Re: [PATCH v2] net/drivers/ieee1275/ofnet: fix incorrect netmask

[Daniel Kiper]

On Wed, Aug 24, 2022 at 01:36:37PM -0400, Robbie Harwood wrote:
> From: Masahiro Matsuya <mmatsuya@redhat.com>
>
> The netmask configured in firmware is not respected on ppc64 (big
> endian).  When 255.255.252.0 is set as netmask in firmware, the
> following is the value of bootpath string in
> grub_ieee1275_parse_bootpath():
>
> /vdevice/l-lan@30000002:speed=auto,duplex=auto,192.168.88.10,,192.168.89.113,192.168.88.1,5,5,255.255.252.0,512
>
> The netmask in this bootpath is no problem, since it's a value specified
> in firmware.  But the value of 'subnet_mask.ipv4' was set with
> 0xfffffc00, and __builtin_ctz (~grub_le_to_cpu32 (subnet_mask.ipv4))
> returned 16 (not 22).  As a result, 16 was used for netmask wrongly:
>
> 1111 1111 1111 1111 1111 1100 0000 0000 # subnet_mask.ipv4 (=0xfffffc00)
> 0000 0000 1111 1100 1111 1111 1111 1111 # grub_le_to_cpu32 (subnet_mask.ipv4)
> 1111 1111 0000 0011 0000 0000 0000 0000 # ~grub_le_to_cpu32 (subnet_mask.ipv4)
>
> and the count of zero with __builtin_ctz can be 16.  This patch changes
> it as below:
>
> 1111 1111 1111 1111 1111 1100 0000 0000 # subnet_mask.ipv4 (=0xfffffc00)
> 0000 0000 1111 1100 1111 1111 1111 1111 # grub_le_to_cpu32 (subnet_mask.ipv4)
> 1111 1111 1111 1111 1111 1100 0000 0000 # grub_be_to_cpu32 (subnet_mask.ipv4)
> 0000 0000 0000 0000 0000 0011 1111 1111 # ~grub_be_to_cpu32 (subnet_mask.ipv4)
>
> The count of zero with __builtin_clz can be 22.  (clz counts the number
> of one bits preceding the most significant zero bit)
>
> Signed-off-by: Masahiro Matsuya <mmatsuya@redhat.com>
> Signed-off-by: Robbie Harwood <rharwood@redhat.com>

Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

Daniel