Re: [Qemu-devel] [PATCH 4/5] s390x/css: support ccw IDA

[Halil Pasic]

On 09/06/2017 03:10 PM, Cornelia Huck wrote:
> On Tue,  5 Sep 2017 13:16:44 +0200
> Halil Pasic <address@hidden> wrote:
> 
>> Let's add indirect data addressing support for our virtual channel
>> subsystem. This implementation does no prefetching, but steps
>> trough the idal as we go.
>>
>> Signed-off-by: Halil Pasic <address@hidden>
>> ---
>>  hw/s390x/css.c | 110 
>> ++++++++++++++++++++++++++++++++++++++++++++++++++++++++-
>>  1 file changed, 109 insertions(+), 1 deletion(-)
>>
>> diff --git a/hw/s390x/css.c b/hw/s390x/css.c
>> index c1bc9944e6..9d8f9fd7ea 100644
>> --- a/hw/s390x/css.c
>> +++ b/hw/s390x/css.c
>> @@ -819,6 +819,114 @@ incr:
>>      return 0;
>>  }
>>  
>> +/* retuns values between 1 and bs, where bs is a power of 2 */
> 
> 'bs' is 'block size'?

Yes.

> 
>> +static inline uint16_t ida_continuous_left(hwaddr cda, uint64_t bs)
>> +{
>> +    return bs - (cda & (bs - 1));
>> +}
>> +
>> +static inline uint64_t ccw_ida_block_size(uint8_t flags)
>> +{
>> +    return 1ULL << (((flags ^ CDS_F_C64) & (CDS_F_C64 | CDS_F_I2K)) ? 11 : 
>> 12);
>> +}
>> +
>> +static inline int ida_read_next_idaw(CcwDataStream *cds)
>> +{
>> +    union {uint64_t fmt2; uint32_t fmt1; } idaw;
>> +    bool is_fmt2 = cds->flags & CDS_F_C64;
>> +    int ret;
>> +    hwaddr idaw_addr;
>> +
>> +    if (is_fmt2) {
>> +        idaw_addr = cds->cda_orig + sizeof(idaw.fmt2) * cds->at_idaw;
>> +        if (idaw_addr & 0x07) {
>> +            return -EINVAL; /* chanel program check */
> 
> How fashionable ;)
> 

Learned something new.

> [s/chanel/channel/ :D]
> 
>> +        }
>> +        ret = address_space_rw(&address_space_memory, idaw_addr,
>> +                               MEMTXATTRS_UNSPECIFIED, (void *) &idaw.fmt2,
>> +                               sizeof(idaw.fmt2), false);
>> +        cds->cda = be64_to_cpu(idaw.fmt2);
>> +    } else {
>> +        idaw_addr = cds->cda_orig + sizeof(idaw.fmt1) * cds->at_idaw;
>> +        if (idaw_addr & 0x03) {
>> +            return -EINVAL; /* chanel program check */
>> +
>> +        }
>> +        ret = address_space_rw(&address_space_memory, idaw_addr,
>> +                               MEMTXATTRS_UNSPECIFIED, (void *) &idaw.fmt1,
>> +                               sizeof(idaw.fmt1), false);
>> +        cds->cda = be64_to_cpu(idaw.fmt1);
>> +    }
>> +    ++(cds->at_idaw);
>> +    if (ret != MEMTX_OK) {
>> +        /* assume inaccessible address */
>> +        return -EINVAL; /* chanel program check */
>> +
>> +    }
>> +    return 0;
>> +}
>> +
>> +static int ccw_dstream_rw_ida(CcwDataStream *cds, void *buff, int len,
>> +                              CcwDataStreamOp op)
>> +{
>> +    uint64_t bs = ccw_ida_block_size(cds->flags);
>> +    int ret = 0;
>> +    uint16_t cont_left, iter_len;
>> +
>> +    ret = cds_check_len(cds, len);
>> +    if (ret <= 0) {
>> +        return ret;
>> +    }
>> +    if (!cds->at_idaw) {
>> +        /* read first idaw */
>> +        ret = ida_read_next_idaw(cds);
>> +        if (ret) {
>> +            goto err;
>> +        }
>> +        cont_left = ida_continuous_left(cds->cda, bs);
>> +    } else {
>> +        cont_left = ida_continuous_left(cds->cda, bs);
>> +        if (cont_left == bs) {
>> +            ret = ida_read_next_idaw(cds);
>> +            if (ret) {
>> +                goto err;
>> +            }
>> +            if (cds->cda & (bs - 1)) {
>> +                ret = -EINVAL; /* chanel program check */
>> +                goto err;
>> +            }
>> +        }
>> +    }
>> +do_iter_len:
>> +    iter_len = MIN(len, cont_left);
>> +    if (op == CDS_OP_A) {
>> +        goto incr;
>> +    }
>> +    ret = address_space_rw(&address_space_memory, cds->cda,
>> +                           MEMTXATTRS_UNSPECIFIED, buff, iter_len, op);
>> +    if (ret != MEMTX_OK) {
>> +        /* assume inaccessible address */
>> +        ret = -EINVAL; /* chanel program check */
>> +        goto err;
>> +    }
>> +incr:
>> +    cds->at_byte += iter_len;
>> +    cds->cda += iter_len;
>> +    len -= iter_len;
>> +    if (len) {
>> +        ret = ida_read_next_idaw(cds);
>> +        if (ret) {
>> +            goto err;
>> +        }
>> +        cont_left = bs;
>> +        goto do_iter_len;
>> +    }
>> +    return ret;
>> +err:
>> +    cds->flags |= CDS_F_STREAM_BROKEN;
>> +    return ret;
>> +}
> 
> I'm not so happy about the many gotos (excepting the err ones). Any
> chance to get around these?
> 
Certainly possible:

static int ccw_dstream_rw_ida(CcwDataStream *cds, void *buff, int len,          
                              CcwDataStreamOp op)                               
{                                                                               
    uint64_t bs = ccw_ida_block_size(cds->flags);                               
    int ret = 0;                                                                
    uint16_t cont_left, iter_len;                                               
                                                                                
    ret = cds_check_len(cds, len);                                              
    if (ret <= 0) {                                                             
        return ret;                                                             
    }                                                                           
    if (!cds->at_idaw) {                                                        
        /* read first idaw */                                                   
        ret = ida_read_next_idaw(cds);                                          
        if (ret) {                                                              
            goto err;                                                           
        }                                                                       
        cont_left = ida_continuous_left(cds->cda, bs);                          
    } else {                                                                    
        cont_left = ida_continuous_left(cds->cda, bs);                          
        if (cont_left == bs) {                                                  
            ret = ida_read_next_idaw(cds);                                      
            if (ret) {                                                          
                goto err;                                                       
            }                                                                   
            if (cds->cda & (bs - 1)) {                                          
                ret = -EINVAL; /* channel program check */                      
                goto err;                                                       
            }                                                                   
        }                                                                       
    }                                                                           
    do {                                                                        
        iter_len = MIN(len, cont_left);                                         
        if (op != CDS_OP_A) {                                                   
            ret = address_space_rw(&address_space_memory, cds->cda,             
                                   MEMTXATTRS_UNSPECIFIED, buff, iter_len, op); 
            if (ret != MEMTX_OK) {                                              
                /* assume inaccessible address */                               
                ret = -EINVAL; /* channel program check */                      
                goto err;                                                       
            }                                                                   
        }                                                                       
        cds->at_byte += iter_len;                                               
        cds->cda += iter_len;                                                   
        len -= iter_len;                                                        
        if (!len) {                                                             
            break;                                                              
        }                                                                       
        ret = ida_read_next_idaw(cds);                                          
        if (ret) {                                                              
            goto err;                                                           
        }                                                                       
        cont_left = bs;                                                         
    } while (true);                                                             
    return ret;                                                                 
err:                                                                            
    cds->flags |= CDS_F_STREAM_BROKEN;                                          
    return ret;                                                                 
}

My idea was decrease indentation level and at the same time make
labels tell us something about the purpose of code pieces. Which
one do you prefer?

Sorry I've forgot about this comment. I would not have negotiated
v2 before clarifying this.

Halil

>> +
>>  void ccw_dstream_init(CcwDataStream *cds, CCW1 const *ccw, ORB const *orb)
>>  {
>>      /*
>> @@ -835,7 +943,7 @@ void ccw_dstream_init(CcwDataStream *cds, CCW1 const 
>> *ccw, ORB const *orb)
>>      if (!(cds->flags & CDS_F_IDA)) {
>>          cds->op_handler = ccw_dstream_rw_noflags;
>>      } else {
>> -        assert(false);
>> +        cds->op_handler = ccw_dstream_rw_ida;
>>      }
>>  }
>>  
> 
>