Re: [PATCH v2 10/16] xen/riscv: imsic_init() implementation

[Jan Beulich <jbeulich@xxxxxxxx>]

On 19.05.2025 17:19, Oleksii Kurochko wrote:
> On 5/15/25 10:42 AM, Jan Beulich wrote:
>> On 06.05.2025 18:51, Oleksii Kurochko wrote:
>>> --- /dev/null
>>> +++ b/xen/arch/riscv/include/asm/imsic.h
>>> @@ -0,0 +1,65 @@
>>> +/* SPDX-License-Identifier: MIT */
>>> +
>>> +/*
>>> + * xen/arch/riscv/imsic.h
>>> + *
>>> + * RISC-V Incoming MSI Controller support
>>> + *
>>> + * (c) 2023 Microchip Technology Inc.
>>> + */
>>> +
>>> +#ifndef ASM__RISCV__IMSIC_H
>>> +#define ASM__RISCV__IMSIC_H
>>> +
>>> +#include <xen/types.h>
>>> +
>>> +#define IMSIC_MMIO_PAGE_SHIFT   12
>>> +#define IMSIC_MMIO_PAGE_SZ      (1UL << IMSIC_MMIO_PAGE_SHIFT)
>>> +
>>> +#define IMSIC_MIN_ID            63
>> This isn't the "minimum ID", but the "minimum permissible number of IDs" as 
>> per
>> its first use in imsic_parse_node(). Further uses there consider it a mask,
>> which makes me wonder whether the imsic_cfg.nr_ids field name is actually
>> correct: Isn't this the maximum valid ID rather than their count/number?
> 
> imsic_cfg.nr_ids it is a value of interrupt identities supported by IMSIC 
> interrupt file according to
> DT binding:
>    riscv,num-ids:
>      $ref: /schemas/types.yaml#/definitions/uint32
>      minimum: 63
>      maximum: 2047
>      description:
>        Number of interrupt identities supported by IMSIC interrupt file.

Unless this count accounts for 0 being invalid (and hence isn't counted), I'm
still confused: With the maximum value this would mean 2046 is still valid,
but 2047 isn't anymore. When normally such a boundary would be at an exact
power of 2, i.e. between 2047 and 2048 here.

Jan