Re: [PATCH v14 4/9] acpi/arm64: Add GTDT table parse driver

[Fu Wei]

Hi Mark,

On 21 October 2016 at 00:37, Mark Rutland <mark.rutland@xxxxxxx> wrote:
> Hi,
>
> As a heads-up, on v4.9-rc1 I see conflicts at least against
> arch/arm64/Kconfig. Luckily git am -3 seems to be able to fix that up
> automatically, but this will need to be rebased before the next posting
> and/or merging.
>
> On Thu, Sep 29, 2016 at 02:17:12AM +0800, fu.wei@xxxxxxxxxx wrote:
>> +static int __init map_gt_gsi(u32 interrupt, u32 flags)
>> +{
>> +     int trigger, polarity;
>> +
>> +     if (!interrupt)
>> +             return 0;
>
> Urgh.
>
> Only the secure interrupt (which we do not need) is optional in this
> manner, and (hilariously), zero appears to also be a valid GSIV, per
> figure 5-24 in the ACPI 6.1 spec.
>
> So, I think that:
>
> (a) we should not bother parsing the secure interrupt

If I understand correctly, from this point of view, kernel don't
handle the secure interrupt.
But the current arm_arch_timer driver still enable/disable/request
PHYS_SECURE_PPI
with PHYS_NONSECURE_PPI.
That means we still need to parse the secure interrupt.
Please correct me, if I misunderstand something? :-)

> (b) we should drop the check above

yes, if zero is a valid GSIV, this makes sense.

> (c) we should report the spec issue to the ASWG
>
>> +/*
>> + * acpi_gtdt_c3stop - got c3stop info from GTDT
>> + *
>> + * Returns 1 if the timer is powered in deep idle state, 0 otherwise.
>> + */
>> +bool __init acpi_gtdt_c3stop(void)
>> +{
>> +     struct acpi_table_gtdt *gtdt = acpi_gtdt_desc.gtdt;
>> +
>> +     return !(gtdt->non_secure_el1_flags & ACPI_GTDT_ALWAYS_ON);
>> +}
>
> It looks like this can differ per interrupt. Shouldn't we check the
> appropriate one?

yes, I think you are right.

>
>> +int __init acpi_gtdt_init(struct acpi_table_header *table)
>> +{
>> +     void *start;
>> +     struct acpi_table_gtdt *gtdt;
>> +
>> +     gtdt = container_of(table, struct acpi_table_gtdt, header);
>> +
>> +     acpi_gtdt_desc.gtdt = gtdt;
>> +     acpi_gtdt_desc.gtdt_end = (void *)table + table->length;
>> +
>> +     if (table->revision < 2) {
>> +             pr_debug("Revision:%d doesn't support Platform Timers.\n",
>> +                      table->revision);
>> +             return 0;
>> +     }
>> +
>> +     if (!gtdt->platform_timer_count) {
>> +             pr_debug("No Platform Timer.\n");
>> +             return 0;
>> +     }
>> +
>> +     start = (void *)gtdt + gtdt->platform_timer_offset;
>> +     if (start < (void *)table + sizeof(struct acpi_table_gtdt)) {
>> +             pr_err(FW_BUG "Failed to retrieve timer info from firmware: invalid data.\n");
>> +             return -EINVAL;
>> +     }
>> +     acpi_gtdt_desc.platform_timer_start = start;
>> +
>> +     return gtdt->platform_timer_count;
>> +}
>
> This is never used as anything other than a status code.
>
> Just return zero; we haven't parsed the platform timers themselves at
> this point anyway.

Sorry, in my driver, I use this return value to inform driver

 negative number : error
0 : we don't have platform timer in GTDT table.
positive number: the number of platform timer we have in GTDT table.

please correct me, if I am doing it in wrong way. Thanks :-)


>
> Thanks,
> Mark.



-- 
Best regards,

Fu Wei
Software Engineer
Red Hat