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

[Cornelia Huck <cohuck@redhat.com>]

On Tue,  5 Sep 2017 13:16:44 +0200
Halil Pasic <pasic@linux.vnet.ibm.com> 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 <pasic@linux.vnet.ibm.com>
> ---
>  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'?

> +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 ;)

[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?

> +
>  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;
>      }
>  }
>