Re: [PATCH v8 1/3] dmaengine: Add new device_{set,release}_slave callbacks

Vinod Koul
2017-02-10T04:34:13Z

On Thu, Feb 09, 2017 at 03:22:49PM +0100, Marek Szyprowski wrote:
> Add two new callbacks to DMA engine device. They will used to provide
> access to slave device (the device which requested given DMA channel)

You mean access to client devices?

> for DMA engine driver. Access to slave device might be useful for example
> for implementing advanced runtime power management.
>
> DMA slave channels are exclusive, so only one slave device can be set
> for a given DMA slave channel.

That is not a right assumption and my worry here. With virt-dma we don't
really assume a hardware channel and exclusive. Certain implementation may
do that but from framework we cannot assume that.

> device_set_slave() will be called after the device_alloc_chan_resources()
> and device_release_slave() before the device_free_chan_resources().

Okay, I had to relook at the series to get around this part. Sorry but we
can't call it set_slave, it is actually set_client/consumer

In our context slaves means dmaengine slave devices aka provider.
Client would be the consumer and not slave.

> Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
> ---
> drivers/dma/dmaengine.c | 27 ++++++++++++++++++++++++---
> include/linux/dmaengine.h | 10 ++++++++++
> 2 files changed, 34 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 24e0221fd66d..5b7089d8be4d 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -705,6 +705,7 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> {
> struct dma_device *d, *_d;
> struct dma_chan *chan = NULL;
> + int ret;
>
> /* If device-tree is present get slave info from here */
> if (dev->of_node)
> @@ -715,8 +716,9 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> chan = acpi_dma_request_slave_chan_by_name(dev, name);
>
> if (chan) {
> - /* Valid channel found or requester need to be deferred */
> - if (!IS_ERR(chan) || PTR_ERR(chan) == -EPROBE_DEFER)
> + if (!IS_ERR(chan))
> + goto found;
> + if (PTR_ERR(chan) == -EPROBE_DEFER)
> return chan;
> }
>
> @@ -738,7 +740,21 @@ struct dma_chan *dma_request_chan(struct device *dev, const char *name)
> }
> mutex_unlock(&dma_list_mutex);
>
> - return chan ? chan : ERR_PTR(-EPROBE_DEFER);
> + if (!chan)
> + return ERR_PTR(-EPROBE_DEFER);
> + if (IS_ERR(chan))
> + return chan;
> +found:
> + if (chan->device->device_set_slave) {
> + chan->slave = dev;
> + ret = chan->device->device_set_slave(chan, dev);
> + if (ret) {
> + chan->slave = NULL;
> + dma_release_channel(chan);
> + chan = ERR_PTR(ret);
> + }
> + }
> + return chan;
> }
> EXPORT_SYMBOL_GPL(dma_request_chan);
>
> @@ -786,6 +802,11 @@ void dma_release_channel(struct dma_chan *chan)
> mutex_lock(&dma_list_mutex);
> WARN_ONCE(chan->client_count != 1,
> "chan reference count %d != 1\n", chan->client_count);
> + if (chan->slave) {
> + if (chan->device->device_release_slave)
> + chan->device->device_release_slave(chan);
> + chan->slave = NULL;
> + }
> dma_chan_put(chan);
> /* drop PRIVATE cap enabled by __dma_request_channel() */
> if (--chan->device->privatecnt == 0)
> diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> index 533680860865..d22299e37e69 100644
> --- a/include/linux/dmaengine.h
> +++ b/include/linux/dmaengine.h
> @@ -277,6 +277,9 @@ struct dma_chan {
> struct dma_router *router;
> void *route_data;
>
> + /* Only for SLAVE channels */
> + struct device *slave;

so assuming you refer to consumer aka client here, why do we need set if we
store it here.

> +
> void *private;
> };
>
> @@ -686,6 +689,10 @@ struct dma_filter {
> * @device_alloc_chan_resources: allocate resources and return the
> * number of allocated descriptors
> * @device_free_chan_resources: release DMA channel's resources
> + * @device_set_slave: provide access to the slave device, which requested
> + * given DMA channel, called after @device_alloc_chan_resources
> + * @device_release_slave: finishes access to the slave device, called
> + * before @device_free_chan_resources
> * @device_prep_dma_memcpy: prepares a memcpy operation
> * @device_prep_dma_xor: prepares a xor operation
> * @device_prep_dma_xor_val: prepares a xor validation operation
> @@ -746,6 +753,9 @@ struct dma_device {
> int (*device_alloc_chan_resources)(struct dma_chan *chan);
> void (*device_free_chan_resources)(struct dma_chan *chan);
>
> + int (*device_set_slave)(struct dma_chan *chan, struct device *slave);
> + void (*device_release_slave)(struct dma_chan *chan);
> +
> struct dma_async_tx_descriptor *(*device_prep_dma_memcpy)(
> struct dma_chan *chan, dma_addr_t dst, dma_addr_t src,
> size_t len, unsigned long flags);
> --
> 1.9.1
>

--
~Vinod