Re: Need help on Linux PCIe

[Jagan Teki]

On Wed, Dec 4, 2013 at 8:41 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
> On Tue, Dec 3, 2013 at 11:20 PM, Jagan Teki <jagannadh.teki@xxxxxxxxx> wrote:
>> Thanks for your quick response.
>> Please find my comments below.
>>
>> On Tue, Dec 3, 2013 at 11:09 PM, Bjorn Helgaas <bhelgaas@xxxxxxxxxx> wrote:
>>> On Tue, Dec 3, 2013 at 4:24 AM, Jagan Teki <jagannadh.teki@xxxxxxxxx> wrote:
>>>> Hi,
>>>>
>>>> I have few question on Linux PCIe subsystem, I am trying to understand
>>>> the PCIe on ARM platform.
>>>> 1. Compared to PCI, PCIe have an extra port functionalists/services
>>>> which is implemented drivers/pci/pcie/* is it true?
>>>
>>> Yes.
>>>
>>>> 2. PCIe root complex is same as Host controller drivers in linux drivers/host/*
>>>
>>> Yes.
>>>
>>>> 3. As individual endpoint drivers are registered to pci_core as
>>>> pci_driver_register, then what is the common call for registering
>>>> individual HC driver to pci-core?
>>>
>>> The host controller-PCI core interface is not as mature as the
>>> pci_register_driver() interface.  The basic interface is
>>> pci_scan_root_bus().  If you skim through the drivers in
>>> drivers/pci/host/* and drivers/acpi/pci_root.c, the interface to the
>>> PCI core will be fairly obvious.  And you'll learn what the existing
>>> practices are in case you need to add or modify something.
>>
>> OK.
>>
>> I understand the flow as below - please correct if am wrong.
>>
>> From low level (hw) - HC driver has a platform registration using
>> platform_driver_register() to lower layer
>> and then pci_scan_root_bus() --> pci_common_init_dev() registration to
>> upper layer as PCI - BIOS and then ends.
>
> Yes.  Sometime HC drivers use platform_driver_register(); other use
> something else depending on how the HC device is enumerated.  For
> example, drivers/acpi/pci_root.c uses something else to deal with host
> bridges in the ACPI namespace.
>
>> From upper level (app) - each endpoint driver has
>> pci_driver_register() call to PCI Core for lower level
>
> Yes.
>
>> and then the upper level registration is based on endpoint().
>
> I don't know what you mean here (I don't know of a function named
> "endpoint()").  But the driver model matches drivers to PCI functions
> based on vendor and device IDs.  A Linux "pci_dev" is what the PCI
> specs refer to as a "function."
Sorry it's typo - added ()

>
>> What is the connection here for PCI-BIOS and PCI-Core here, does these
>> are two different entities means there is no common call for these?
>> I see for ARM - "arch/arm/kernel/bios32.c" is PCI-BIOS is it correct?
>> does we have separate BIOS codes for architectures?
>
> The "pcibios_*" functions are architecture-specific things called by
> the generic PCI core.  Generally, things specified by the PCI specs
> are architecture-independent and should be in the PCI core
> (drivers/pci/*).

I have some good information to discuss from this thread.
Can you please verify this Linux PCIe subsystem stack - comment
whether my understanding is correct/not.
(I just draw this based on driver calls flow - to accommodate with in
the Linux cores)
http://jagannadhteki.blog.com/2013/12/04/linux-pcie-subsystem/

-- 
Thanks,
Jagan.
--------
Jagannadha Sutradharudu Teki,
E: jagannadh.teki@xxxxxxxxx, P: +91-9676773388
Engineer - System Software Hacker
U-boot - SPI Custodian and Zynq APSOC
Ln: http://www.linkedin.com/in/jaganteki
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