Re: [PATCH v9 1/2] xen/vpci: header: status register handler

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

On Fri, Dec 01, 2023 at 10:45:49AM -0500, Stewart Hildebrand wrote:
> Introduce a handler for the PCI status register, with ability to mask
> the capabilities bit. The status register contains RsvdZ bits,
> read-only bits, and write-1-to-clear bits. Additionally, we use RsvdP to
> mask the capabilities bit. Introduce bitmasks to handle these in vPCI.
> If a bit in the bitmask is set, then the special meaning applies:
> 
>   ro_mask: read normal, guest write ignore (preserve on write to hardware)
>   rw1c_mask: read normal, write 1 to clear
>   rsvdp_mask: read as zero, guest write ignore (preserve on write to hardware)
>   rsvdz_mask: read as zero, guest write ignore (write zero to hardware)
> 
> The RO/RW1C/RsvdP/RsvdZ naming and definitions were borrowed from the
> PCI Express Base 6.1 specification. RsvdP/RsvdZ bits help Xen enforce
> our view of the world. Xen preserves the value of read-only bits on
> write to hardware, discarding the guests write value. This is done in
> case hardware wrongly implements R/O bits as R/W.
> 
> The mask_cap_list flag will be set in a follow-on patch.
                                                    ^ s/patch/change/

> 
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>

Reviewed-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>

Thanks, Roger.