Hi Laurent,
On 23/01/2020 4.29, Laurent Pinchart wrote:
> The new interleaved cyclic transaction type combines interleaved and
> cycle transactions. It is designed for DMA engines that back display
> controllers, where the same 2D frame needs to be output to the display
> until a new frame is available.
>
> Suggested-by: Vinod Koul <vkoul@xxxxxxxxxx>
> Signed-off-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> ---
> drivers/dma/dmaengine.c | 8 +++++++-
> include/linux/dmaengine.h | 18 ++++++++++++++++++
> 2 files changed, 25 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 03ac4b96117c..4ffb98a47f31 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -981,7 +981,13 @@ int dma_async_device_register(struct dma_device *device)
> "DMA_INTERLEAVE");
> return -EIO;
> }
> -
> + if (dma_has_cap(DMA_INTERLEAVE_CYCLIC, device->cap_mask) &&
> + !device->device_prep_interleaved_cyclic) {
> + dev_err(device->dev,
> + "Device claims capability %s, but op is not defined\n",
> + "DMA_INTERLEAVE_CYCLIC");
> + return -EIO;
> + }
>
> if (!device->device_tx_status) {
> dev_err(device->dev, "Device tx_status is not defined\n");
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 8fcdee1c0cf9..e9af3bf835cb 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -61,6 +61,7 @@ enum dma_transaction_type {
> DMA_SLAVE,
> DMA_CYCLIC,
> DMA_INTERLEAVE,
> + DMA_INTERLEAVE_CYCLIC,
> /* last transaction type for creation of the capabilities mask */
> DMA_TX_TYPE_END,
> };
> @@ -701,6 +702,10 @@ struct dma_filter {
> * The function takes a buffer of size buf_len. The callback function will
> * be called after period_len bytes have been transferred.
> * @device_prep_interleaved_dma: Transfer expression in a generic way.
> + * @device_prep_interleaved_cyclic: prepares an interleaved cyclic transfer.
> + * This is similar to @device_prep_interleaved_dma, but the transfer is
> + * repeated until a new transfer is issued. This transfer type is meant
> + * for display.
I think capture (camera) is another potential beneficiary of this.
So you don't need to terminate the running interleaved_cyclic and start
a new one, but prepare and issue a new one, which would
terminate/replace the currently running cyclic interleaved DMA?
Can you also update the documentation at
Documentation/driver-api/dmaengine/client.rst
One more thing might be good to clarify for the interleaved_cyclic:
What is expected when DMA_PREP_INTERRUPT is set in the flags? The
client's callback is called for each completion of
dma_interleaved_template, right?
- Péter
> * @device_prep_dma_imm_data: DMA's 8 byte immediate data to the dst address
> * @device_config: Pushes a new configuration to a channel, return 0 or an error
> * code
> @@ -785,6 +790,9 @@ struct dma_device {
> struct dma_async_tx_descriptor *(*device_prep_interleaved_dma)(
> struct dma_chan *chan, struct dma_interleaved_template *xt,
> unsigned long flags);
> + struct dma_async_tx_descriptor *(*device_prep_interleaved_cyclic)(
> + struct dma_chan *chan, struct dma_interleaved_template *xt,
> + unsigned long flags);
> struct dma_async_tx_descriptor *(*device_prep_dma_imm_data)(
> struct dma_chan *chan, dma_addr_t dst, u64 data,
> unsigned long flags);
> @@ -880,6 +888,16 @@ static inline struct dma_async_tx_descriptor *dmaengine_prep_interleaved_dma(
> return chan->device->device_prep_interleaved_dma(chan, xt, flags);
> }
>
> +static inline struct dma_async_tx_descriptor *dmaengine_prep_interleaved_cyclic(
> + struct dma_chan *chan, struct dma_interleaved_template *xt,
> + unsigned long flags)
> +{
> + if (!chan || !chan->device || !chan->device->device_prep_interleaved_cyclic)
> + return NULL;
> +
> + return chan->device->device_prep_interleaved_cyclic(chan, xt, flags);
> +}
> +
> static inline struct dma_async_tx_descriptor *dmaengine_prep_dma_memset(
> struct dma_chan *chan, dma_addr_t dest, int value, size_t len,
> unsigned long flags)
>
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