This patch series provides OMAP sDMA driver changes for descriptor autoloading
feature.
Descriptor autoloading is OMAP4 sDMA hardware capability that can be
exploited for scatter gather scenarios.
The feature works as described below
1) A sDMA channel is programmed to be in 'linked list' mode
2) The client (sDMA user) provides a list of descriptors in a linked list format
3) Each of the 'descriptor' (element in the linked list) contains an updated
set of DMA configuration register values
4) Client starts DMA transfer
5) sDMA controller loads the first element to its register configuration memory
and executes the transfer
6) After completion, loads the next element (in linked list) to configuration
memory and executes the transfer, without MCU intervention.
7) Interrupt is generated after all transfers are completed; this can be
configured to be done differently.
Configurations and additional features
1) Fast mode & non-fast mode
Fast mode/non-fast decides on how the first transfer begins. In
non-fast mode, the first element in the linked list is loaded only after
completing the transfer according to the configurations already in the sDMA
channel registers. In fast mode, the loading of the first element precedes the
transfer.
2) Pause / resume of transfers
A transfer can be paused after a descriptor set has been loaded,
provided the 'pause bit' is set in the linked list element.
An ongoing transfer cannot be paused. If the 'pause bit' is set, transfer is
not started after loading the register set from memory.
Such a transfer can be resumed later.
3) Descriptor types
3 possible configurations of descriptors (initialized as linked list
elements) are possible. Type 1 provides the maximum flexibility, which contains
most register definitions of a DMA logical channel. Fewer options are present
in type 2. Type 3 can just modify source/destinations address of transfers. In
all transfers, unmodified registers settings are maintained for the next
transfer.
Patch provides options / API for
1) Setting up a descriptor loading for DMA channel for sg type transfers
2) configuration with linked list elements
3) Starting / pause and resume of the said transfers
4) Closing/Releasing the DMA channel
The patches are generated against kernel 2.6.31-rc1, tested on OMAP4 simulator
platform.
Patch List
[Patch 1/2] Adding a new OMAP Kernel configuration option
CONFIG_OMAP_DMA_DESCRIPTOR_FEATURE
[Patch 2/2] sDMA driver support for descriptor autoloading feature.
Comments requested.
Regards,
Venkat.
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