diff options
Diffstat (limited to 'Documentation/arch/arm/stm32/stm32-dma-mdma-chaining.rst')
| -rw-r--r-- | Documentation/arch/arm/stm32/stm32-dma-mdma-chaining.rst | 415 |
1 files changed, 415 insertions, 0 deletions
diff --git a/Documentation/arch/arm/stm32/stm32-dma-mdma-chaining.rst b/Documentation/arch/arm/stm32/stm32-dma-mdma-chaining.rst new file mode 100644 index 0000000000..2945e0e331 --- /dev/null +++ b/Documentation/arch/arm/stm32/stm32-dma-mdma-chaining.rst @@ -0,0 +1,415 @@ +.. 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. + + 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). + + .. table:: STM32 MDMA interconnect table with STM32 DMA + + +--------------+----------------+-----------+------------+ + | STM32 DMAMUX | STM32 DMA | STM32 DMA | STM32 MDMA | + | channels | channels | Transfer | request | + | | | complete | | + | | | signal | | + +==============+================+===========+============+ + | Channel *0* | DMA1 channel 0 | dma1_tcf0 | *0x00* | + +--------------+----------------+-----------+------------+ + | Channel *1* | DMA1 channel 1 | dma1_tcf1 | *0x01* | + +--------------+----------------+-----------+------------+ + | Channel *2* | DMA1 channel 2 | dma1_tcf2 | *0x02* | + +--------------+----------------+-----------+------------+ + | Channel *3* | DMA1 channel 3 | dma1_tcf3 | *0x03* | + +--------------+----------------+-----------+------------+ + | Channel *4* | DMA1 channel 4 | dma1_tcf4 | *0x04* | + +--------------+----------------+-----------+------------+ + | Channel *5* | DMA1 channel 5 | dma1_tcf5 | *0x05* | + +--------------+----------------+-----------+------------+ + | Channel *6* | DMA1 channel 6 | dma1_tcf6 | *0x06* | + +--------------+----------------+-----------+------------+ + | Channel *7* | DMA1 channel 7 | dma1_tcf7 | *0x07* | + +--------------+----------------+-----------+------------+ + | Channel *8* | DMA2 channel 0 | dma2_tcf0 | *0x08* | + +--------------+----------------+-----------+------------+ + | Channel *9* | DMA2 channel 1 | dma2_tcf1 | *0x09* | + +--------------+----------------+-----------+------------+ + | Channel *10* | DMA2 channel 2 | dma2_tcf2 | *0x0A* | + +--------------+----------------+-----------+------------+ + | Channel *11* | DMA2 channel 3 | dma2_tcf3 | *0x0B* | + +--------------+----------------+-----------+------------+ + | Channel *12* | DMA2 channel 4 | dma2_tcf4 | *0x0C* | + +--------------+----------------+-----------+------------+ + | Channel *13* | DMA2 channel 5 | dma2_tcf5 | *0x0D* | + +--------------+----------------+-----------+------------+ + | Channel *14* | DMA2 channel 6 | dma2_tcf6 | *0x0E* | + +--------------+----------------+-----------+------------+ + | Channel *15* | DMA2 channel 7 | dma2_tcf7 | *0x0F* | + +--------------+----------------+-----------+------------+ + + STM32 DMA-MDMA chaining feature then uses a SRAM buffer. STM32MP1 SoCs embed + three fast access static internal RAMs of various size, used for data storage. + Due to STM32 DMA legacy (within microcontrollers), STM32 DMA performances are + bad with DDR, while they are optimal with SRAM. Hence the SRAM buffer used + between STM32 DMA and STM32 MDMA. This buffer is split in two equal periods + and STM32 DMA uses one period while STM32 MDMA uses the other period + simultaneously. + :: + + dma[1:2]-tcf[0:7] + .----------------. + ____________ ' _________ V____________ + | STM32 DMA | / __|>_ \ | STM32 MDMA | + |------------| | / \ | |------------| + | DMA_SxM0AR |<=>| | SRAM | |<=>| []-[]...