Re: [PATCH v1 3/6] PCI: brcmstb: Fix potential premature regluator disabling

On Thu, Feb 6, 2025 at 12:33 PM Bjorn Helgaas [off-list ref] wrote:

In subject,

s/regluator/regulator/

ack

On Wed, Feb 05, 2025 at 02:12:03PM -0500, Jim Quinlan wrote:

quoted

Our system for enabling and disabling regulators is designed to work
only on the port driver below the root complex.  The conditions to
discriminate for this case should be the same when we are adding or
removing the bus.  Without this change the regulators may be disabled
prematurely when a bus further down the tree is removed.

What did the user do to cause the bus to be removed?  I'm wondering if
we turn off the power while the link is still up.  If we do, how does
it get turned back on?  Does that require a manual rescan, and the
scan of the child bus gets the power turned back on?

Hi Bjorn,

We only support having a regulator  for the device immediately
connected to the RC.  If the entire RC driver is unbound or rmod'd for
example, a device further down in the tree would be dismantled first
and it would turn off the regulator for the device closest to the RC.
This could cause errors during the removal of the closest device, as
it would be unable to access its registers.

Note that we do not support hotplug so there are no rescans going on
in our world.  We do have customers whose chip has several PCIe
controllers and they do unbind some of their drivers during power
critical scenarios.

The RPi folks do not use this regulator mechanism AFAICT.

Regards,
Jim Quiinlan
Broadcom STB/CM

quoted

Fixes: 9e6be018b263 ("PCI: brcmstb: Enable child bus device regulators from DT")
Signed-off-by: Jim Quinlan <redacted>
---
 drivers/pci/controller/pcie-brcmstb.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
index bf919467cbcd..4f5d751cbdd7 100644
--- a/drivers/pci/controller/pcie-brcmstb.c
+++ b/drivers/pci/controller/pcie-brcmstb.c

@@ -1441,7 +1441,7 @@ static void brcm_pcie_remove_bus(struct pci_bus *bus)
      struct subdev_regulators *sr = pcie->sr;
      struct device *dev = &bus->dev;

-     if (!sr)
+     if (!sr || !bus->parent || !pci_is_root_bus(bus->parent))
              return;

      if (regulator_bulk_disable(sr->num_supplies, sr->supplies))
--

2.43.0