linux-kernel - Re: [PATCH v4 01/20] ACPI: PPTT: Use table offset as fw

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Date:   Wed, 22 Jun 2022 13:47:06 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg KH <gregkh@...uxfoundation.org>,
        Atish Patra <atishp@...shpatra.org>,
        Atish Patra <atishp@...osinc.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Qing Wang <wangqing@...o.com>,
        Rob Herring <robh+dt@...nel.org>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Ionela Voinescu <ionela.voinescu@....com>,
        Pierre Gondois <pierre.gondois@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>
Subject: Re: [PATCH v4 01/20] ACPI: PPTT: Use table offset as fw_token instead
 of virtual address

On Tue, Jun 21, 2022 at 9:20 PM Sudeep Holla <sudeep.holla@....com> wrote:
>
> There is need to use the cache sharing information quite early during
> the boot before the secondary cores are up and running. The permanent
> memory map for all the ACPI tables(via acpi_permanent_mmap) is turned
> on in acpi_early_init() which is quite late for the above requirement.
>
> As a result there is possibility that the ACPI PPTT gets mapped to
> different virtual addresses. In such scenarios, using virtual address as
> fw_token before the acpi_permanent_mmap is enabled results in different
> fw_token for the same cache entity and hence wrong cache sharing
> information will be deduced based on the same.
>
> Instead of using virtual address, just use the table offset as the
> unique firmware token for the caches. The same offset is used as
> ACPI identifiers if the firmware has not set a valid one for other
> entries in the ACPI PPTT.
>
> Cc: linux-acpi@...r.kernel.org
> Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> ---
>  drivers/acpi/pptt.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> Hi Rafael,
>
> If you are happy with this change, can you provide Ack, so that it can be
> merged together with other changes ?

No objections:

Acked-by: Rafael J. Wysocki <rafael@...nel.org>

> diff --git a/drivers/acpi/pptt.c b/drivers/acpi/pptt.c
> index 701f61c01359..763f021d45e6 100644
> --- a/drivers/acpi/pptt.c
> +++ b/drivers/acpi/pptt.c
> @@ -437,7 +437,8 @@ static void cache_setup_acpi_cpu(struct acpi_table_header *table,
>                 pr_debug("found = %p %p\n", found_cache, cpu_node);
>                 if (found_cache)
>                         update_cache_properties(this_leaf, found_cache,
> -                                               cpu_node, table->revision);
> +                                               ACPI_TO_POINTER(ACPI_PTR_DIFF(cpu_node, table)),
> +                                               table->revision);
>
>                 index++;
>         }
> --
> 2.36.1
>