[] | + | DMA_SxM1AR | | \_____/ | | | + |____________| \___<|____/ |____________| + + STM32 DMA-MDMA chaining uses (struct dma_slave_config).peripheral_config to + exchange the parameters needed to configure MDMA. These parameters are + gathered into a u32 array with three values: + + * the STM32 MDMA request (which is actually the DMAMUX channel ID), + * the address of the STM32 DMA register to clear the Transfer Complete + interrupt flag, + * the mask of the Transfer Complete interrupt flag of the STM32 DMA channel. + +Device Tree updates for STM32 DMA-MDMA chaining support +------------------------------------------------------- + + **1. Allocate a SRAM buffer** + + SRAM device tree node is defined in SoC device tree. You can refer to it in + your board device tree to define your SRAM pool. + :: + + &sram { + my_foo_device_dma_pool: dma-sram@0 { + reg = <0x0 0x1000>; + }; + }; + + Be careful of the start index, in case there are other SRAM consumers. + Define your pool size strategically: to optimise chaining, the idea is that + STM32 DMA and STM32 MDMA can work simultaneously, on each buffer of the + SRAM. + If the SRAM period is greater than the expected DMA transfer, then STM32 DMA + and STM32 MDMA will work sequentially instead of simultaneously. It is not a + functional issue but it is not optimal. + + Don't forget to refer to your SRAM pool in your device node. You need to + define a new property. + :: + + &my_foo_device { + ... + my_dma_pool = &my_foo_device_dma_pool; + }; + + Then get this SRAM pool in your foo driver and allocate your SRAM buffer. + + **2. Allocate a STM32 DMA channel and a STM32 MDMA channel** + + You need to define an extra channel in your device tree node, in addition to + the one you should already have for "classic" DMA operation. + + This new channel must be taken from STM32 MDMA channels, so, the phandle of + the DMA controller to use is the MDMA controller's one. + :: + + &my_foo_device { + [...] + my_dma_pool = &my_foo_device_dma_pool; + dmas = <&dmamux1 ...>, // STM32 DMA channel + <&mdma1 0 0x3 0x1200000a 0 0>; // + STM32 MDMA channel + }; + + Concerning STM32 MDMA bindings: + + 1. The request line number : whatever the value here, it will be overwritten + by MDMA driver with the STM32 DMAMUX channel ID passed through + (struct dma_slave_config).peripheral_config + + 2. The priority level : choose Very High (0x3) so that your channel will + take priority other the other during request arbitration + + 3. A 32bit mask specifying the DMA channel configuration : source and + destination address increment, block transfer with 128 bytes per single + transfer + + 4. The 32bit value specifying the register to be used to acknowledge the + request: it will be overwritten by MDMA driver, with the DMA channel + interrupt flag clear register address passed through + (struct dma_slave_config).peripheral_config + + 5. The 32bit mask specifying the value to be written to acknowledge the + request: it will be overwritten by MDMA driver, with the DMA channel + Transfer Complete flag passed through + (struct dma_slave_config).peripheral_config + +Driver updates for STM32 DMA-MDMA chaining support in foo driver +---------------------------------------------------------------- + + **0. (optional) Refactor the original sg_table if dmaengine_prep_slave_sg()** + + In case of dmaengine_prep_slave_sg(), the original sg_table can't be used as + is. Two new sg_tables must be created from the original one. One for + STM32 DMA transfer (where memory address targets now the SRAM buffer instead + of DDR buffer) and one for STM32 MDMA transfer (where memory address targets + the DDR buffer). + + The new sg_list items must fit SRAM period length. Here is an example for + DMA_DEV_TO_MEM: + :: + + /* + * Assuming sgl and nents, respectively the initial scatterlist and its + * length. + * Assuming sram_dma_buf and sram_period, respectively the memory + * allocated from the pool for DMA usage, and the length of the period, + * which is half of the sram_buf size. + */ + struct sg_table