Re: [PATCH v2 05/18] ARM64 / ACPI: Parse FADT table to get PSCI flags for PSCI init

[Sudeep Holla]

On 19/08/14 11:39, Hanjun Guo wrote:
> On 2014-8-19 2:32, Sudeep Holla wrote:
> > On 04/08/14 16:28, Hanjun Guo wrote:
> > > There are two flags: PSCI_COMPLIANT and PSCI_USE_HVC. When set,
> > > the former signals to the OS that the hardware is PSCI compliant.
> > > The latter selects the appropriate conduit for PSCI calls by
> > > toggling between Hypervisor Calls (HVC) and Secure Monitor Calls
> > > (SMC).
> > >
> > > FADT table contains such information, parse FADT to get the flags
> > > for PSCI init. Since ACPI 5.1 doesn't support self defined PSCI
> > > function IDs, which means that only PSCI 0.2+ is supported in ACPI.
> > >
> > > At the same time, only ACPI 5.1 or higher verison supports PSCI,
> > > and FADT Major.Minor version was introduced in ACPI 5.1, so we
> > > will check the version and only parse FADT table with version >= 5.1.
> > >
> > > If firmware provides ACPI tables with ACPI version less than 5.1,
> > > OS will be messed up with those information and have no way to
> > > bring up secondery CPUs, so disable ACPI if we get an FADT table
> > > with version less that 5.1.
> [...]
> > > +static int __init acpi_parse_fadt(struct acpi_table_header *table)
> > > +{
> > > +    struct acpi_table_fadt *fadt = (struct acpi_table_fadt *)table;
> > > +
> > > +    /*
> > > +     * Revision in table header is the FADT Major version,
> > > +     * and there is a minor version of FADT which was introduced
> > > +     * by ACPI 5.1, we only deal with ACPI 5.1 or higher version
> > > +     * to get arm boot flags, or we will disable ACPI.
> > > +     */
> > > +    if (table->revision < 5 || fadt->minor_revision < 1) {
> >
> >                  &&
>
> Catalin also pointed out this bug :), but && is not enough, for example,
> this would not trigger of revision 4.1, although 4.1 is not exist, but
> the code will still confusing people, so I updated the code as:

Right I missed it :), the below code looks fine.

> +       if (table->revision > 5 ||
> +           (table->revision == 5 && fadt->minor_revision >= 1)) {
> +               return 0;
> +       } else {
> +               pr_info("FADT revision is %d.%d, no PSCI support, should be 5.1
> or higher\n",
> +                       table->revision, fadt->minor_revision);
> +               disable_acpi();

As suggested elsewhere try to eliminate this and have it once if
acpi_boot_init failed for any reasons.

Regards,
Sudeep

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