Re: [RFC PATCH v3 1/2] dt-bindings: cache: r9a07g043f-l2-cache: Add DT binding documentation for L2 cache controller

[Lad, Prabhakar]

Hi Geert,

Thank you for the review.

On Mon, Oct 24, 2022 at 2:47 PM Geert Uytterhoeven <geert@xxxxxxxxxxxxxx> wrote:
>
> Hi Prabhakar,
>
> On Thu, Oct 20, 2022 at 12:02 AM Prabhakar <prabhakar.csengg@xxxxxxxxx> wrote:
> > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> >
> > Add DT binding documentation for L2 cache controller found on RZ/Five SoC.
> >
> > The Renesas RZ/Five microprocessor includes a RISC-V CPU Core (AX45MP
> > Single) from Andes. The AX45MP core has an L2 cache controller, this patch
> > describes the L2 cache block.
> >
> > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
>
> Thanks for your patch!
>
> > --- /dev/null
> > +++ b/Documentation/devicetree/bindings/cache/andestech,ax45mp-cache.yaml
> > @@ -0,0 +1,125 @@
> > +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
> > +# Copyright (C) 2022 Renesas Electronics Corp.
> > +%YAML 1.2
> > +---
> > +$id: http://devicetree.org/schemas/cache/andestech,ax45mp-cache.yaml#
> > +$schema: http://devicetree.org/meta-schemas/core.yaml#
> > +
> > +title: Andestech AX45MP L2 Cache Controller
> > +
> > +maintainers:
> > +  - Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
> > +
> > +description:
> > +  A level-2 cache (L2C) is used to improve the system performance by providing
> > +  a larger amount of cache line entries and reasonable access delays. The L2C
>
> large
>
OK.

> > +  is shared between cores, and a non-inclusive non-exclusive policy is used.
> > +
> > +select:
> > +  properties:
> > +    compatible:
> > +      contains:
> > +        enum:
> > +          - andestech,ax45mp-cache
> > +
> > +  required:
> > +    - compatible
> > +
> > +properties:
> > +  compatible:
> > +    items:
> > +      - const: andestech,ax45mp-cache
> > +      - const: cache
> > +
> > +  reg:
> > +    maxItems: 1
> > +
> > +  interrupts:
> > +    maxItems: 1
> > +
> > +  cache-line-size:
> > +    const: 64
>
> This is fixed here, but the driver accepts (and uses) whatever value specified?
>
Right, I'll add a check in the driver.

> > +
> > +  cache-level:
> > +    const: 2
> > +
> > +  cache-sets:
> > +    const: 1024
> > +
> > +  cache-size:
> > +    enum: [131072, 262144, 524288, 1048576, 2097152]
> > +
> > +  cache-unified: true
> > +
> > +  next-level-cache: true
> > +
> > +  andestech,pma-regions:
> > +    $ref: /schemas/types.yaml#/definitions/uint32-matrix
> > +    minItems: 1
> > +    maxItems: 16
> > +    description: Optional array of memory regions to be set as non-cacheable
> > +                 bufferable regions which will be setup in the PMA.
> > +
> > +  andestech,inst-prefetch:
> > +    description: Instruction prefetch depth
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [ 0, 1, 2, 3 ]
> > +
> > +  andestech,data-prefetch:
> > +    description: Data prefetch depth
> > +    $ref: /schemas/types.yaml#/definitions/uint32
> > +    enum: [ 0, 1, 2, 3 ]
>
> According to Section 8.1.2 ("L2-Cache Prefetch"), this should be
> [ 0, 2, 4, 8 ].
>
I was directly fetching the value, but as you pointed out I'll switch
to the request count and convert the value accordingly in the driver.

> > +  andestech,tag-ram-ctl:
> > +    description: Tag RAM output cycle. First tuple indicates output cycle and the
> > +      second tuple indicates setup cycle.
>
> Nit: to me it sounds more logical to have the setup cycle first.
> See also the order in the comment in the driver code:
>
>      /* tag RAM and data RAM setup and output cycle */
>
> > +    $ref: /schemas/types.yaml#/definitions/uint8-array
> > +    items:
> > +      - minimum: 0
> > +        maximum: 2
> > +      - minimum: 0
> > +        maximum: 2
> > +
> > +  andestech,data-ram-ctl:
> > +    description: Data RAM output cycle. First tuple indicates output cycle and the
> > +      second tuple indicates setup cycle.
>
> Likewise.
>
> > +    $ref: /schemas/types.yaml#/definitions/uint8-array
> > +    items:
> > +      - minimum: 0
> > +        maximum: 2
> > +      - minimum: 0
> > +        maximum: 2
>
> Do we really need these andestech-specific properties?
> If yes, how much (if any) of this do we want to be handled by the boot
> loader, and how much (if any) by Linux?
> If Linux is responsible, we might have to boot with L2 disabled, right?
>
> For ARM Cortex A15/A7, we also have arm,{data,tag}-latency properties
> defined, but no DTS specifies them (my patches to add them on R-Car
> Gen2 were rejected).  Note that this is different for e.g. older PL310.
>
OK, I think we can get rid of the below properties completely from
here and have them configured earlier (ie in u-boot).

       -   andestech,inst-prefetch
       -   andestech,data-prefetch
       -   andestech,tag-ram-ctl
       -   andestech,data-ram-ctl

Cheers,
Prabhakar