On 10/10/2018 06:03 AM, Vinod wrote: > On 09-10-18, 10:40, Pierre Yves MORDRET wrote: >> >> >> On 10/07/2018 06:00 PM, Vinod wrote: >>> On 28-09-18, 15:01, Pierre-Yves MORDRET wrote: >>>> This patch adds support of DMA/MDMA chaining support. >>>> It introduces an intermediate transfer between peripherals and STM32 DMA. >>>> This intermediate transfer is triggered by SW for single M2D transfer and >>>> by STM32 DMA IP for all other modes (sg, cyclic) and direction (D2M). >>>> >>>> A generic SRAM allocator is used for this intermediate buffer >>>> Each DMA channel will be able to define its SRAM needs to achieve chaining >>>> feature : (2 ^ order) * PAGE_SIZE. >>>> For cyclic, SRAM buffer is derived from period length (rounded on >>>> PAGE_SIZE). >>> >>> So IIUC, you chain two dma txns together and transfer data via an SRAM? >> >> Correct. one DMA is DMAv2 (stm32-dma) and the other is MDMA(stm32-mdma). >> Intermediate transfer is between device and memory. >> This intermediate transfer is using SDRAM. > > Ah so you use dma calls to setup mdma xtfers? I dont think that is a > good idea. How do you know you should use mdma for subsequent transfer? > When user bindings told to setup chaining intermediate MDMA transfers are always triggers. For instance if a user requests a Dev2Mem transfer with chaining. From client pov this is still a prep_slave_sg. Internally DMAv2 is setup in cyclic mode (in double buffer mode indeed => 2 buffer of PAGE_SIZE/2) and destination is SDRAM. DMAv2 will flip/flop on those 2 buffers. At the same time DMAv2 driver prepares a MDMA SG that will fetch data from those 2 buffers in SDRAM and fills final destination memory. > >>>> drivers/dma/stm32-dma.c | 879 ++++++++++++++++++++++++++++++++++++++++++------ >>> >>> that is a lot of change for a driver, consider splitting it up >>> logically in smaller changes... >>> >> >> This feature is rather monolithic. Difficult to split up. >> All the code is required at once. > > It can be enabled at last but split up logically. Intrusive changes to a > driver make it hard to review.. > Ok. I will to think about it how to proceed.
