Re: [dpdk-dev] [PATCH v2] dmadev: introduce DMA device library

[Jerin Jacob <jerinjacobk@gmail.com>]

On Sun, Jul 11, 2021 at 2:59 PM Chengwen Feng <fengchengwen@huawei.com> 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>
> ---
> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Enqueue a fill operation onto the virtual DMA channel.
> + *
> + * This queues up a fill operation to be performed by hardware, but does not
> + * trigger hardware to begin that operation.
> + *
> + * @param dev_id
> + *   The identifier of the device.
> + * @param vchan
> + *   The identifier of virtual DMA channel.
> + * @param pattern
> + *   The pattern to populate the destination buffer with.
> + * @param dst
> + *   The address of the destination buffer.
> + * @param length
> + *   The length of the destination buffer.
> + * @param flags
> + *   An flags for this operation.
> + *
> + * @return
> + *   - 0..UINT16_MAX: index of enqueued copy job.

fill job

> + *   - <0: Error code returned by the driver copy function.
> + */
> +__rte_experimental
> +static inline int
> +rte_dmadev_fill(uint16_t dev_id, uint16_t vchan, uint64_t pattern,
> +               rte_iova_t dst, uint32_t length, uint64_t flags)
> +{
> +       struct rte_dmadev *dev = &rte_dmadevices[dev_id];
> +#ifdef RTE_DMADEV_DEBUG
> +       RTE_DMADEV_VALID_DEV_ID_OR_ERR_RET(dev_id, -EINVAL);
> +       RTE_FUNC_PTR_OR_ERR_RET(*dev->fill, -ENOTSUP);
> +       if (vchan >= dev->data->dev_conf.max_vchans) {
> +               RTE_DMADEV_LOG(ERR, "Invalid vchan %d\n", vchan);
> +               return -EINVAL;
> +       }
> +#endif
> +       return (*dev->fill)(dev, vchan, pattern, dst, length, flags);
> +}
> +

> +/**
> + * @warning
> + * @b EXPERIMENTAL: this API may change without prior notice.
> + *
> + * Returns the number of operations that have been successfully completed.
> + *
> + * @param dev_id
> + *   The identifier of the device.
> + * @param vchan
> + *   The identifier of virtual DMA channel.
> + * @param nb_cpls
> + *   The maximum number of completed operations that can be processed.
> + * @param[out] last_idx
> + *   The last completed operation's index.
> + *   If not required, NULL can be passed in.

This means the driver will be tracking the last index.

Is that mean, the application needs to call this API periodically to
consume the completion slot.
I.e up to 64K (UINT16_MAX)  outstanding jobs are possible. If the
application fails to call this
>64K outstand job then the subsequence enqueue will fail.

If so, we need to document this.

One of the concerns of keeping UINT16_MAX as the limit is the
completion memory will always not in cache.
On the other hand, if we make this size programmable. it may introduce
complexity in the application.

Thoughts?


> + * @param[out] has_error
> + *   Indicates if there are transfer error.
> + *   If not required, NULL can be passed in.
> + *
> + * @return
> + *   The number of operations that successfully completed.
> + */
> +__rte_experimental
> +static inline uint16_t
> +rte_dmadev_completed(uint16_t dev_id, uint16_t vchan, const uint16_t nb_cpls,
> +                    uint16_t *last_idx, bool *has_error)
> +{
> +       struct rte_dmadev *dev = &rte_dmadevices[dev_id];
> +       uint16_t idx;
> +       bool err;
> +
> +#ifdef RTE_DMADEV_DEBUG
> +       RTE_DMADEV_VALID_DEV_ID_OR_ERR_RET(dev_id, -EINVAL);
> +       RTE_FUNC_PTR_OR_ERR_RET(*dev->completed, -ENOTSUP);
> +       if (vchan >= dev->data->dev_conf.max_vchans) {
> +               RTE_DMADEV_LOG(ERR, "Invalid vchan %d\n", vchan);
> +               return -EINVAL;
> +       }
> +       if (nb_cpls == 0) {
> +               RTE_DMADEV_LOG(ERR, "Invalid nb_cpls\n");
> +               return -EINVAL;
> +       }
> +#endif
> +
> +       /* Ensure the pointer values are non-null to simplify drivers.
> +        * In most cases these should be compile time evaluated, since this is
> +        * an inline function.
> +        * - If NULL is explicitly passed as parameter, then compiler knows the
> +        *   value is NULL
> +        * - If address of local variable is passed as parameter, then compiler
> +        *   can know it's non-NULL.
> +        */
> +       if (last_idx == NULL)
> +               last_idx = &idx;
> +       if (has_error == NULL)
> +               has_error = &err;
> +
> +       *has_error = false;
> +       return (*dev->completed)(dev, vchan, nb_cpls, last_idx, has_error);
> +}