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

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Date:   Mon, 27 Jun 2022 14:41:54 +0100
From:   Ionela Voinescu <ionela.voinescu@....com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     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>,
        Pierre Gondois <pierre.gondois@....com>,
        linux-arm-kernel@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v4 01/20] ACPI: PPTT: Use table offset as fw_token
 instead of virtual address

Hi Sudeep,

On Tuesday 21 Jun 2022 at 20:20:15 (+0100), Sudeep Holla 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 ?
> 
> Regards,
> Sudeep
> 
> 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
> 

I've run the set on Kunpeng920 where Dietmar noticed an issue [1] before
and it looks good to me.

Tested-by: Ionela Voinescu <ionela.voinescu@....com>

[1]
https://lore.kernel.org/lkml/0bf199a0-251d-323c-974a-bfd4e26f4cce@arm.com/

Thanks,
Ionela.