new_dma_sgt, new_mdma_sgt; + struct scatterlist *s, *_sgl; + dma_addr_t ddr_dma_buf; + u32 new_nents = 0, len; + int i; + + /* Count the number of entries needed */ + for_each_sg(sgl, s, nents, i) + if (sg_dma_len(s) > sram_period) + new_nents += DIV_ROUND_UP(sg_dma_len(s), sram_period); + else + new_nents++; + + /* Create sg table for STM32 DMA channel */ + ret = sg_alloc_table(&new_dma_sgt, new_nents, GFP_ATOMIC); + if (ret) + dev_err(dev, "DMA sg table alloc failed\n"); + + for_each_sg(new_dma_sgt.sgl, s, new_dma_sgt.nents, i) { + _sgl = sgl; + sg_dma_len(s) = min(sg_dma_len(_sgl), sram_period); + /* Targets the beginning = first half of the sram_buf */ + s->dma_address = sram_buf; + /* + * Targets the second half of the sram_buf + * for odd indexes of the item of the sg_list + */ + if (i & 1) + s->dma_address += sram_period; + } + + /* Create sg table for STM32 MDMA channel */ + ret = sg_alloc_table(&new_mdma_sgt, new_nents, GFP_ATOMIC); + if (ret) + dev_err(dev, "MDMA sg_table alloc failed\n"); + + _sgl = sgl; + len = sg_dma_len(sgl); + ddr_dma_buf = sg_dma_address(sgl); + for_each_sg(mdma_sgt.sgl, s, mdma_sgt.nents, i) { + size_t bytes = min_t(size_t, len, sram_period); + + sg_dma_len(s) = bytes; + sg_dma_address(s) = ddr_dma_buf; + len -= bytes; + + if (!len && sg_next(_sgl)) { + _sgl = sg_next(_sgl); + len = sg_dma_len(_sgl); + ddr_dma_buf = sg_dma_address(_sgl); + } else { + ddr_dma_buf += bytes; + } + } + + Don't forget to release these new sg_tables after getting the descriptors + with dmaengine_prep_slave_sg(). + + **1. Set controller specific parameters** + + First, use dmaengine_slave_config() with a struct dma_slave_config to + configure STM32 DMA channel. You just have to take care of DMA addresses, + the memory address (depending on the transfer direction) must point on your + SRAM buffer, and set (struct dma_slave_config).peripheral_size != 0. + + STM32 DMA driver will check (struct dma_slave_config).peripheral_size to + determine if chaining is being used or not. If it is used, then STM32 DMA + driver fills (struct dma_slave_config).peripheral_config with an array of + three u32 : the first one containing STM32 DMAMUX channel ID, the second one + the channel interrupt flag clear register address, and the third one the + channel Transfer Complete flag mask. + + Then, use dmaengine_slave_config with another struct dma_slave_config to + configure STM32 MDMA channel. Take care of DMA addresses, the device address + (depending on the transfer direction) must point on your SRAM buffer, and + the memory address must point to the buffer originally used for "classic" + DMA operation. Use the previous (struct dma_slave_config).peripheral_size + and .peripheral_config that have been updated by STM32 DMA driver, to set + (struct dma_slave_config).peripheral_size and .peripheral_config of the + struct dma_slave_config to configure STM32 MDMA channel. + :: + + struct dma_slave_config dma_conf; + struct dma_slave_config mdma_conf; + + memset(&dma_conf, 0, sizeof(dma_conf)); + [...] + config.direction = DMA_DEV_TO_MEM; + config.dst_addr = sram_dma_buf; // SRAM buffer + config.peripheral_size = 1; // peripheral_size != 0 => chaining + + dmaengine_slave_config(dma_chan, &dma_config); + + memset(&mdma_conf, 0, sizeof(mdma_conf)); + config.direction = DMA_DEV_TO_MEM; + mdma_conf.src_addr = sram_dma_buf; // SRAM buffer + mdma_conf.dst_addr = rx_dma_buf; // original memory buffer + mdma_conf.peripheral_size = dma_conf.peripheral_size; // <- dma_conf + mdma_conf.peripheral_config = dma_config.peripheral_config; // <- dma_conf + + dmaengine_slave_config(mdma_chan, &mdma_conf); + + **2. Get a descriptor for STM32 DMA channel transaction** + + In the same way you get your descriptor for your "classic" DMA operation, + you just