Re: [Xen-devel] Why CONFIG_XEN_PLATFORM_PCI should be equal "y" ?

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2011-11-09 at 09:43 +0000, Boris Derzhavets wrote:
> I've recently found the link :-
> 
> 
> http://xen.1045712.n5.nabble.com/PATCH-xen-remove-XEN-PLATFORM-PCI-config-option-td4833154.html
> 
> In Ubuntu 3.1 kernel configuration :-
> 
> Symbol: XEN_PLATFORM_PCI
> [=m]                                                              
>   │ Type  :
> tristate                                                                      
>    
>   │ Prompt: xen platform pci device
> driver                                                     
>   │   Defined at
> drivers/xen/Kconfig:140                                                    
>   │   Depends on: XEN [=y] && XEN_PVHVM [=y] && PCI
> [=y]                                    
>   │
> Location:                                                                     
>          
>   │     -> Device
> Drivers                                                                   
>   │       -> Xen driver support
> 
> I believe due to dependencies it should be [y].

A symbol A depending on a symbol B only means that B must be enabled but
says nothing about whether A must be enabled. If B is y this does not
imply that A must be y also.

> 
> On the other hand including xen-platform-pci.ko into initrd.img for
> Oneiric HVM will also
> enable PV-on-HVM
> 
This requires every distro to modify its initrd tools to understand when
this module is necessary (since it cannot be inferred from the explicit
dependencies), this has been a source of many bugreports. Since the code
is tiny (a few kilobytes) it was decided that it was better to build
this in. This was done in this commit, which is probably in 3.2 but not
3.1?

commit 5fbdc10395cd500d6ff844825a918c4e6f38de37
Author: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
Date:   Thu Sep 29 12:05:58 2011 +0100

    xen: remove XEN_PLATFORM_PCI config option
    
    Xen PVHVM needs xen-platform-pci, on the other hand xen-platform-pci is
    useless in any other cases.
    Therefore remove the XEN_PLATFORM_PCI config option and compile
    xen-platform-pci built-in if XEN_PVHVM is selected.
    
    Changes to v1:
    
    - remove xen-platform-pci.o and just use platform-pci.o since it is not
    externally visible anymore.
    
    Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
    Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>

Ian.


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