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Message-ID: <55C9AA08.4000000@suse.de> Date: Tue, 11 Aug 2015 09:53:44 +0200 From: Alexander Graf <agraf@...e.de> To: Stuart Yoder <stuart.yoder@...escale.com>, "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>, Jose Rivera <German.Rivera@...escale.com>, Katz Itai <itai.katz@...escale.com> Cc: "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "arnd@...db.de" <arnd@...db.de> Subject: Re: [PATCH v2] staging: fsl-mc: add DPAA2 overview readme On 11.08.15 04:38, Stuart Yoder wrote: > > >> -----Original Message----- >> From: Alexander Graf [mailto:agraf@...e.de] >> Sent: Sunday, August 09, 2015 9:25 AM >> To: Yoder Stuart-B08248; gregkh@...uxfoundation.org; Rivera Jose-B46482; katz Itai-RM05202 >> Cc: devel@...verdev.osuosl.org; linux-kernel@...r.kernel.org; arnd@...db.de >> 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@...escale.com> >>> --- >>> -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. Awesome :). With that clarification the diagrams make much more sense. > >>> + 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. So I did guess right, just wanted to make sure you add the "one" :). > >>> + 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@...000000 | | +--+---+ >>> + +-------------------+ | | >>> + | | >>> + ================================ 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@...x" 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. I do understand what the code does, I just found the wording clumsy. Basically in a nutshell, the mc-bus driver exposes the root DPRC. > >>> + >>> + 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. That's an interesting design, thanks for the clarification. Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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