Re: [Xen-devel] [PATCH 3/3] xen/MSI: Retrieve MSI msg from cached msi_desc->msg

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Fri, Aug 15, 2014 at 11:14:37AM +0800, Yijing Wang wrote:
> We had cached the MSI msg in __write_msi_msg(),
> so we should retrieve the cached MSI msg directly,
> not to access the MSI address/data hardware registers
> again.

Is this fixing a particular problem?

Could you kindly explain to me when you do the __write_msi_msg
before doing an read_msi_msg? The order of operation in this
function is read, and then write.

> 
> Signed-off-by: Yijing Wang <wangyijing@xxxxxxxxxx>
> CC: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
> CC: xen-devel@xxxxxxxxxxxxxxxxxxxx
> ---
>  arch/x86/pci/xen.c |    2 +-
>  1 files changed, 1 insertions(+), 1 deletions(-)
> 
> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> index 4656099..7a74404 100644
> --- a/arch/x86/pci/xen.c
> +++ b/arch/x86/pci/xen.c
> @@ -228,7 +228,7 @@ static int xen_hvm_setup_msi_irqs(struct pci_dev *dev, 
> int nvec, int type)
>               return 1;
>  
>       list_for_each_entry(msidesc, &dev->msi_list, list) {
> -             read_msi_msg(msidesc, &msg);
> +             get_cached_msi_msg(msidesc, &msg);
>               pirq = MSI_ADDR_EXT_DEST_ID(msg.address_hi) |
>                       ((msg.address_lo >> MSI_ADDR_DEST_ID_SHIFT) & 0xff);
>               if (msg.data != XEN_PIRQ_MSI_DATA ||
> -- 
> 1.7.1
> 

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