Re: [PATCH v5 12/18] dt-bindings: dma: ti: Add K3 BCDMA V2

[Sai Sree Kartheek Adivi]

On 19/02/26 13:13, Krzysztof Kozlowski wrote:

Hi Krzysztof,

Thanks for the review.
> On Wed, Feb 18, 2026 at 03:22:37PM +0530, Sai Sree Kartheek Adivi wrote:
> > New binding document for
> Fix wrapping - it's wrapped too early.
Ack. will fix it in v6.
> > Texas Instruments K3 Block Copy DMA (BCDMA) V2.
> >
> > BCDMA V2 is introduced as part of AM62L.
> >
> > Signed-off-by: Sai Sree Kartheek Adivi <s-adivi@xxxxxx>
> > ---
> >   .../bindings/dma/ti/ti,am62l-dmss-bcdma.yaml  | 120 ++++++++++++++++++
> >   1 file changed, 120 insertions(+)
> >   create mode 100644 Documentation/devicetree/bindings/dma/ti/ti,am62l-dmss-bcdma.yaml
> >
> > diff --git a/Documentation/devicetree/bindings/dma/ti/ti,am62l-dmss-bcdma.yaml b/Documentation/devicetree/bindings/dma/ti/ti,am62l-dmss-bcdma.yaml
> > new file mode 100644
> > index 0000000000000..6fa08f22df375
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/dma/ti/ti,am62l-dmss-bcdma.yaml
> > @@ -0,0 +1,120 @@
> > +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> > +# Copyright (C) 2024-25 Texas Instruments Incorporated
> > +# Author: Sai Sree Kartheek Adivi <s-adivi@xxxxxx>
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/dma/ti/ti,am62l-dmss-bcdma.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Texas Instruments K3 DMSS BCDMA V2
> > +
> > +maintainers:
> > +  - Sai Sree Kartheek Adivi <s-adivi@xxxxxx>
> > +
> > +description:
> > +  The BCDMA V2 is intended to perform similar functions as the TR
> > +  mode channels of K3 UDMA-P.
> > +  BCDMA V2 includes block copy channels and Split channels.
> > +
> > +  Block copy channels mainly used for memory to memory transfers, but with
> > +  optional triggers a block copy channel can service peripherals by accessing
> > +  directly to memory mapped registers or area.
> > +
> > +  Split channels can be used to service PSI-L based peripherals.
> > +  The peripherals can be PSI-L native or legacy, non PSI-L native peripherals
> > +  with PDMAs. PDMA is tasked to act as a bridge between the PSI-L fabric and the
> > +  legacy peripheral.
> > +
> > +allOf:
> > +  - $ref: /schemas/dma/dma-controller.yaml#
> > +
> > +properties:
> > +  compatible:
> > +    const: ti,am62l-dmss-bcdma
> > +
> > +  reg:
> > +    items:
> > +      - description: BCDMA Control & Status Registers region
> > +      - description: Block Copy Channel Realtime Registers region
> > +      - description: Channel Realtime Registers region
> > +      - description: Ring Realtime Registers region
> > +
> > +  reg-names:
> > +    items:
> > +      - const: gcfg
> > +      - const: bchanrt
> > +      - const: chanrt
> > +      - const: ringrt
> > +
> > +  "#address-cells":
> > +    const: 0
> > +
> > +  "#interrupt-cells":
> > +    const: 1
> I don't get why this is nexus but not a interrupt-controller.
>
> Can you point me to DTS with complete picture using this?

Please refer 
https://github.com/sskartheekadivi/linux/commit/4a7078a6892bfbc4c620b9668e3421b4c7405ca4

for the dt nodes of AM62L BCDMA and PKTDMA.

Refer to the below tree for full set of driver, dt-binding and dts changes

https://github.com/sskartheekadivi/linux/commits/dma-upstream-v5/

> > +
> > +  "#dma-cells":
> > +    const: 4
> > +    description: |
> > +      cell 1: Trigger type for the channel
> > +        0 - disable / no trigger
> > +        1 - internal channel event
> > +        2 - external signal
> > +        3 - timer manager event
> > +
> > +      cell 2: parameter for the trigger:
> > +        if cell 1 is 0 (disable / no trigger):
> > +          Unused, ignored
> > +        if cell 1 is 1 (internal channel event):
> > +          channel number whose TR event should trigger the current channel.
> > +        if cell 1 is 2 or 3 (external signal or timer manager event):
> > +          index of global interfaces that come into the DMA.
> > +
> > +          Please refer to the device documentation for global interface indexes.
> > +
> > +      cell 3: Channel number for the peripheral
> > +
> > +        Please refer to the device documentation for the channel map.
> > +
> > +      cell 4: ASEL value for the channel
> > +
> > +  interrupt-map-mask:
> > +    items:
> > +      - const: 0x7ff
> > +
> > +  interrupt-map:
> > +    description: |
> > +      Maps internal BCDMA channel IDs to the parent GIC IRQ lines.
> Isn't this mapping fixed in given device? IOW, not really part of DTS
> description but deducible from the compatible.
>
> You only need to provide interrupts for your device.

I initially considered handling the mapping in the driver based on the

compatible string, but discussing the hardware architecture internally,

that approach becomes highly problematic for this IP block.


While the mapping is fixed for the AM62L specifically, this same BCDMA V2

IP block is reused across different K3 SoCs, and the internal

channel-to-IRQ wiring changes entirely from SoC to SoC. Furthermore, the

mapping of internal channels to the parent GIC interrupts is discontiguous

(and the hardware IP itself supports mapping multiple DMA channels to a

single shared IRQ line, depending on the SoC integration).


If we rely on the driver to deduce this via the compatible string, we will

have to maintain large, discontiguous mapping tables inside the driver

code for every new SoC that integrates this IP.


Because the IP is essentially routing its internal channel events to a

different set of parent IRQs (which varies per SoC integration), using

interrupt-map allows us to accurately describe the specific SoC's wiring

purely in the DT. This keeps the driver clean and easily reusable for

future K3 SoCs without creeping hardware routing tables into the driver

code.


Let me know if this clarifies the use of the nexus properties here.


Best regards,

Kartheek

> Best regards,
> Krzysztof