[RFC,00/11] dmaengine: bcm2835: add BCM2711 40-bit DMA support

The BCM2711 has 4 DMA channels with a 40-bit address range, allowing them
to access the full 4GB of memory on a Pi 4. This patch series serves as a
basis for a discussion (just compile tested, so don't expect anything working)
which include the following points:

* correct DT binding and representation for BCM2711

According to the vendor DTS [1] the 4 DMA channels are connected to SCB.
I'm not sure how this is properly adapted to the mainline DT.

* general implementation approach

The vendor approach mapped all the BCM2835 control block bits to the BCM2711
layout and the rest of the differences are handled by a lot of is_40bit_channel
conditions. An advantage of this is the small amount of changes to the driver.
But on the down side the code is now much harder to understand and maintain.

This series tries to implement this feature in a more cleaner way
while keeping it in the bcm2835-dma driver. Before this series the driver
has ~ 1000 lines and after that ~ 1500 lines.

So the question is this approach acceptable?

Patches 1 - 3 are just clean-ups.

Disclaimer: my knowledge about the DMA controller is very limited

More information:

https://datasheets.raspberrypi.com/bcm2711/bcm2711-peripherals.pdf

[1] - https://github.com/raspberrypi/linux/blob/561deffcf471ba0f7bd48541d06a79d5aa38d297/arch/arm/boot/dts/bcm2711-rpi-ds.dtsi#L47
[2] - https://github.com/raspberrypi/linux/commit/44364bd140b0bc9187c881fbdc4ee358961059d5

Stefan Wahren (11):
  ARM: dts: bcm283x: Update DMA node name per DT schema
  dt-bindings: dma: Convert brcm,bcm2835-dma to json-schema
  dmaengine: bcm2835: Support common dma-channel-mask
  dmaengine: bcm2835: move CB info generation into separate function
  dmaengine: bcm2835: move CB final extra info generation into function
  dmaengine: bcm2835: make address increment platform independent
  dmaengine: bcm2385: drop info parameters
  dmaengine: bcm2835: pass dma_chan to generic functions
  dmaengine: bcm2835: introduce multi platform support
  dmaengine: bcm2835: add BCM2711 40-bit DMA support
  ARM: dts: bcm2711: add bcm2711-dma node

 .../devicetree/bindings/dma/brcm,bcm2835-dma.txt   |  83 ---
 .../devicetree/bindings/dma/brcm,bcm2835-dma.yaml  | 107 +++
 arch/arm/boot/dts/bcm2711.dtsi                     |  18 +-
 arch/arm/boot/dts/bcm2835-common.dtsi              |   2 +-
 drivers/dma/bcm2835-dma.c                          | 745 +++++++++++++++++----
 5 files changed, 734 insertions(+), 221 deletions(-)
 delete mode 100644 Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.txt
 create mode 100644 Documentation/devicetree/bindings/dma/brcm,bcm2835-dma.yaml

Hi,

Am 27.12.21 um 13:05 schrieb Stefan Wahren:
> The BCM2711 has 4 DMA channels with a 40-bit address range, allowing them
> to access the full 4GB of memory on a Pi 4. This patch series serves as a
> basis for a discussion (just compile tested, so don't expect anything working)
> which include the following points:
>
> * correct DT binding and representation for BCM2711
>
> According to the vendor DTS [1] the 4 DMA channels are connected to SCB.
> I'm not sure how this is properly adapted to the mainline DT.
>
> * general implementation approach
>
> The vendor approach mapped all the BCM2835 control block bits to the BCM2711
> layout and the rest of the differences are handled by a lot of is_40bit_channel
> conditions. An advantage of this is the small amount of changes to the driver.
> But on the down side the code is now much harder to understand and maintain.
>
> This series tries to implement this feature in a more cleaner way
> while keeping it in the bcm2835-dma driver. Before this series the driver
> has ~ 1000 lines and after that ~ 1500 lines.
>
> So the question is this approach acceptable?
>
> Patches 1 - 3 are just clean-ups.
>
> Disclaimer: my knowledge about the DMA controller is very limited
>
> More information:
>
> https://datasheets.raspberrypi.com/bcm2711/bcm2711-peripherals.pdf
>
> [1] - https://github.com/raspberrypi/linux/blob/561deffcf471ba0f7bd48541d06a79d5aa38d297/arch/arm/boot/dts/bcm2711-rpi-ds.dtsi#L47
> [2] - https://github.com/raspberrypi/linux/commit/44364bd140b0bc9187c881fbdc4ee358961059d5
would be nice to get some input aka gentle ping.