linux-kernel - Re: [PATCH RFC 2/2] soc: Add a basic ACPI generic driver

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Date:   Tue, 28 Jan 2020 15:20:40 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     John Garry <john.garry@...wei.com>
Cc:     rjw@...ysocki.net, lenb@...nel.org, jeremy.linton@....com,
        arnd@...db.de, olof@...om.net, linux-kernel@...r.kernel.org,
        linux-acpi@...r.kernel.org, guohanjun@...wei.com,
        gregkh@...uxfoundation.org, Sudeep Holla <sudeep.holla@....com>
Subject: Re: [PATCH RFC 2/2] soc: Add a basic ACPI generic driver

(commenting on other parts though I am not sure if we want to add this
despite it being deprecated)

On Tue, Jan 28, 2020 at 07:14:19PM +0800, John Garry wrote:
> Add a generic driver for platforms which populate their ACPI PPTT
> processor package ID Type Structure according to suggestion in the ACPI
> spec - see ACPI 6.2, section 5.2.29.3 ID structure Type 2.
>
> The soc_id is from member LEVEL_2_ID.
>
> For this, we need to use a whitelist of platforms which are known to
> populate the structure as suggested.
>
> For now, only the vendor and soc_id fields are exposed.
>
> Signed-off-by: John Garry <john.garry@...wei.com>
> ---
>  drivers/soc/Makefile       |   1 +
>  drivers/soc/acpi_generic.c | 102 +++++++++++++++++++++++++++++++++++++
>  2 files changed, 103 insertions(+)
>  create mode 100644 drivers/soc/acpi_generic.c
>
> diff --git a/drivers/soc/Makefile b/drivers/soc/Makefile
> index 8b49d782a1ab..2a59a30a22cd 100644
> --- a/drivers/soc/Makefile
> +++ b/drivers/soc/Makefile
> @@ -3,6 +3,7 @@
>  # Makefile for the Linux Kernel SOC specific device drivers.
>  #
>
> +obj-$(CONFIG_ACPI_PPTT)		+= acpi_generic.o
>  obj-$(CONFIG_ARCH_ACTIONS)	+= actions/
>  obj-$(CONFIG_SOC_ASPEED)	+= aspeed/
>  obj-$(CONFIG_ARCH_AT91)		+= atmel/
> diff --git a/drivers/soc/acpi_generic.c b/drivers/soc/acpi_generic.c
> new file mode 100644
> index 000000000000..34a1f5f8e063
> --- /dev/null
> +++ b/drivers/soc/acpi_generic.c
> @@ -0,0 +1,102 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) John Garry, john.garry@...wei.com
> + */
> +
> +#define pr_fmt(fmt) "SOC ACPI GENERIC: " fmt
> +
> +#include <linux/acpi.h>
> +#include <linux/sys_soc.h>
> +
> +/*
> + * Known platforms that fill in PPTT package ID structures according to
> + * ACPI spec examples, that being:
> + * - Custom driver attribute is in ID Type Structure VENDOR_ID member
> + * - SoC id is in ID Type Structure LEVEL_2_ID member
> + *    See ACPI SPEC 6.2 Table 5-154 for PPTT ID Type Structure
> + */
> +static struct acpi_platform_list plat_list[] = {
> +	{"HISI  ", "HIP08   ", 0, ACPI_SIG_PPTT, all_versions},

What do you want to match this ? The same silicon can end up with
different OEMs and this list just blows up soon for single SoC if
used by different OEM/ODMs. I assume we get all the required info
from the Type 2 table entry and hence can just rely on that. If
PPTT has type 2 entry, just initialise this soc driver and expose
the relevant information from the table entry.

--
Regards,
Sudeep