Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx> writes: > STM32 DMA-MDMA chaining feature is available on STM32 SoCs which embed > STM32 DMAMUX, DMA and MDMA controllers. It is the case on STM32MP1 SoCs but > also on STM32H7 SoCs. But focus is on STM32MP1 SoCs, using DDR. > This documentation aims to explain how to use STM32 DMA-MDMA chaining > feature in drivers of STM32 peripheral having request lines on STM32 DMA. > > Signed-off-by: Amelie Delaunay <amelie.delaunay@xxxxxxxxxxx> > --- > .../arm/stm32/stm32-dma-mdma-chaining.rst | 365 ++++++++++++++++++ > 1 file changed, 365 insertions(+) > create mode 100644 Documentation/arm/stm32/stm32-dma-mdma-chaining.rst When you add a new RST file you also need to add it to index.rst somewhere so that it becomes part of the docs build. > diff --git a/Documentation/arm/stm32/stm32-dma-mdma-chaining.rst b/Documentation/arm/stm32/stm32-dma-mdma-chaining.rst > new file mode 100644 > index 000000000000..bfbbadc45aa7 > --- /dev/null > +++ b/Documentation/arm/stm32/stm32-dma-mdma-chaining.rst > @@ -0,0 +1,365 @@ > +.. SPDX-License-Identifier: GPL-2.0 > + > +======================= > +STM32 DMA-MDMA chaining > +======================= > + > + > +Introduction > +------------ > + > + This document describes the STM32 DMA-MDMA chaining feature. But before going further, let's > + introduce the peripherals involved. Please keep to the 80-column limit for documentation, it makes it easier to read. > + To offload data transfers from the CPU, STM32 microprocessors (MPUs) embed direct memory access > + controllers (DMA). > + > + STM32MP1 SoCs embed both STM32 DMA and STM32 MDMA controllers. STM32 DMA request routing > + capabilities are enhanced by a DMA request multiplexer (STM32 DMAMUX). > + > + **STM32 DMAMUX** > + > + STM32 DMAMUX routes any DMA request from a given peripheral to any STM32 DMA controller (STM32MP1 > + counts two STM32 DMA controllers) channels. > + > + **STM32 DMA** > + > + STM32 DMA is mainly used to implement central data buffer storage (usually in the system SRAM) for > + different peripheral. It can access external RAMs but without the ability to generate convenient > + burst transfer ensuring the best load of the AXI. > + > + **STM32 MDMA** > + > + STM32 MDMA (Master DMA) is mainly used to manage direct data transfers between RAM data buffers > + without CPU intervention. It can also be used in a hierarchical structure that uses STM32 DMA as > + first level data buffer interfaces for AHB peripherals, while the STM32 MDMA acts as a second > + level DMA with better performance. As a AXI/AHB master, STM32 MDMA can take control of the AXI/AHB > + bus. > + > + > +Principles > +---------- > + > + STM32 DMA-MDMA chaining feature relies on the strengths of STM32 DMA and STM32 MDMA controllers. > + > + STM32 DMA has a circular Double Buffer Mode (DBM). At each end of transaction (when DMA data > + counter - DMA_SxNDTR - reaches 0), the memory pointers (configured with DMA_SxSM0AR and > + DMA_SxM1AR) are swapped and the DMA data counter is automatically reloaded. This allows the SW or > + the STM32 MDMA to process one memory area while the second memory area is being filled/used by the > + STM32 DMA transfer. > + > + With STM32 MDMA linked-list mode, a single request initiates the data array (collection of nodes) > + to be transferred until the linked-list pointer for the channel is null. The channel transfer > + complete of the last node is the end of transfer, unless first and last nodes are linked to each > + other, in such a case, the linked-list loops on to create a circular MDMA transfer. > + > + STM32 MDMA has direct connections with STM32 DMA. This enables autonomous communication and > + synchronization between peripherals, thus saving CPU resources and bus congestion. Transfer > + Complete signal of STM32 DMA channel can triggers STM32 MDMA transfer. STM32 MDMA can clear the > + request generated by the STM32 DMA by writing to its Interrupt Clear register (whose address is > + stored in MDMA_CxMAR, and bit mask in MDMA_CxMDR). > + > + .. csv-table:: STM32 MDMA interconnect table with STM32 DMA > + :header: "STM32 DMAMUX channels", "STM32 DMA controllers channels", > + "STM32 DMA Transfer Complete signal", "STM32 MDMA request" If at all possible, please use simple tables; that makes the plain text documentation much easier to read. [...] Thanks, jon
