Message-ID: <55A947C4.6020606@infradead.org>
Date:	Fri, 17 Jul 2015 11:21:56 -0700
From:	Randy Dunlap <rdunlap@...radead.org>
To:	Johannes Thumshirn <jthumshirn@...e.de>,
	Jonathan Corbet <corbet@....net>
CC:	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Documentation: Add MCB documentation

On 07/17/15 03:23, Johannes Thumshirn wrote:
> Add basic introductory documentation for the MEN Chameleon Bus.
> 
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> ---
> 
> So this time I totally forgot about it..
> 
>  Changes from v1:
>  - Renamed MCB.txt to men-chameleon-bus.txt
>  - Added entry to MAINTAINERS file
> 
>  Documentation/men-chameleon-bus.txt | 162 ++++++++++++++++++++++++++++++++++++
>  MAINTAINERS                         |   1 +
>  2 files changed, 163 insertions(+)
>  create mode 100644 Documentation/men-chameleon-bus.txt
> 
> diff --git a/Documentation/men-chameleon-bus.txt b/Documentation/men-chameleon-bus.txt
> new file mode 100644
> index 0000000..6d7bdb5
> --- /dev/null
> +++ b/Documentation/men-chameleon-bus.txt
> @@ -0,0 +1,162 @@
> +                               MEN Chameleon Bus
> +                               =================
> +
> +Table of Contents
> +=================
> +1 Introduction
> +    1.1 Scope of this Document
> +    1.2 Limitations of the current implementation
> +2 Architecture
> +    2.1 MEN Chameleon Bus
> +    2.2 Carrier Devices
> +    2.3 Parser
> +3 Resource handling
> +    3.1 Memory Resources
> +    3.2 IRQs
> +4 Writing a MCB driver

             an

> +    4.1 The driver structure
> +    4.2 Probing and attaching
> +    4.3 Initializing the driver
> +
> +
> +1 Introduction
> +===============
> +  This document describes the architecture and implementation of the MEN
> +  Chameleon Bus (called MCB throughout this document).

What does "MEN" mean?

> +
> +1.1 Scope of this Document
> +---------------------------
> +  This document is intended to be a short overview of the current
> +  implementation and does by no means describe to complete possibilities of MCB

                                                  the

> +  based devices.
> +
> +1.2 Limitations of the current implementation
> +----------------------------------------------
> +  The current implementation is limited to PCI and PCIe based carrier devices
> +  that only use a single memory resource and share the PCI legacy IRQ.  Not
> +  implemented are:
> +  - Multi-resource MCB devices like the VME Controller or M-Module carrier.
> +  - MCB devices that need another MCB device, like SRAM for a DMA Controller's
> +    buffer descriptors or a video controller's video memory.
> +  - A per-carrier IRQ domain for carrier devices that have one (or more) IRQs
> +    per MCB device like PCIe based carriers with MSI or MSI-X support.
> +
> +2 Architecture
> +===============
> +  MCB is divided in 3 functional blocks:

                    into

> +  - The MEN Chameleon Bus itself,
> +  - drivers for MCB Carrier Devices and
> +  - the parser for the Chameleon table.
> +
> +2.1 MEN Chameleon Bus
> +----------------------
> +   The MEN Chameleon Bus is an artificial bus system that attaches to an MEN

I would write "to a MEN" instead of "to an MEN", but I guess it depends on
whether one is reading it as a word (men) or 3 letters (M E N).  I read it as
a word, so it's "to a MEN".

