> > + CPU0 CPU1
> > + +---+---+ +---+---+
> > + | |
> > + +---+---+ +---+---+
> > + DPIO DPIO
> > + +---+---+ +---+---+
> > + \ /
> > + \ /
> > + \ /
> > + +---+---+
> > + DPNI --- DPBP,DPMCP
> > + +---+---+
> > + |
> > + |
> > + +---+---+
> > + DPMAC
> > + +---+---+
> > + |
> > + port/PHY
> > +
> > + Below the objects are described. For each object a brief description
> > + is provided along with a summary of the kinds of operations the object
> > + supports and a summary of key resources of the object (mmio regions
> > + and irqs).
> > +
> > + -DPMAC (Datapath Ethernet MAC): represents an Ethernet MAC, a
> > + hardware device that connects to an Ethernet PHY and allows
> > + physical transmission and reception of Ethernet frames.
> > + -mmio regions: none
> > + -irqs: dpni link change
> > + -commands: set link up/down, link config, get stats,
> > + irq config, enable, reset
> > +
> > + -DPNI (Datapath Network Interface): contains TX/RX queues,
> > + network interface configuration, and rx buffer pool configuration
> > + mechanisms.
> > + -mmio regions: none
> > + -irqs: link state
> > + -commands: port config, offload config, queue config,
> > + parse/classify config, irq config, enable, reset
> > +
> > + -DPIO (Datapath I/O): provides interfaces to enqueue and dequeue
> > + packets and do hardware buffer pool management operations. For
>
> I think you may want to explain the difference between TX/RX queues and
> "interfaces to enqueue and dequeue packets" ;).
So, the queues are literally just the queues themselves (identified by
queue #). They are accessible via the DPIO mmio region. So to enqueue
something you write a descriptor to the DPIO mmio region, which includes
the target queue #.
So the architecture separates the interface to access the queues from
the queues themselves. DPIOs are intended to be shared among all
DPAA2 drivers in the kernel that interact with queues.
Since a CPU can only do one thing at a time, you just need 1 DPIO
queuing interface per CPU for optimal performance. But, there are
thousands of queues that could exists in the system.
Will expand the description to clarify this.
> > + optimum performance there is typically DPIO per CPU. This allows
>
> typically [one] DPIO?
Yes, as mentioned above, one DPIO per CPU is optimal. But, you could
have just 1 DPIO period and 8 cpus sharing it.
> > + each CPU to perform simultaneous enqueue/dequeue operations.
> > + -mmio regions: queue operations, buffer mgmt
> > + -irqs: data availability, congestion notification, buffer
> > + pool depletion
> > + -commands: irq config, enable, reset
> > +
> > + -DPBP (Datapath Buffer Pool): represents a hardware buffer
> > + pool.
> > + -mmio regions: none
> > + -irqs: none
> > + -commands: enable, reset
> > +
> > + -DPMCP (Datapath MC Portal): provides an MC command portal.
> > + Used by drivers to send commands to the MC to manage
> > + objects.
> > + -mmio regions: MC command portal
> > + -irqs: command completion
> > + -commands: irq config, enable, reset
> > +
> > + Object Connections
> > + ------------------
> > + Some objects have explicit relationships that must
> > + be configured:
> > +
> > + -DPNI <--> DPMAC
> > + -DPNI <--> DPNI
> > + -DPNI <--> L2-switch-port
> > + A DPNI must be connected to something such as a DPMAC,
> > + another DPNI, or L2 switch port. The DPNI connection
> > + is made via a DPRC command.
> > +
> > + +-------+ +-------+
> > + | DPNI | | DPMAC |
> > + +---+---+ +---+---+
> > + | |
> > + +==========+
> > +
> > + -DPNI <--> DPBP
> > + A network interface requires a 'buffer pool' (DPBP
> > + object) which provides a list of pointers to memory
> > + where received Ethernet data is to be copied. The
> > + Ethernet driver configures the DPBPs associated with
> > + the network interface.
> > +
> > + Interrupts
> > + ----------
> > + All interrupts generated by DPAA2 objects are message
> > + interrupts. At the hardware level message interrupts
> > + generated by devices will normally have 3 components--
> > + 1) a non-spoofable 'device-id' expressed on the hardware
> > + bus, 2) an address, 3) a data value.
> > +
> > + In the case of DPAA2 devices/objects, all objects in the
> > + same container/DPRC share the same 'device-id'.
> > + For ARM-based SoC this is the same as the stream ID.
> > +
> > +
> > +DPAA2 Linux Driver Overview
> > +---------------------------
> > +
> > +This section provides an overview of the Linux kernel drivers for
> > +DPAA2-- 1) the bus driver and associated "DPAA2 infrastructure"
> > +drivers and 2) functional object drivers (such as Ethernet).
> > +
> > +As described previously, a DPRC is a container that holds the other
> > +types of DPAA2 objects. It is functionally similar to a plug-and-play
> > +bus controller.
