dmaengine: core: Introduce new, universal API to request a channel

The two API function can cover most, if not all current APIs used to
request a channel. With minimal effort dmaengine drivers, platforms and
dmaengine user drivers can be converted to use the two function.

struct dma_chan *dma_request_chan_by_mask(const dma_cap_mask_t *mask);

To request any channel matching with the requested capabilities, can be
used to request channel for memcpy, memset, xor, etc where no hardware
synchronization is needed.

struct dma_chan *dma_request_chan(struct device *dev, const char *name);
To request a slave channel. The dma_request_chan() will try to find the
channel via DT, ACPI or in case if the kernel booted in non DT/ACPI mode
it will use a filter lookup table and retrieves the needed information from
the dma_slave_map provided by the DMA drivers.
This legacy mode needs changes in platform code, in dmaengine drivers and
finally the dmaengine user drivers can be converted:

For each dmaengine driver an array of DMA device, slave and the parameter
for the filter function needs to be added:

static const struct dma_slave_map da830_edma_map[] = {
	{ "davinci-mcasp.0", "rx", EDMA_FILTER_PARAM(0, 0) },
	{ "davinci-mcasp.0", "tx", EDMA_FILTER_PARAM(0, 1) },
	{ "davinci-mcasp.1", "rx", EDMA_FILTER_PARAM(0, 2) },
	{ "davinci-mcasp.1", "tx", EDMA_FILTER_PARAM(0, 3) },
	{ "davinci-mcasp.2", "rx", EDMA_FILTER_PARAM(0, 4) },
	{ "davinci-mcasp.2", "tx", EDMA_FILTER_PARAM(0, 5) },
	{ "spi_davinci.0", "rx", EDMA_FILTER_PARAM(0, 14) },
	{ "spi_davinci.0", "tx", EDMA_FILTER_PARAM(0, 15) },
	{ "da830-mmc.0", "rx", EDMA_FILTER_PARAM(0, 16) },
	{ "da830-mmc.0", "tx", EDMA_FILTER_PARAM(0, 17) },
	{ "spi_davinci.1", "rx", EDMA_FILTER_PARAM(0, 18) },
	{ "spi_davinci.1", "tx", EDMA_FILTER_PARAM(0, 19) },
};

This information is going to be needed by the dmaengine driver, so
modification to the platform_data is needed, and the driver map should be
added to the pdata of the DMA driver:

da8xx_edma0_pdata.slave_map = da830_edma_map;
da8xx_edma0_pdata.slavecnt = ARRAY_SIZE(da830_edma_map);

The DMA driver then needs to configure the needed device -> filter_fn
mapping before it registers with dma_async_device_register() :

ecc->dma_slave.filter_map.map = info->slave_map;
ecc->dma_slave.filter_map.mapcnt = info->slavecnt;
ecc->dma_slave.filter_map.fn = edma_filter_fn;

When neither DT or ACPI lookup is available the dma_request_chan() will
try to match the requester's device name with the filter_map's list of
device names, when a match found it will use the information from the
dma_slave_map to get the channel with the dma_get_channel() internal
function.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>

1 files changed, 6 insertions, 17 deletions

diff --git a/Documentation/dmaengine/client.txt b/Documentation/dmaengine/client.txt
index 11fb87ff6cd0..4b04d8988708 100644
--- a/Documentation/dmaengine/client.txt
+++ b/Documentation/dmaengine/client.txt
@@ -22,25 +22,14 @@ The slave DMA usage consists of following steps:
    Channel allocation is slightly different in the slave DMA context,
    client drivers typically need a channel from a particular DMA
    controller only and even in some cases a specific channel is desired.
-   To request a channel dma_request_channel() API is used.
+   To request a channel dma_request_chan() API is used.
 
    Interface:
-        struct dma_chan *dma_request_channel(dma_cap_mask_t mask,
-                        dma_filter_fn filter_fn,
-                        void *filter_param);
-   where dma_filter_fn is defined as:
-        typedef bool (*dma_filter_fn)(struct dma_chan *chan, void *filter_param);
-
-   The 'filter_fn' parameter is optional, but highly recommended for
-   slave and cyclic channels as they typically need to obtain a specific
-   DMA channel.
-
-   When the optional 'filter_fn' parameter is NULL, dma_request_channel()
-   simply returns the first channel that satisfies the capability mask.
-
-   Otherwise, the 'filter_fn' routine will be called once for each free
-   channel which has a capability in 'mask'.  'filter_fn' is expected to
-   return 'true' when the desired DMA channel is found.
+        struct dma_chan *dma_request_chan(struct device *dev, const char *name);
+
+   Which will find and return the 'name' DMA channel associated with the 'dev'
+   device. The association is done via DT, ACPI or board file based
+   dma_slave_map matching table.
 
    A channel allocated via this interface is exclusive to the caller,
    until dma_release_channel() is called.