On Mon, Sep 08, 2025 at 02:35:29PM GMT, Bjorn Helgaas wrote: > On Wed, Sep 03, 2025 at 12:43:25PM +0530, Manivannan Sadhasivam via B4 Relay wrote: > > As per PCIe spec r6.0, sec 6.6.1, PERST# is an auxiliary signal provided by > > the system to a component as a Fundamental Reset. This signal if available, > > should conform to the rules defined by the electromechanical form factor > > specifications like PCIe CEM spec r4.0, sec 2.2. > > > > Since pwrctrl driver is meant to control the power supplies, it should also > > control the PERST# signal if available. > > Why? Probably obvious to hardware folks, but a sentence about the > necessary connection between power supply and reset would help me. > > > But traditionally, the host bridge > > (controller) drivers are the ones parsing and controlling the PERST# > > signal. They also sometimes need to assert PERST# during their own hardware > > initialization. So it is not possible to move the PERST# control away from > > the controller drivers and it must be shared logically. > > > > Hence, add a new callback 'pci_host_bridge::toggle_perst', that allows the > > pwrctrl core to toggle PERST# with the help of the controller drivers. But > > care must be taken care by the controller drivers to not deassert the > > PERST# signal if this callback is populated. > > > > This callback if available, will be called by the pwrctrl core during the > > device power up and power down scenarios. Controller drivers should > > identify the device using the 'struct device_node' passed during the > > callback and toggle PERST# accordingly. > > "Toggle" isn't my favorite description because it implies that you > don't need to supply the new state; you're just switching from the > current state to the other state, and you wouldn't need to pass a > state. Maybe something like "set_perst" or "set_perst_state" like we > do for set_cpu_online(), *_set_power_state(), etc? > Since the spec mentions the state change as 'assertion' and 'deassertion', how about: pci_host_bridge::perst_assert(struct pci_pwrctrl *pwrctrl, bool assert) - Mani -- மணிவண்ணன் சதாசிவம்
