[PATCH 7/9] PCI: hotplug: Drop hotplug_slot_info

[Rafael J. Wysocki]

On Sun, Aug 19, 2018 at 4:43 PM Lukas Wunner <lukas at wunner.de> wrote:
>
> Ever since the PCI hotplug core was introduced in 2002, drivers had to
> allocate and register a struct hotplug_slot_info for every slot:
> https://git.kernel.org/tglx/history/c/a8a2069f432c
>
> Apparently the idea was that drivers furnish the hotplug core with an
> up-to-date card presence status, power status, latch status and
> attention indicator status as well as notify the hotplug core of changes
> thereof.  However only 4 out of 12 hotplug drivers bother to notify the
> hotplug core with pci_hp_change_slot_info() and the hotplug core never
> made any use of the information:  There is just a single macro in
> pci_hotplug_core.c, GET_STATUS(), which uses the hotplug_slot_info if
> the driver lacks the corresponding callback in hotplug_slot_ops.  The
> macro is called when the user reads the attribute via sysfs.
>
> Now, if the callback isn't defined, the attribute isn't exposed in sysfs
> in the first place (see e.g. has_power_file()).  There are only two
> situations when the hotplug_slot_info would actually be accessed:
>
> * If the driver defines ->enable_slot or ->disable_slot but not
>   ->get_power_status.
>
> * If the driver defines ->set_attention_status but not
>   ->get_attention_status.
>
> There is no driver doing the former and just a single driver doing the
> latter, namely pnv_php.c.  Amend it with a ->get_attention_status
> callback.  With that, the hotplug_slot_info becomes completely unused by
> the PCI hotplug core.  But a few drivers use it internally as a cache:
>
> cpcihp uses it to cache the latch_status and adapter_status.
> cpqhp uses it to cache the adapter_status.
> pnv_php and rpaphp use it to cache the attention_status.
> shpchp uses it to cache all four values.
>
> Amend these drivers to cache the information in their private slot
> struct.  shpchp's slot struct already contains members to cache the
> power_status and adapter_status, so additional members are only needed
> for the other two values.  In the case of cpqphp, the cached value is
> only accessed in a single place, so instead of caching it, read the
> current value from the hardware.
>
> Caution:  acpiphp, cpci, cpqhp, shpchp, asus-wmi and eeepc-laptop
> populate the hotplug_slot_info with initial values on probe.  That code
> is herewith removed.  There is a theoretical chance that the code has
> side effects without which the driver fails to function, e.g. if the
> ACPI method to read the adapter status needs to be executed at least
> once on probe.  That seems unlikely to me, still maintainers should
> review the changes carefully for this possibility.

I'm not aware of any case in which it will break anything, so

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki at intel.com>

but if that happens, it may be necessary to add the execution of the
control methods in question directly to the initialization part.