Re: [PATCH 5/7] ACPI: scan: Add support for deferring adding devices to the second scan phase based on the _DEP list

["Rafael J. Wysocki" <rafael@kernel.org>]

On Sat, Nov 21, 2020 at 9:31 PM Hans de Goede <hdegoede@redhat.com> wrote:
>
> The current solution, of deferring adding of some devices because they
> need access during the OpRegions of other devices while they are added,
> is not very generic.
>
> And support for making the decision to defer adding a device based on
> its _DEP list, instead of the device's HID being in a fixed list of HIDs
> to defer, which should be a more generic way to deal with this.

Thanks a lot for working on this!

I'll have a more thorough look at the series later this week, stay tuned.

> Since this is likely to cause issues on some hardware, this new method will
> only be used if the new acpi.defer_scan_based_on_dep kernel commandline
> option is set to 1.

However, I already can say that I don't like the new command line option.

> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/acpi/scan.c | 45 ++++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 407c8536568b..9927036bfe77 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -31,6 +31,11 @@ extern struct acpi_device *acpi_root;
>
>  #define INVALID_ACPI_HANDLE    ((acpi_handle)empty_zero_page)
>
> +static int defer_scan_based_on_dep = -1;
> +module_param(defer_scan_based_on_dep, int, 0444);
> +MODULE_PARM_DESC(defer_scan_based_on_dep,
> +       "Use new scan-scheme deferring addition of devices with non empty _DEP list (-1=auto, 0=no, 1=yes)");
> +
>  static const char *dummy_hid = "device";
>
>  static LIST_HEAD(acpi_dep_list);
> @@ -1657,11 +1662,45 @@ void acpi_device_add_finalize(struct acpi_device *device)
>
>  static bool acpi_should_defer_add(acpi_handle handle, struct acpi_device_info *info)
>  {
> +       struct acpi_handle_list dep_devices;
> +       acpi_status status;
> +       int i;
> +
>         if (!acpi_check_defer_add || !info)
>                 return false;
>
> -       if (acpi_info_matches_hids(info, acpi_defer_add_hids))
> +       if (!defer_scan_based_on_dep)
> +               return acpi_info_matches_hids(info, acpi_defer_add_hids);
> +
> +       /*
> +        * We check for _ADR here to avoid deferring the adding of the following:
> +        * 1. PCI devices
> +        * 2. ACPI nodes describing USB ports
> +        * Note checking for _ADR catches more then just these cases...

s/then/than/

> +        */
> +       if (info->valid & ACPI_VALID_ADR)
> +               return false;
> +
> +       status = acpi_evaluate_reference(handle, "_DEP", NULL, &dep_devices);
> +       if (ACPI_FAILURE(status))
> +               return false;
> +
> +       for (i = 0; i < dep_devices.count; i++) {
> +               struct acpi_device_info *dep_info;
> +               bool ignore;
> +
> +               status = acpi_get_object_info(dep_devices.handles[i], &dep_info);
> +               if (ACPI_FAILURE(status))
> +                       continue;
> +
> +               ignore = acpi_info_matches_hids(dep_info, acpi_ignore_dep_hids);
> +               kfree(dep_info);
> +
> +               if (ignore)
> +                       continue;
> +
>                 return true;
> +       }
>
>         return false;
>  }
> @@ -2251,6 +2290,10 @@ int __init acpi_scan_init(void)
>         struct acpi_table_stao *stao_ptr;
>         struct acpi_deferred_dev *deferred_dev, *tmp;
>
> +       /* Currently no devices are known which need _dep based scan deferral */
> +       if (defer_scan_based_on_dep == -1)
> +               defer_scan_based_on_dep = 0;
> +
>         acpi_pci_root_init();
>         acpi_pci_link_init();
>         acpi_processor_init();
> --
> 2.28.0
>