Re: [dpdk-dev] [PATCH v3] dmadev: introduce DMA device library

[fengchengwen <fengchengwen@huawei.com>]

Thank you for your valuable comments, and I think we've taken a big step forward.

@andrew Could you provide the copyright line so that I can add it to relevant file.

@burce, jerin  Some unmodified review comments are returned here:

1.
COMMENT: We allow up to 100 characters per line for DPDK code, so these don't need
to be wrapped so aggressively.

REPLY: Our CI still has 80 characters limit, and I review most framework still comply.

2.
COMMENT: > +#define RTE_DMA_MEM_TO_MEM     (1ull << 0)
RTE_DMA_DIRECTION_...

REPLY: add the 'DIRECTION' may the macro too long, I prefer keep it simple.

3.
COMMENT: > +rte_dmadev_vchan_release(uint16_t dev_id, uint16_t vchan);
We are not making release as pubic API in other device class. See ethdev spec.
bbdev/eventdev/rawdev

REPLY: because ethdev's queue is hard-queue, and here is the software defined channels,
I think release is OK, BTW: bbdev/eventdev also have release ops.

4.
COMMENT:> +       uint64_t reserved[4]; /**< Reserved for future fields */
> +};
Please add the capability for each counter in info structure as one
device may support all
the counters.

REPLY: This is a statistics function. If this function is not supported, then do not need
to implement the stats ops function. Also could to set the unimplemented ones to zero.

5.
COMMENT: > +#endif
> +       return (*dev->fill)(dev, vchan, pattern, dst, length, flags);
Instead of every driver set the NOP function, In the common code, If
the CAPA is not set,
common code can set NOP function for this with <0 return value.

REPLY: I don't think it's a good idea to judge in IO path, it's application duty to ensure
don't call API which driver not supported (which could get from capabilities).

6.
COMMENT: > +rte_dmadev_completed_fails(uint16_t dev_id, uint16_t vchan,
> +                          const uint16_t nb_status, uint32_t *status,
uint32_t -> enum rte_dma_status_code

REPLY：I'm still evaluating this. It takes a long time for the driver to perform error code
conversion in this API. Do we need to provide an error code conversion function alone ?

7.
COMMENT: > +typedef int (*dmadev_info_get_t)(struct rte_dmadev *dev,
> +                                struct rte_dmadev_info *dev_info);
Please change to rte_dmadev_info_get_t to avoid conflict due to namespace issue
as this header is exported.

REPLY: I prefer not add 'rte_' prefix, it make the define too long.

8.
COMMENT: > + *        - rte_dmadev_completed_fails()
> + *            - return the number of operation requests failed to complete.
Please rename this to "completed_status" to allow the return of information
other than just errors. As I suggested before, I think this should also be
usable as a slower version of "completed" even in the case where there are
no errors, in that it returns status information for each and every job
rather than just returning as soon as it hits a failure.

REPLY: well, I think it maybe confuse (current OK/FAIL API is easy to understand.),
and we can build the slow path function on the two API.

9.
COMMENT: > +#define RTE_DMA_DEV_CAPA_MEM_TO_MEM	(1ull << 0)
> +/**< DMA device support mem-to-mem transfer.
Do we need this? Can we assume that any device appearing as a dmadev can
do mem-to-mem copies, and drop the capability for mem-to-mem and the
capability for copying?
also for RTE_DMA_DEV_CAPA_OPS_COPY

REPLY: yes, I insist on adding this for the sake of conceptual integrity.
For ioat driver just make a statement.

10.
COMMENT: > +	uint16_t nb_vchans; /**< Number of virtual DMA channel configured */
> +};
Let's add rte_dmadev_conf struct into this to return the configuration
settings.

REPLY: If we add rte_dmadev_conf in, it may break ABI when rte_dmadev_conf add fields.


[snip]

On 2021/7/13 20:27, Chengwen Feng wrote:
> This patch introduce 'dmadevice' which is a generic type of DMA
> device.
> 
> The APIs of dmadev library exposes some generic operations which can
> enable configuration and I/O with the DMA devices.
> 
> Signed-off-by: Chengwen Feng <fengchengwen@huawei.com>
> ---
> v3:
> * rm reset and fill_sg ops.
> * rm MT-safe capabilities.
> * add submit flag.
> * redefine rte_dma_sg to implement asymmetric copy.
> * delete some reserved field for future use.
> * rearrangement rte_dmadev/rte_dmadev_data struct.
> * refresh rte_dmadev.h copyright.
> * update vchan setup parameter.
> * modified some inappropriate descriptions.
> * arrange version.map alphabetically.
> * other minor modifications from review comment.
> ---
>  MAINTAINERS                  |   4 +
>  config/rte_config.h          |   3 +
>  lib/dmadev/meson.build       |   7 +
>  lib/dmadev/rte_dmadev.c      | 561 +++++++++++++++++++++++++
>  lib/dmadev/rte_dmadev.h      | 968 +++++++++++++++++++++++++++++++++++++++++++
>  lib/dmadev/rte_dmadev_core.h | 161 +++++++
>  lib/dmadev/rte_dmadev_pmd.h  |  72 ++++
>  lib/dmadev/version.map       |  37 ++
>  lib/meson.build              |   1 +