Currently almost each platform driver uses its own resets and clocks
naming in order to get the corresponding descriptors. It makes the code
harder to maintain and comprehend especially seeing the DWC PCIe core main
resets and clocks signals set hasn't changed much for about at least one
major IP-core release. So in order to organize things around these signals
we suggest to create a generic interface for them in accordance with the
naming introduced in the DWC PCIe IP-core reference manual:

Application clocks:
- "dbi"  - data bus interface clock (on some DWC PCIe platforms it's
           referred as "pclk", "pcie", "sys", "ahb", "cfg", "iface",
           "gio", "reg", "pcie_apb_sys");
- "mstr" - AXI-bus master interface clock (some DWC PCIe glue drivers
           refer to this clock as "port", "bus", "pcie_bus",
           "bus_master/master_bus/axi_m", "pcie_aclk");
- "slv"  - AXI-bus slave interface clock (also called as "port", "bus",
           "pcie_bus", "bus_slave/slave_bus/axi_s", "pcie_aclk",
           "pcie_inbound_axi").

Core clocks:
- "pipe" - core-PCS PIPE interface clock coming from external PHY (it's
           normally named by the platform drivers as just "pipe");
- "core" - primary clock of the controller (none of the platform drivers
           declare such a clock but in accordance with the ref. manual
           the devices may have it separately specified);
- "aux"  - auxiliary PMC domain clock (it is named by some platforms as
           "pcie_aux" and just "aux");
- "ref"  - Generic reference clock (it is a generic clock source, which
           can be used as a signal source for multiple interfaces, some
           platforms call it as "ref", "general", "pcie_phy",
           "pcie_phy_ref").

Application resets:
- "dbi"  - Data-bus interface reset (it's CSR interface clock and is
           normally called as "apb" though technically it's not APB but
           DWC PCIe-specific interface);
- "mstr" - AXI-bus master reset (some platforms call it as "port", "apps",
           "bus", "axi_m");
- "slv"  - ABI-bus slave reset (some platforms call it as "port", "apps",
           "bus", "axi_s").

Core resets:
- "non-sticky" - non-sticky CSR flags reset;
- "sticky"     - sticky CSR flags reset;
- "pipe"       - PIPE-interface (Core-PCS) logic reset (some platforms
                 call it just "pipe");
- "core"       - controller primary reset (resets everything except PMC
                 module, some platforms refer to this signal as "soft",
                 "pci");
- "phy"        - PCS/PHY block reset (strictly speaking it is normally
                 connected to the input of an external block, but the
                 reference manual says it must be available for the PMC
                 working correctly, some existing platforms call it
                 "pciephy", "phy", "link");
- "hot"        - PMC hot reset signal (also called as "sleep");
- "pwr"        - cold reset signal (can be referred as "pwr", "turnoff").

Bus reset:
- "perst" - PCIe standard signal used to reset the PCIe peripheral
            devices.

As you can see each platform uses it's own naming for basically the same
set of the signals. In the framework of this commit we suggest to add a
set of the clocks and reset signals resources, corresponding names and
identifiers for each denoted entity. At current stage the platforms will
be able to use the provided infrastructure to automatically request all
these resources and manipulate with them in the Host/EP init callbacks.
Alas it isn't that easy to create a common cold/hot reset procedure due to
too many platform-specifics in the procedure, like the external flags
exposure and the delays requirement.

Link: https://lore.kernel.org/r/20221113191301.5526-20-Sergey.Semin@baikalelectronics.ruSigned-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Lorenzo Pieralisi <lpieralisi@kernel.org>