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67211aadcb
Add a mechanism to identify standard PCIe regulators in the DT, allocate
them, and turn them on before the rest of the bus is scanned during
pci_host_probe().
The allocated structure that contains the regulators is stored in the port
driver dev.driver_data field. Here is a point-by-point of how and when
this mechanism is activated:
If:
-- PCIe RC driver sets pci_ops {add,remove)_bus to
pci_subdev_regulators_{add,remove}_bus during its probe.
-- There is a DT node "RB" under the host bridge DT node.
-- During the RC driver's pci_host_probe() the add_bus callback
is invoked where (bus->parent && pci_is_root_bus(bus->parent)
is true
Then:
-- A struct subdev_regulators structure will be allocated and
assigned to bus->dev.driver_data.
-- regulator_bulk_{get,enable} will be invoked on &bus->dev
and the former will search for and process any
vpcie{12v,3v3,3v3aux}-supply properties that reside in node "RB".
-- The regulators will be turned off/on for any unbind/bind operations.
-- The regulators will be turned off/on for any suspend/resumes, but
only if the RC driver handles this on its own. This will appear
in a later commit for the pcie-brcmstb.c driver.
The unabridged reason for doing this is as follows. We would like the
Broadcom STB PCIe root complex driver (and others) to be able to turn
off/on regulators[1] that provide power to endpoint[2] devices. Typically,
the drivers of these endpoint devices are stock Linux drivers that are not
aware that these regulator(s) exist and must be turned on for the driver to
be probed. The simple solution of course is to turn these regulators on at
boot and keep them on. However, this solution does not satisfy at least
three of our usage modes:
1. For example, one customer uses multiple PCIe controllers, but wants
the ability to, by script invoking and unbind, turn any or all of them
and their subdevices off to save power, e.g. when in battery mode.
2. Another example is when a watchdog script discovers that an endpoint
device is in an unresponsive state and would like to unbind, power
toggle, and re-bind just the PCIe endpoint and controller.
3. Of course we also want power turned off during suspend mode. However,
some endpoint devices may be able to "wake" during suspend and we need
to recognise this case and veto the nominal act of turning off its
regulator. Such is the case with Wake-on-LAN and Wake-on-WLAN support
where the PCIe endpoint device needs to be kept powered on in order to
receive network packets and wake the system.
In all of these cases it is advantageous for the PCIe controller to govern
the turning off/on the regulators needed by the endpoint device. The first
two cases can be done by simply unbinding and binding the PCIe controller,
if the controller has control of these regulators.
[1] These regulators typically govern the actual power supply to the
endpoint chip. Sometimes they may be the official PCIe socket
power -- such as 3.3v or aux-3.3v. Sometimes they are truly
the regulator(s) that supply power to the EP chip.
[2] The 99% configuration of our boards is a single endpoint device
attached to the PCIe controller. I use the term endpoint but it could
possibly mean a switch as well.
Link: https://lore.kernel.org/r/20220106160332.2143-6-jim2101024@gmail.com
Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
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Linux kernel
============
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In order to build the documentation, use ``make htmldocs`` or
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There are various text files in the Documentation/ subdirectory,
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