Re: [PATCH 2/3] riscv: dts: spacemit: Move UARTs under dma-bus for K1

[Vivian Wang <wangruikang@iscas.ac.cn>]

On 6/24/25 20:21, Guodong Xu wrote:
> On Mon, Jun 23, 2025 at 6:04 PM Vivian Wang <wangruikang@iscas.ac.cn> wrote:
>> UART devices in Spacemit K1 use dma-bus DMA translations. Move these
>> nodes under dma-bus to reflect this fact.
...
>>
>> -               sec_uart1: serial@f0612000 {
>> -                       compatible = "spacemit,k1-uart", "intel,xscale-uart";
>> -                       reg = <0x0 0xf0612000 0x0 0x100>;
>> -                       interrupts = <43>;
>> -                       clock-frequency = <14857000>;
>> -                       reg-shift = <2>;
>> -                       reg-io-width = <4>;
>> -                       status = "reserved"; /* for TEE usage */
>> -               };
>> -
> Are you sure sec_uart1 should be placed under the dma_bus? Please double
> check. If sec_uart1 and other peripherals supported by the secure DMA
> (base address: 0xF0600000) share the same address mapping as dma_bus, and
> if they can be accessed by the linux kernel in some cases (as saying
> 'reserved'), then that makes sense. If not, better not move them.

Hi Guodong,

I have confirmed with SpacemiT that sec_uart1 uses dram_range4, a.k.a.
dma-bus, which is same as the rest of the UARTs.

Also, sec_uart1 is usable in e.g. Linux, but only if no TEE is in use.
Using status = "reserved" is the safe choice here. Platforms that do not
run a TEE (or anything similar that would disable access to the
0xf000_0000 to 0xffff_ffff range) and wishing to enable use of sec_uart1
can change the status to "okay".

Vivian "dramforever" Wang