[PATCH] riscv: Fix Kendryte K210 device tree

[Sean Anderson]

On 9/15/20 8:55 AM, Damien Le Moal wrote:
> The Kendryte K210 SoC CLINT is compatible with Sifive clint v0
> (sifive,clint0). Fix the Kendryte K210 device tree clint entry to be
> inline with the sifive timer definition documented in
> Documentation/devicetree/bindings/timer/sifive,clint.yaml. Rename the
> clint0 entry to "timer", fix the register mapping and fix the interrupt
> extended entry.
> 
> This fixes boot failures with Kendryte K210 SoC boards.
> 
> Signed-off-by: Damien Le Moal <damien.lemoal at wdc.com>
> ---
>  arch/riscv/boot/dts/kendryte/k210.dtsi | 7 ++++---
>  1 file changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/riscv/boot/dts/kendryte/k210.dtsi b/arch/riscv/boot/dts/kendryte/k210.dtsi
> index c1df56ccb8d5..48d65fea45e9 100644
> --- a/arch/riscv/boot/dts/kendryte/k210.dtsi
> +++ b/arch/riscv/boot/dts/kendryte/k210.dtsi
> @@ -95,10 +95,11 @@ sysctl: sysctl at 50440000 {
>  			#clock-cells = <1>;
>  		};
>  
> -		clint0: interrupt-controller at 2000000 {
> +		timer at 2000000 {
>  			compatible = "riscv,clint0";
> -			reg = <0x2000000 0xC000>;
> -			interrupts-extended = <&cpu0_intc 3>,  <&cpu1_intc 3>;
> +			reg = <0x2000000 0x10000>;

Why the change in size? The docs from the SDK [1] (which I think were copied
from SiFive documentation around the time of their release) state that
the CLINT is 0xC000 bytes. In addition, accessing memory past 0x0200C000
yields a repeating memory pattern:


0200c000: 69823183 02020120 6083c006 00008002    .1.i ......`....
0200c010: 69823183 02020120 6083c006 00008002    .1.i ......`....
0200c020: 69823183 02020120 6083c006 00008002    .1.i ......`....
0200c030: 69823183 02020120 6083c006 00008002    .1.i ......`....
(continues until 0x02010000)

To me, it is clear that the CLINT is not 0x10000 in size, even though
the legal address space extends to that size.

I am more curious how this fixes booting. What was the issue before?

> +			interrupts-extended =  <&cpu0_intc 3 &cpu0_intc 7
> +						&cpu1_intc 3 &cpu1_intc 7>;
>  			clocks = <&sysctl K210_CLK_ACLK>;

This clock is 50 times too fast(!) See [2] and [3] for a fix. I don't
know if adding a "virtual" clock is the best solution for Linux. I would
like to keep the device trees relatively in-sync, so please let me know
if you think there is a better solution.

>  		};
>  
> 

[1] https://github.com/kendryte/kendryte-standalone-sdk/blob/develop/lib/drivers/include/clint.h
[2] https://patchwork.ozlabs.org/project/uboot/patch/20200915141724.503929-8-seanga2@gmail.com/
[3] https://patchwork.ozlabs.org/project/uboot/patch/20200915141724.503929-9-seanga2@gmail.com/