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

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Hi Sengyu,

Am 18.06.23 um 21:43 schrieb Shengyu Qu:
Hello Stefan,

Sorry to reply to this old series, but I wonder what happens to this series?

i never found the time to prepare a newer version. Unfortunately the downstream kernel had a lot of changes regarding this feature recently.


Best regards,

Shengyu

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




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