[PATCH RFC] riscv: dts: spacemit: Add DMA translation buses for K1

Vivian Wang
2025-06-17T05:22:04Z

The SpacemiT K1 has various static translations of DMA accesses. Add
these as simple-bus nodes. Devices actually using these translation will
be added in later patches.

The bus names are assigned according to consensus with SpacemiT [1].

[1] https://lore.kernel.org/all/CAH1PCMaC+imcMZCFYtRdmH6ge=dPgnANn_GqVfsGRS=+YhyJCw@mail.gmail.com/

Signed-off-by: Vivian Wang <wangruikang@iscas.ac.cn>
---
This is my concrete proposal for representing DMA translations for
SpacemiT K1.

For context, memory on the SpacemiT K1 is split into two chunks:

- 0x0000_0000 to 0x8000_0000: First 2 GiB of memory
- 0x1_0000_0000 above: Rest of memory

DMA-capable devices on the K1 all have access to the lower 2G of memory
through an identity mapping. However, for the upper region of memory,
each device falls under one of six different mappings. The mappings are
provided in this patch as simple-bus nodes that device nodes should be
added to.

This patch is an RFC because it is not meant to be applied, or at least,
not certainly meant to be applied. Instead, this is an attempt to come
to a consensus on how these bus nodes should look like.

More specifically, I propose that the process proceeds as follows:

- Firstly, relevant parties agree on these bus nodes given here.
- After that, each time the first user of a bus appears, the series
should include a patch to add the bus required for that driver.
- If a driver being submitted uses the same bus as another one that has
been submitted but hasn't yet landed, it can depend on the bus patch
from that previous series.

For conventions regarding coding style, I propose that:

- #address-cells and #size-cells are 2 for consistency
- These bus nodes are put at the end of /soc, inside /soc
- These bus nodes are sorted alphabetically, not in vendor's order
- Devices are added into *-bus nodes directly, not appended towards the
end with a label reference

The K1 DMA translations are *not* interconnects, since they do not
provide any configuration capabilities.

These bus nodes names and properties are provided compliant with
"simple-bus" bindings, and should pass "make dtbs_check".

Remaining questions:

- Should storage-bus exist? Or should drivers under it simply specify
32-bit DMA?
---
arch/riscv/boot/dts/spacemit/k1.dtsi | 53 ++++++++++++++++++++++++++++++++++++
1 file changed, 53 insertions(+)

diff --git a/arch/riscv/boot/dts/spacemit/k1.dtsi b/arch/riscv/boot/dts/spacemit/k1.dtsi
index c0f8c5fca975d73b6ea6886da13fcf55289cb16c..efefed21b9fa1ab9c6ac3d24cd0cca8958b85184 100644
--- a/arch/riscv/boot/dts/spacemit/k1.dtsi
+++ b/arch/riscv/boot/dts/spacemit/k1.dtsi
@@ -562,5 +562,58 @@ sec_uart1: serial@f0612000 {
reg-io-width = <4>;
status = "reserved"; /* for TEE usage */
};
+
+ camera-bus {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>,
+ <0x0 0x80000000 0x1 0x00000000 0x1 0x80000000>;
+ };
+
+ dma-bus {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>,
+ <0x1 0x00000000 0x1 0x80000000 0x3 0x00000000>;
+ };
+
+ multimedia-bus {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>,
+ <0x0 0x80000000 0x1 0x00000000 0x3 0x80000000>;
+ };
+
+ network-bus {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>,
+ <0x0 0x80000000 0x1 0x00000000 0x0 0x80000000>;
+ };
+
+ pcie-bus {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>,
+ <0x0 0xb8000000 0x1 0x38000000 0x3 0x48000000>;
+ };
+
+ storage-bus {
+ compatible = "simple-bus";
+ ranges;
+ #address-cells = <2>;
+ #size-cells = <2>;
+ dma-ranges = <0x0 0x00000000 0x0 0x00000000 0x0 0x80000000>;
+ };
};
};

---
base-commit: 19272b37aa4f83ca52bdf9c16d5d81bdd1354494
change-id: 20250616-k1-dma-buses-rfc-wip-3be7a01f47c8

Best regards,
--
Vivian "dramforever" Wang