lkml.org 
[lkml]   [2022]   [Jul]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 1/4] docs: arm: stm32: introduce STM32 DMA-MDMA chaining feature
From


On 7/11/22 17:11, Jonathan Corbet wrote:
> Amelie Delaunay <amelie.delaunay@foss.st.com> 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@foss.st.com>
>> ---
>> .../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.
>

Thanks for you review.

I'll add it to index.rst, with other stm32 documentations.

>> 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.
>

OK, I prepare a v2 with a 80-column limit for the documentation patch.

>> + 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.
>

It is possible, with some extra lines. I'll update it in v2 coming soon.

> [...]
>
> Thanks,
>
> jon

Regards,
Amelie

\
 
 \ /
  Last update: 2022-07-12 15:40    [W:0.050 / U:2.780 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site