linux-kernel - Re: [PATCH v1 2/6] PCI: brcmstb: Fix error path upon call of regulator_bulk

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Message-ID: <CA+-6iNxz-==Ws-EZTBbSzqmEApAX=bsq9=x=3=Z9G3kqxD53Hg@mail.gmail.com>
Date: Thu, 6 Feb 2025 14:39:44 -0500
From: Jim Quinlan <james.quinlan@...adcom.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: linux-pci@...r.kernel.org, Nicolas Saenz Julienne <nsaenz@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Lorenzo Pieralisi <lorenzo.pieralisi@....com>, 
	Cyril Brulebois <kibi@...ian.org>, Stanimir Varbanov <svarbanov@...e.de>, 
	bcm-kernel-feedback-list@...adcom.com, jim2101024@...il.com, 
	Florian Fainelli <florian.fainelli@...adcom.com>, Lorenzo Pieralisi <lpieralisi@...nel.org>, 
	Krzysztof Wilczyński <kw@...ux.com>, 
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>, Rob Herring <robh@...nel.org>, 
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" <linux-rpi-kernel@...ts.infradead.org>, 
	"moderated list:BROADCOM BCM2711/BCM2835 ARM ARCHITECTURE" <linux-arm-kernel@...ts.infradead.org>, 
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1 2/6] PCI: brcmstb: Fix error path upon call of regulator_bulk_get()

On Thu, Feb 6, 2025 at 1:34 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
>
> On Thu, Feb 06, 2025 at 01:22:54PM -0500, Jim Quinlan wrote:
> > On Thu, Feb 6, 2025 at 12:29 PM Bjorn Helgaas <helgaas@...nel.org> wrote:
> > > On Wed, Feb 05, 2025 at 02:12:02PM -0500, Jim Quinlan wrote:
> > > > If regulator_bulk_get() returns an error, no regulators are
> > > > created and we need to set their number to zero.  If we do
> > > > not do this and the PCIe link-up fails, regulator_bulk_free()
> > > > will be invoked and effect a panic.
> > > >
> > > > Also print out the error value, as we cannot return an error
> > > > upwards as Linux will WARN on an error from add_bus().
>
> > > > Fixes: 9e6be018b263 ("PCI: brcmstb: Enable child bus device regulators from DT")
> > > > Signed-off-by: Jim Quinlan <james.quinlan@...adcom.com>
> > > > ---
> > > >  drivers/pci/controller/pcie-brcmstb.c | 3 ++-
> > > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/pci/controller/pcie-brcmstb.c b/drivers/pci/controller/pcie-brcmstb.c
> > > > index f8fc3d620ee2..bf919467cbcd 100644
> > > > --- a/drivers/pci/controller/pcie-brcmstb.c
> > > > +++ b/drivers/pci/controller/pcie-brcmstb.c
> > > > @@ -1417,7 +1417,8 @@ static int brcm_pcie_add_bus(struct pci_bus *bus)
> > > >
> > > >               ret = regulator_bulk_get(dev, sr->num_supplies, sr->supplies);
> > > >               if (ret) {
> > > > -                     dev_info(dev, "No regulators for downstream device\n");
> > > > +                     dev_info(dev, "Did not get regulators; err=%d\n", ret);
> > > > +                     sr->num_supplies = 0;
> > > >                       goto no_regulators;
> > >
> > > I think it might have been better if we could do the
> > > regulator_bulk_get() separately, before pci_host_probe(), so that if
> > > this error happens, we can deal with it more easily.
> >
> > Keep in mind that brcm_pcie_add_bus() cannot return a non-zero error
> > code, as it will get a WARN() from the caller if it does.
> >
> > Would you  accept deallocating the "sr" array and setting it to NULL
> > like the following error condition does?  In that way we would not be
> > invoking any regulator_bulk_xxxx() functions with nr==0.  I'm really
> > wary of moving things around...
>
> Yeah, don't move anything around right now.  My wondering is just
> about whether the alloc and bulk_get() could be done earlier, leaving
> only the bulk_enable() to be done in brcm_pcie_add_bus().
>
> The alloc and bulk_get() depend on DT things and it's nice to catch
> those errors earlier.

IIRC, I believe the reason that this code is in
brcm_pcie_{add,remove}_bus() is because the reviewers wanted the code
outside of the RC driver, as it was the port driver that "owned'  the
regulator.  I also vaguely recall one of my submissions that had
generic pci_subdev_regulators_{add,remove}_bus()  calls in pcie/bus.c,
but  was  later redirected back to the brcmstb RC driver.

Regards,
Jim Quinlan
Broadcom STB/CM
>
> Bjorn

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