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List:       qemu-s390x
Subject:    Re: [PATCH v3 4/9] pc-bios: s390x: Get rid of magic offsets into the lowcore
From:       Janosch Frank <frankja () linux ! ibm ! com>
Date:       2020-05-27 11:23:17
Message-ID: d02ec3bf-e74e-ea55-d05c-c701acff2673 () linux ! ibm ! com
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On 5/27/20 10:50 AM, Christian Borntraeger wrote:
> 
> 
> On 27.05.20 09:49, 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;
>>  }
>>  
>>  void write_iplb_location(void)
> 
> As an alternative, why not change the definition of Lowcore and replace both 16bit
> fields lowcore->subchannel_id and lowcore->subchannel_nr with SubChannelID.
> You can then simply assign lowcore->schid= blk_schid;
> 
> ?
> 
I think Pierre voted against that in the internal review if I remember
correctly.


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