Re: [RFC PATCH 05/25] hw/cxl/device: Implement the CAP array (8.2.8.1-2)

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Tue, 10 Nov 2020 21:47:04 -0800
Ben Widawsky <ben.widawsky@intel.com> wrote:

> This implements all device MMIO up to the first capability .That
> includes the CXL Device Capabilities Array Register, as well as all of
> the CXL Device Capability Header Registers. The latter are filled in as
> they are implemented in the following patches.
> 
> Signed-off-by: Ben Widawsky <ben.widawsky@intel.com>

Question below.

Thanks,

Jonathan

> ---
>  hw/cxl/cxl-device-utils.c | 73 +++++++++++++++++++++++++++++++++++++++
>  hw/cxl/meson.build        |  1 +
>  2 files changed, 74 insertions(+)
> 
> diff --git a/hw/cxl/cxl-device-utils.c b/hw/cxl/cxl-device-utils.c
> index e69de29bb2..a391bb15c6 100644
> --- a/hw/cxl/cxl-device-utils.c
> +++ b/hw/cxl/cxl-device-utils.c
> @@ -0,0 +1,73 @@
> +/*
> + * CXL Utility library for devices
> + *
> + * Copyright(C) 2020 Intel Corporation.
> + *
> + * This work is licensed under the terms of the GNU GPL, version 2. See the
> + * COPYING file in the top-level directory.
> + */
> +
> +#include "qemu/osdep.h"
> +#include "qemu/log.h"
> +#include "hw/cxl/cxl.h"
> +
> +static uint64_t caps_reg_read(void *opaque, hwaddr offset, unsigned size)
> +{
> +    CXLDeviceState *cxl_dstate = opaque;
> +
> +    switch (size) {
> +    case 4:
> +        if (unlikely(offset & (sizeof(uint32_t) - 1))) {
> +            qemu_log_mask(LOG_UNIMP, "Unaligned register read\n");
> +            return 0;
> +        }
> +        break;
> +    case 8:
> +        if (unlikely(offset & (sizeof(uint64_t) - 1))) {
> +            qemu_log_mask(LOG_UNIMP, "Unaligned register read\n");
> +            return 0;
> +        }
> +        break;

Seems unlikely but in theory we might get other sizes such as 2 and need
that to be aligned?

If we just don't want to support them perhaps a default with suitable error
print is appropriate?

> +    }
> +
> +    return ldn_le_p(cxl_dstate->caps_reg_state + offset, size);
> +}
> +
> +static const MemoryRegionOps caps_ops = {
> +    .read = caps_reg_read,
> +    .write = NULL,
> +    .endianness = DEVICE_LITTLE_ENDIAN,
> +    .valid = {
> +        .min_access_size = 4,
> +        .max_access_size = 8,
> +    },
> +    .impl = {
> +        .min_access_size = 4,
> +        .max_access_size = 8,
> +    },
> +};
> +
> +void cxl_device_register_block_init(Object *obj, CXLDeviceState *cxl_dstate)
> +{
> +    /* This will be a BAR, so needs to be rounded up to pow2 for PCI spec */
> +    memory_region_init(
> +        &cxl_dstate->device_registers, obj, "device-registers",
> +        pow2ceil(CXL_MAILBOX_REGISTERS_LENGTH + CXL_MAILBOX_REGISTERS_OFFSET));
> +
> +    memory_region_init_io(&cxl_dstate->caps, obj, &caps_ops, cxl_dstate,
> +                          "cap-array", CXL_DEVICE_REGISTERS_OFFSET - 0);
> +
> +    memory_region_add_subregion(&cxl_dstate->device_registers, 0,
> +                                &cxl_dstate->caps);
> +}
> +
> +void cxl_device_register_init_common(CXLDeviceState *cxl_dstate)
> +{
> +    uint32_t *cap_hdrs = cxl_dstate->caps_reg_state32;
> +    const int cap_count = 0;
> +
> +    /* CXL Device Capabilities Array Register */
> +    ARRAY_FIELD_DP32(cap_hdrs, CXL_DEV_CAP_ARRAY, CAP_ID, 0);
> +    ARRAY_FIELD_DP32(cap_hdrs, CXL_DEV_CAP_ARRAY, CAP_VERSION, 1);
> +    ARRAY_FIELD_DP32(cap_hdrs, CXL_DEV_CAP_ARRAY2, CAP_COUNT, cap_count);
> +}
> diff --git a/hw/cxl/meson.build b/hw/cxl/meson.build
> index 00c3876a0f..47154d6850 100644
> --- a/hw/cxl/meson.build
> +++ b/hw/cxl/meson.build
> @@ -1,3 +1,4 @@
>  softmmu_ss.add(when: 'CONFIG_CXL', if_true: files(
>    'cxl-component-utils.c',
> +  'cxl-device-utils.c',
>  ))