Re: [PATCH v5 04/12] pc-bios: s390x: Get rid of magic offsets into the lowcore

[Thomas Huth <thuth@redhat.com>]

On 24/06/2020 09.52, Janosch Frank wrote:
> If we have a lowcore struct that has members for offsets that we want
> to touch, why not use it?
> 
> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> ---
>   pc-bios/s390-ccw/cio.h  | 17 +++++++++++------
>   pc-bios/s390-ccw/main.c |  8 +++-----
>   2 files changed, 14 insertions(+), 11 deletions(-)
> 
> diff --git a/pc-bios/s390-ccw/cio.h b/pc-bios/s390-ccw/cio.h
> index aaa432dedd..1e5d4e92e1 100644
> --- a/pc-bios/s390-ccw/cio.h
> +++ b/pc-bios/s390-ccw/cio.h
> @@ -122,12 +122,17 @@ typedef struct schib {
>   } __attribute__ ((packed, aligned(4))) Schib;
>   
>   typedef struct subchannel_id {
> -        __u32 cssid:8;
> -        __u32:4;
> -        __u32 m:1;
> -        __u32 ssid:2;
> -        __u32 one:1;
> -        __u32 sch_no:16;
> +    union {
> +        struct {
> +            __u16 cssid:8;
> +            __u16 reserved:4;
> +            __u16 m:1;
> +            __u16 ssid:2;
> +            __u16 one:1;
> +        };
> +        __u16 sch_id;
> +    };
> +    __u16 sch_no;
>   } __attribute__ ((packed, aligned(4))) SubChannelId;
>   
>   struct chsc_header {
> diff --git a/pc-bios/s390-ccw/main.c b/pc-bios/s390-ccw/main.c
> index 4e65b411e1..8b912454c9 100644
> --- a/pc-bios/s390-ccw/main.c
> +++ b/pc-bios/s390-ccw/main.c
> @@ -36,11 +36,9 @@ LowCore *lowcore; /* Yes, this *is* a pointer to address 0 */
>    */
>   void write_subsystem_identification(void)
>   {
> -    SubChannelId *schid = (SubChannelId *) 184;
> -    uint32_t *zeroes = (uint32_t *) 188;
> -
> -    *schid = blk_schid;
> -    *zeroes = 0;
> +    lowcore->subchannel_id = blk_schid.sch_id;
> +    lowcore->subchannel_nr = blk_schid.sch_no;
> +    lowcore->io_int_parm = 0;
>   }

Ok, I have to admit that I had to read it multiple times (maybe not 
enough coffee the last time), but it looks fine to me now.

Reviewed-by: Thomas Huth <thuth@redhat.com>