> +   Chameleon FPGA device. These devices are multi-function devices implemented
> +   in a single FPGA and usually attached via some sort of PCI or PCIe link. Each
> +   FPGA contains a header section describing the content of the FPGA. The header
> +   lists the device id, PCI BAR, offset from the beginning of the PCI BAR, size
> +   in the FPGA, interrupt number and some other properties currently not handled
> +   by the MCB implementation.
> +
> +2.2 Carrier Devices
> +--------------------
> +   A carrier device is just an abstraction for the real world physical bus the
> +   chameleon FPGA is attached to. Some IP Core drivers may need to interact with
> +   properties of the carrier device (like querying the IRQ number of a PCI
> +   device). To provide abstraction from the real hardware bus, an MCB carrier
> +   device provides callback methods to translate the driver's MCB function calls
> +   to hardware related function calls. For example a carrier device may
> +   implement the get_irq() method which can be translate into a hardware bus

                                                  translated

> +   query for the IRQ number the device should use.
> +
> +2.3 Parser
> +-----------
> +   The parser reads the 1st 512 bytes of a chameleon device and parses the

                           first

Why sometimes capitalize Chameleon and sometimes not?  What criteria do you
use to make that choice?

> +   chameleon table. Currently the parser only supports the Chameleon v2 variant
> +   of the chameleon table but can easily be adopted to support an older or
> +   possible future variant. While parsing the table's entries new MCB devices
> +   are allocated and their resources are assigned according to the resource
> +   assignment in the chameleon table. After resource assignment is finished, the
> +   MCB devices are registered at the MCB and thus at the driver core of the
> +   Linux kernel.
> +
> +3 Resource handling
> +====================
> +  The current implementation assigns exactly one memory and one IRQ resource
> +  per MCB device. But this is likely going to change in the future.
> +
> +3.1 Memory Resources
> +---------------------
> +   Each MCB device has exactly one memory resource, which can be requested from
> +   the MCB bus. This memory resource is the physical address of the MCB device
> +   inside the carrier and is intended to be passed to ioremap() and friends. It
> +   is already requested from the kernel by calling request_mem_region().
> +
> +3.2 IRQs
> +---------
> +   Each MCB device has exactly one IRQ resource, which can be requested from the
> +   MCB bus. If a carrier device driver implements the ->get_irq() callback
> +   method, the IRQ number assigned by the carrier device will be returned,
> +   otherwise the IRQ number inside the chameleon table will be returned. This
> +   number is suitable to be passed to request_irq().
> +
> +4 Writing a MCB driver

             an

> +=======================
> +
> +4.1 The driver structure
> +-------------------------
> +    Each MCB driver has a structure to identify the device driver as well as
> +    device ids which identify the IP Core inside the FPGA. The driver structure
> +    also contaings callback methods which get executed on driver probe and

            contains

> +    removal from the system.
> +
> +
> +  static const struct mcb_device_id foo_ids[] = {
> +          { .device = 0x123 },
> +          { }
> +  };
> +  MODULE_DEVICE_TABLE(mcb, foo_ids);
> +
> +  static struct mcb_driver foo_driver = {
> +          driver = {
> +                  .name = "foo-bar",
> +                  .owner = THIS_MODULE,
> +          },
> +          .probe = foo_probe,
> +          .remove = foo_remove,
> +          .id_table = foo_ids,
> +  };
> +
> +4.2 Probing and attaching
> +--------------------------
> +   When a driver is loaded and the MCB devices it services are found, the MCB
> +   core will call the driver's probe callback method. When the driver is removed
> +   from the system, the MCB core will call the driver's remove callback method.
> +
> +
> +  static init foo_probe(struct mcb_device *mdev, const struct mcb_device_id *id);
> +  static void foo_remove(struct mcb_device *mdev);
> +
> +4.3 Initializing the driver
> +----------------------------
> +   When the kernel is booted or your foo driver module is inserted, you have to
> +   perform driver initialization. Usually it is enough to register your driver
> +   module at the MCB core.
> +
> +
> +  static int __init foo_init(void)
> +  {
> +          return mcb_register_driver(&foo_driver);
> +  }
> +  module_init(foo_init);
> +
> +  static void __exit foo_exit(void)
> +  {
> +          mcb_unregister_driver(&foo_driver);
> +  }
> +  module_exit(foo_exit);
> +
> +   The module_mcb_driver() macro can be used to reduce the above code.
> +
> +
> +  module_mcb_driver(foo_driver);


-- 
~Randy
--
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