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

Hi Mark,

On 21 October 2016 at 00:37, Mark Rutland [off-list ref] 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 at linaro.org wrote:

quoted

+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

quoted

+/*
+ * 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.

quoted

+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