have to replace the original sg_list (in case of + dmaengine_prep_slave_sg()) with the new sg_list using SRAM buffer, or to + replace the original buffer address, length and period (in case of + dmaengine_prep_dma_cyclic()) with the new SRAM buffer. + + **3. Get a descriptor for STM32 MDMA channel transaction** + + If you previously get descriptor (for STM32 DMA) with + + * dmaengine_prep_slave_sg(), then use dmaengine_prep_slave_sg() for + STM32 MDMA; + * dmaengine_prep_dma_cyclic(), then use dmaengine_prep_dma_cyclic() for + STM32 MDMA. + + Use the new sg_list using SRAM buffer (in case of dmaengine_prep_slave_sg()) + or, depending on the transfer direction, either the original DDR buffer (in + case of DMA_DEV_TO_MEM) or the SRAM buffer (in case of DMA_MEM_TO_DEV), the + source address being previously set with dmaengine_slave_config(). + + **4. Submit both transactions** + + Before submitting your transactions, you may need to define on which + descriptor you want a callback to be called at the end of the transfer + (dmaengine_prep_slave_sg()) or the period (dmaengine_prep_dma_cyclic()). + Depending on the direction, set the callback on the descriptor that finishes + the overal transfer: + + * DMA_DEV_TO_MEM: set the callback on the "MDMA" descriptor + * DMA_MEM_TO_DEV: set the callback on the "DMA" descriptor + + Then, submit the descriptors whatever the order, with dmaengine_tx_submit(). + + **5. Issue pending requests (and wait for callback notification)** + + As STM32 MDMA channel transfer is triggered by STM32 DMA, you must issue + STM32 MDMA channel before STM32 DMA channel. + + If any, your callback will be called to warn you about the end of the overal + transfer or the period completion. + + Don't forget to terminate both channels. STM32 DMA channel is configured in + cyclic Double-Buffer mode so it won't be disabled by HW, you need to terminate + it. STM32 MDMA channel will be stopped by HW in case of sg transfer, but not + in case of cyclic transfer. You can terminate it whatever the kind of transfer. + + **STM32 DMA-MDMA chaining DMA_MEM_TO_DEV special case** + + STM32 DMA-MDMA chaining in DMA_MEM_TO_DEV is a special case. Indeed, the + STM32 MDMA feeds the SRAM buffer with the DDR data, and the STM32 DMA reads + data from SRAM buffer. So some data (the first period) have to be copied in + SRAM buffer when the STM32 DMA starts to read. + + A trick could be pausing the STM32 DMA channel (that will raise a Transfer + Complete signal, triggering the STM32 MDMA channel), but the first data read + by the STM32 DMA could be "wrong". The proper way is to prepare the first SRAM + period with dmaengine_prep_dma_memcpy(). Then this first period should be + "removed" from the sg or the cyclic transfer. + + Due to this complexity, rather use the STM32 DMA-MDMA chaining for + DMA_DEV_TO_MEM and keep the "classic" DMA usage for DMA_MEM_TO_DEV, unless + you're not afraid. + +Resources +--------- + + Application note, datasheet and reference manual are available on ST website + (STM32MP1_). + + Dedicated focus on three application notes (AN5224_, AN4031_ & AN5001_) + dealing with STM32 DMAMUX, STM32 DMA and STM32 MDMA. + +.. _STM32MP1: https://www.st.com/en/microcontrollers-microprocessors/stm32mp1-series.html +.. _AN5224: https://www.st.com/resource/en/application_note/an5224-stm32-dmamux-the-dma-request-router-stmicroelectronics.pdf +.. _AN4031: https://www.st.com/resource/en/application_note/dm00046011-using-the-stm32f2-stm32f4-and-stm32f7-series-dma-controller-stmicroelectronics.pdf +.. _AN5001: https://www.st.com/resource/en/application_note/an5001-stm32cube-expansion-package-for-stm32h7-series-mdma-stmicroelectronics.pdf + +:Authors: + +- Amelie Delaunay <amelie.delaunay@foss.st.com>
\ No newline at end of file |