linux-kernel - Re: [PATCH v2 1/2] PCI: dwc: Perform host

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Date:   Tue, 24 Aug 2021 13:15:49 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Krzysztof Wilczy??ski <kw@...ux.com>,
        Stanimir Varbanov <svarbanov@...sol.com>,
        linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] PCI: dwc: Perform host_init() before registering
 msi

On Tue 24 Aug 12:05 PDT 2021, Bjorn Helgaas wrote:

> On Mon, Aug 23, 2021 at 08:49:57AM -0700, Bjorn Andersson wrote:
> > On the Qualcomm sc8180x platform the bootloader does something related
> > to PCI that leaves a pending "msi" interrupt, which with the current
> > ordering often fires before init has a chance to enable the clocks that
> > are necessary for the interrupt handler to access the hardware.
> > 
> > Move the host_init() call before the registration of the "msi" interrupt
> > handler to ensure the host driver has a chance to enable the clocks.
> 
> Did you audit other drivers for similar issues?  If they do, we should
> fix them all at once.
> 

I only looked at the DesignWware drivers, in an attempt to find any
issues the proposed reordering.

The set of bugs causes by drivers registering interrupts before critical
resources tends to be rather visible and I don't know if there's much
value in speculatively "fixing" drivers.

E.g. a quick look through the drivers I see a similar pattern in
pci-tegra.c, but it's unlikely that they have the similar problem in
practice and I have no way to validate that a change to the order would
have a positive effect - or any side effects.


Or am I misunderstanding your request?

Regards,
Bjorn

> > The assignment of the bridge's ops and child_ops is moved along, because
> > at least the TI Keystone driver overwrites these in its host_init
> > callback.
> > 
> > Signed-off-by: Bjorn Andersson <bjorn.andersson@...aro.org>
> > ---
> > 
> > Changes since v1:
> > - New patch, instead of enabling resources in the qcom driver before jumping to
> >   dw_pcie_host_init(), per Rob Herring's suggestion.
> > 
> >  .../pci/controller/dwc/pcie-designware-host.c | 19 ++++++++++---------
> >  1 file changed, 10 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > index d1d9b8344ec9..f4755f3a03be 100644
> > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > @@ -335,6 +335,16 @@ int dw_pcie_host_init(struct pcie_port *pp)
> >  	if (pci->link_gen < 1)
> >  		pci->link_gen = of_pci_get_max_link_speed(np);
> >  
> > +	/* Set default bus ops */
> > +	bridge->ops = &dw_pcie_ops;
> > +	bridge->child_ops = &dw_child_pcie_ops;
> > +
> > +	if (pp->ops->host_init) {
> > +		ret = pp->ops->host_init(pp);
> > +		if (ret)
> > +			return ret;
> > +	}
> > +
> >  	if (pci_msi_enabled()) {
> >  		pp->has_msi_ctrl = !(pp->ops->msi_host_init ||
> >  				     of_property_read_bool(np, "msi-parent") ||
> > @@ -388,15 +398,6 @@ int dw_pcie_host_init(struct pcie_port *pp)
> >  		}
> >  	}
> >  
> > -	/* Set default bus ops */
> > -	bridge->ops = &dw_pcie_ops;
> > -	bridge->child_ops = &dw_child_pcie_ops;
> > -
> > -	if (pp->ops->host_init) {
> > -		ret = pp->ops->host_init(pp);
> > -		if (ret)
> > -			goto err_free_msi;
> > -	}
> >  	dw_pcie_iatu_detect(pci);
> >  
> >  	dw_pcie_setup_rc(pp);
> > -- 
> > 2.29.2
> >