Date:	Fri, 17 Jul 2015 20:16:49 +0000
From:	Johannes Thumshirn <jthumshirn@...e.de>
To:	Randy Dunlap <rdunlap@...radead.org>
Cc:	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] Documentation: Add MCB documentation

Zitat von Randy Dunlap <rdunlap@...radead.org>:

> 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?
>

MEN is a company building this hardware. I guess this was a bit more  
obvious when my emails ended on @men.de. Let me see how I can get this  
information in there.

>> +
>> +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".

Now that you write it, I must admit it sounds more correct with "a".

>
>> +   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
>

Thanks for looking at it Randy.

For the remaining issues, do you want a v3 or a patch to the version  
in the docs tree Jon?

Johannes

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