Re: [Qemu-ppc] [PATCH: RFC] Adding BAR0 for e500 PCI controller

[Scott Wood]

On 09/07/2012 03:08 AM, Alexander Graf wrote:
> 
> 
> On 07.09.2012, at 01:15, Scott Wood <address@hidden> wrote:
> 
>> On 09/03/2012 01:44 AM, Bhushan Bharat-R65777 wrote:
>>>
>>>
>>>> -----Original Message----- From: Wood Scott-B07421 Sent: Wednesday,
>>>> August 15, 2012 6:59 AM To: Bhushan Bharat-R65777 Cc:
>>>> address@hidden; address@hidden; address@hidden; Bhushan
>>>> Bharat- R65777 Subject: Re: [Qemu-ppc] [PATCH: RFC] Adding BAR0 for
>>>> e500 PCI controller
>>>>
>>>> On 08/14/2012 07:50 AM, Bharat Bhushan wrote:
>>>>> PCI Root complex have TYPE-1 configuration header while PCI
>>>>> endpoint have type-0 configuration header. The type-1
>>>>> configuration header have a BAR (BAR0). In Freescale PCI
>>>>> controller BAR0 is used for mapping pci address space to CCSR
>>>>> address space. This can used for 2 purposes: 1) for MSI interrupt
>>>>> generation 2) Allow CCSR registers access when configured as PCI
>>>>> endpoint, which I am not sure is a use case with QEMU-KVM
>>>> guest.
>>>>>
>>>>> What I observed is that when guest read the size of BAR0 of host 
>>>>> controller configuration header (TYPE1 header) then it always
>>>>> reads it as 0. When looking into the QEMU hw/ppce500_pci.c, I do
>>>>> not find the PCI controller device registering BAR0. I do not
>>>>> find any other controller also doing so may they do not use
>>>>> BAR0.
>>>>>
>>>>> There are two issues when BAR0 is not there (which I can think
>>>>> of): 1) There should be BAR0 emulated for PCI Root comaplex
>>>>> (TYPE1 header) and when reading the size of BAR0, it should give
>>>>> size as per real h/w.
>>>>>
>>>>> 2) Do we need this BAR0 inbound address translation? When BAR0 is
>>>>> of non-zero size then it will be configured for PCI address space
>>>>> to local address(CCSR) space translation on inbound access. The
>>>>> primary use case is for MSI interrupt generation. The device is 
>>>>> configured with a address offsets in PCI address space, which
>>>>> will be translated to MSI interrupt generation MPIC registers.
>>>>> Currently I do not understand the MSI interrupt generation
>>>>> mechanism in QEMU and also IIRC we do not use QEMU MSI interrupt
>>>>> mechanism on e500 guest machines. But this BAR0 will be used when
>>>>> using MSI on e500.
>>>>
>>>> This patch is only trying to address #1, right?  I don't see any
>>>> connection from this BAR to CCSR.
>>>>
>>>>> +    memory_region_init_io(&h->bar0, &pci_host_conf_be_ops, h, +
>>>>> "PCIHOST-bar0", 0x1000000);
>>>>
>>>> 0x01000000 is correct for e500mc-based systems, but it should be
>>>> 0x00100000 for e500v2-based systems.
>>>
>>> Scott,
>>>
>>> Currently we have a generic e500 machine which have CCSR size
>>> 0x00100000 (MPC8544_CCSRBAR_SIZE). We do not have e500mc and e500v2
>>> machines. So should we make this 0x00100000 as per generic e500
>>> machine?
>>
>> Yes, but structure it so that board code decides the size, not the PCI code.
>>
>>> Can we somehow pass this via qdev/varargs from machine emulation code
>>> (hw/ppc/e500.c) ?
>>
>> Possibly, though it may not be the best idea to express every single
>> aspect of intercomponent integration via qdev -- maybe that's best left
>> for things that are reasonably user-tweakable.  If CCSR size is user
>> tweakable, it would be somewhere other than the PCI controller.
> 
> It depends. Qdev properties are basically object constructor
> parameters. So if you were weiting C++ code and would have a
> constructor that gets the size as argument, it would end up being
> modeled as qdev property.
> 
> If however actual functionality differs, thus you would in OO speech
> create a subclass / child class, then you are better off creating a
> new device struct.
> 
> In this case, I'm not sure. They are different devices really, but
> are close enough that the differences could be expressed through qdev
> properties.

I wasn't suggesting that they be different devices.  I was suggesting
that this isn't a property of the PCI controller, but rather of some
other entity to which the PCI controller connects.  So maybe a reference
to the associated CCSR object would be a qdev parameter, but not the
size of that CCSR.

-Scott