> > +
> > +Each object in the DPRC is a Linux "device" and is bound to a driver.
> > +The diagram below shows the Linux drivers involved in a networking
> > +scenario and the objects bound to each driver. A brief description
> > +of each driver follows.
> > +
> > + +------------+
> > + | OS Network |
> > + | Stack |
> > + +------------+ +------------+
> > + | Allocator |. . . . . . . | Ethernet |
> > + |(dpmcp,dpbp)| | (dpni) |
> > + +-.----------+ +---+---+----+
> > + . . ^ |
> > + . . <data avail, | |<enqueue,
> > + . . tx confirm> | | dequeue>
> > + +-------------+ . | |
> > + | DPRC driver | . +---+---V----+ +---------+
> > + | (dprc) | . . . . . .| DPIO driver| | MAC |
> > + +----------+--+ | (dpio) | | (dpmac) |
> > + | +------+-----+ +-----+---+
> > + |<dev add/remove> | |
> > + | | |
> > + +----+--------------+ | +--+---+
> > + | mc-bus driver | | | PHY |
> > + | | | |driver|
> > + | /fsl-mc@80c000000 | | +--+---+
> > + +-------------------+ | |
> > + | |
> > + ================================ HARDWARE =========|=================|======
> > + DPIO |
> > + | |
> > + DPNI---DPBP |
> > + | |
> > + DPMAC |
> > + | |
> > + PHY ---------------+
> > + ===================================================|========================
> > +
> > +A brief description of each driver is provided below.
> > +
> > + mc-bus driver
> > + -------------
> > + The mc-bus driver is a platform driver and is probed from an
> > + "/fsl-mc@xxxx" node in the device tree passed in by boot firmware.
>
> Probably better to describe the actual binding here which is based on
> compatible.
Ok
> > + It is responsible for bootstrapping the DPAA2 kernel infrastructure.
> > + Key functions include:
> > + -registering a new bus type named "fsl-mc" with the kernel,
> > + and implementing bus call-backs (e.g. match/uevent/dev_groups)
> > + -implemeting APIs for DPAA2 driver registration and for device
>
> implemeting? ;)
Thanks...
> > + add/remove
> > + -creates an MSI irq domain
> > + -do a device add of the 'root' DPRC device, which is needed
> > + to bootstrap things
>
> I think you can find a better way to describe exposure of the root
> container than "to bootstrap things".
Runtime management of the DPRC/container is by the "DPRC driver" (see
below). That driver scans the bus, does device_add() operations,
handles hotplug events.
But, how did that DPRC itself driver start? It _is_ a DPAA2 driver as
well... how did the device_add() happen for the root DPRC object? That is the
bootstrapping role of the mc-bus driver. It manufactures the device info
needed to add a device to the bus, calls device_add, which in turn causes
the DPRC driver to get probed, and things start from there.
After that initial boostrapping, the mc-bus platform driver never does
anything again.
Did that help? If so, I'll try to clarify the text. If it still is unclear
I'll try to explain more.
> > +
> > + DPRC driver
> > + -----------
> > + The dprc-driver is bound DPRC objects and does runtime management
>
> bound [to] DPRC
Thanks...
> > + of a bus instance. It performs the initial bus scan of the DPRC
> > + and handles interrupts for container events such as hot plug.
> > +
> > + Allocator
> > + ----------
> > + Certain objects such as DPMCP and DPBP are generic and fungible,
> > + and are intended to be used by other drivers. For example,
> > + the DPAA2 Ethernet driver needs:
> > + -DPMCPs to send MC commands, to configure network interfaces
> > + -DPBPs for network buffer pools
> > +
> > + The allocator driver registers for these allocatable object types
> > + and those objects are bound to the allocator when the bus is probed.
> > + The allocator maintains a pool of objects that are available for
> > + allocation by other DPAA2 drivers.
> > +
> > + DPIO driver
> > + -----------
> > + The DPIO driver is bound to DPIO objects and provides services that allow
> > + other drivers such as the Ethernet driver to receive and transmit data.
> > + Key services include:
> > + -data availability notifications
> > + -hardware queuing operations (enqueue and dequeue of data)
> > + -hardware buffer pool management
> > +
> > + There is typically one DPIO object per physical CPU for optimum
> > + performance, allowing each CPU to simultaneously enqueue
> > + and dequeue data.
> > +
> > + The DPIO driver operates on behalf of all DPAA2 drivers
> > + active in the kernel-- Ethernet, crypto, compression,
> > + etc.
>
> I'm not quite sure what this means? Where do I MMIO into when I want to
> transmit a packet?
The MMIO region is in the DPIO, but you (e.g. Ethernet) don't touch it
directly. You call a DPIO driver API (lightweight). The DPIO driver provides
APIs to put/get data on/from queues for all drivers that access the queuing
system-- Ethernet, crypto, compression, pattern matcher, etc.
Thanks,
Stuart
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