Device Specific Method PCIe SSD Status LED Management (_DSM) defined in
PCI Firmware Spec r3.3 sec 4.7 provides a way to manage LEDs via ACPI.
The design is similar to NPEM defined in PCIe Base Specification r6.1
sec 6.28:
- both standards are indication oriented,
- _DSM supported bits are corresponding to NPEM capability
register bits
- _DSM control bits are corresponding to NPEM control register
bits.
_DSM does not support enclosure specific indications and special NPEM
commands NPEM_ENABLE and NPEM_RESET.
_DSM is implemented as a second op in NPEM driver. The standard used
in background is logged with info priority. The interface is accessed
same as NPEM.
According to spec, _DSM has higher priority and availability of _DSM
in not limited to devices with NPEM support. It is followed in
implementation.
DELL implementation of DSM is using acpi ipmi, which is not available
imediatelly (in fact it tooks up to 10s for this interface
to be avialable). It can determine if DSM is supported
(GET_SUPPORTED_STATES_DSM is working) but it cannot serve GET_STATE_DSM
or SET_STATE_DSM commands in this time.
