Re: [PATCH 1/1] riscv: dts: microchip: correct L2 cache interrupts

[<Conor.Dooley@microchip.com>]

Hey Heinrich,
Interesting CC list you got there! Surprised the mailmap didn't sort
out Atish & Krzysztof's addresses, but I think I've fixed them up.
 I see Daire isn't there either so +CC him too.

On 17/08/2022 14:25, Heinrich Schuchardt wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> The "PolarFire SoC MSS Technical Reference Manual" documents the
> following PLIC interrupts:
> 
> 1 - L2 Cache Controller Signals when a metadata correction event occurs
> 2 - L2 Cache Controller Signals when an uncorrectable metadata event occurs
> 3 - L2 Cache Controller Signals when a data correction event occurs
> 4 - L2 Cache Controller Signals when an uncorrectable data event occurs
> 
> This differs from the SiFive FU540 which only has three L2 cache related
> interrupts.
> 
> The sequence in the device tree is defined by an enum:
> 
>     enum {
>             DIR_CORR = 0,
>             DATA_CORR,
>             DATA_UNCORR,
>             DIR_UNCORR,
>     };

Nit: more accurately by the dt-binding:
  interrupts:
    minItems: 3
    items:
      - description: DirError interrupt
      - description: DataError interrupt
      - description: DataFail interrupt
      - description: DirFail interrupt

I do find the names in the enum to be a bit more understandable however,
and ditto for the descriptions in our TRM... Maybe I should put that on
my todo list of cleanups :)


> 
> So the correct sequence of the L2 cache interrupts is
> 
>     interrupts = <1>, <3>, <4>, <2>;

This looks correct to me. You mentioned on IRC that what you were seeing
was a wall of
L2CACHE: DataFail @ 0x00000000.0807FFD8
From a quick look at the driver, what seems to be happening here is that
at some point (possibly before Linux even comes into the picture) there
is an uncorrectable data error. Because the ordering in the dt is wrong,
we read the wrong register and so the interrupt is never actually
cleared. With this patch applied, I see a single DataFail right as the
interrupt gets registed & nothing after that.

I am not really sure what value there is in enabling that driver though,
mostly just seems like a debugging tool & from our pov we would see the
HSS running in the monitor core as being responsible for handling the
l2-cache errors.

@Daire, maybe you have an opinion here?

Patch LGTM, so I'll likely apply it in the next day or two, would just
like to see what Daire has to say first.

> 
> Fixes: e35b07a7df9b ("riscv: dts: microchip: mpfs: Group tuples in interrupt properties")

BTW, it isn't really fixing this patch right? This is a dependency for
backports to 5.15.

Thanks for your patch,
Conor.

> Fixes: 0fa6107eca41 ("RISC-V: Initial DTS for Microchip ICICLE board")
> Cc: Conor Dooley <conor.dooley@microchip.com>
> Cc: stable@vger.kernel.org
> Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
> ---
>  arch/riscv/boot/dts/microchip/mpfs.dtsi | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/riscv/boot/dts/microchip/mpfs.dtsi b/arch/riscv/boot/dts/microchip/mpfs.dtsi
> index 496d3b7642bd..ec1de6344be9 100644
> --- a/arch/riscv/boot/dts/microchip/mpfs.dtsi
> +++ b/arch/riscv/boot/dts/microchip/mpfs.dtsi
> @@ -169,7 +169,7 @@ cctrllr: cache-controller@2010000 {
>                         cache-size = <2097152>;
>                         cache-unified;
>                         interrupt-parent = <&plic>;
> -                       interrupts = <1>, <2>, <3>;
> +                       interrupts = <1>, <3>, <4>, <2>;
>                 };
> 
>                 clint: clint@2000000 {
> --
> 2.36.1
>