Re: [PATCH 11/14] pnv/xive: Only support crowd size of 0, 2, 4 and 16

[Nicholas Piggin]

On Wed Oct 16, 2024 at 7:13 AM AEST, Michael Kowal wrote:
> From: Glenn Miles <milesg@linux.vnet.ibm.com>
>
> XIVE crowd sizes are encoded into a 2-bit field as follows:
>   0: 0b00
>   2: 0b01
>   4: 0b10
>  16: 0b11
>
> A crowd size of 8 is not supported.

Squash this into patch 9 as a fix? xive2_pgofnext() is introduced in
patch 10, but that's not enough to worry about changing the comment.

Thanks,
Nick

>
> Signed-off-by: Glenn Miles <milesg@linux.vnet.ibm.com>
> Signed-off-by: Michael Kowal <kowal@linux.ibm.com>
> ---
>  hw/intc/xive.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
>
> diff --git a/hw/intc/xive.c b/hw/intc/xive.c
> index d5fbd9bbd8..565f0243bd 100644
> --- a/hw/intc/xive.c
> +++ b/hw/intc/xive.c
> @@ -1687,7 +1687,26 @@ static uint8_t xive_get_group_level(bool crowd, bool 
> ignore,
>      uint8_t level = 0;
>  
>      if (crowd) {
> -        level = ((ctz32(~nvp_blk) + 1) & 0b11) << 4;
> +        /* crowd level is bit position of first 0 from the right in nvp_blk 
> */
> +        level = ctz32(~nvp_blk) + 1;
> +
> +        /*
> +         * Supported crowd sizes are 2^1, 2^2, and 2^4. 2^3 is not supported.
> +         * HW will encode level 4 as the value 3.  See xive2_pgofnext().
> +         */
> +        switch (level) {
> +        case 1:
> +        case 2:
> +            break;
> +        case 4:
> +            level = 3;
> +            break;
> +        default:
> +            g_assert_not_reached();
> +        }
> +
> +        /* Crowd level bits reside in upper 2 bits of the 6 bit group level 
> */
> +        level <<= 4;
>      }
>      if (ignore) {
>          level |= (ctz32(~nvp_index) + 1) & 0b1111;