Re: [PATCH v5 03/10] vpci/header: Emulate extended capability list for dom0

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, May 26, 2025 at 05:45:52PM +0800, Jiqian Chen wrote:
> Add a new function to emulate extended capability list for dom0,
> and call it in init_header(). So that it will be easy to hide a
> extended capability whose initialization fails.
> 
> As for the extended capability list of domU, just move the logic
> into above function and keep hiding it for domU.
> 
> Signed-off-by: Jiqian Chen <Jiqian.Chen@xxxxxxx>
> ---
> cc: "Roger Pau Monné" <roger.pau@xxxxxxxxxx>
> ---
> v4->v5 changes:
> * Add check: if capability list of hardware has a overlap, print warning and 
> return 0.
> 
> v3->v4 changes:
> * Add check "if ( !header )   return 0;" to avoid adding handler for
>   device that has no extended capabilities.
> 
> v2->v3 changes:
> * In vpci_init_ext_capability_list(), when domain is domU, directly return 
> after adding a handler(hiding all extended capability for domU).
> * In vpci_init_ext_capability_list(), change condition to be "while ( pos >= 
> 0x100U && ttl-- )" instead of "while ( pos && ttl-- )".
> * Add new function vpci_hw_write32, and pass it to extended capability 
> handler for dom0.
> 
> v1->v2 changes:
> new patch
> 
> Best regards,
> Jiqian Chen.
> ---
>  xen/drivers/vpci/header.c | 47 ++++++++++++++++++++++++++++++++-------
>  xen/drivers/vpci/vpci.c   |  6 +++++
>  xen/include/xen/vpci.h    |  2 ++
>  3 files changed, 47 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/drivers/vpci/header.c b/xen/drivers/vpci/header.c
> index d26cbba08ee1..4b2f761c9c24 100644
> --- a/xen/drivers/vpci/header.c
> +++ b/xen/drivers/vpci/header.c
> @@ -836,6 +836,42 @@ static int vpci_init_capability_list(struct pci_dev 
> *pdev)
>                                    PCI_STATUS_RSVDZ_MASK);
>  }
>  
> +static int vpci_init_ext_capability_list(struct pci_dev *pdev)
> +{
> +    unsigned int pos = PCI_CFG_SPACE_SIZE, ttl = 480;

I think you can drop the ttl variable, as said by Jan in a previous
review, the purpose of that counter is to detect overlaps in the PCIe
config space, but for the context here the call to vpci_add_register()
already serves that purpose by returning -EEXIST.

Thanks, Roger.