linux-kernel - Re: [PATCH v2 6/9] PCI: cadence: Add host driver for Cadence PCIe controller

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Date:   Mon, 8 Jan 2018 16:44:20 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Cyrille Pitchen <cyrille.pitchen@...e-electrons.com>
Cc:     bhelgaas@...gle.com, kishon@...com, lorenzo.pieralisi@....com,
        linux-pci@...r.kernel.org, adouglas@...ence.com,
        stelford@...ence.com, dgary@...ence.com, kgopi@...ence.com,
        eandrews@...ence.com, thomas.petazzoni@...e-electrons.com,
        sureshp@...ence.com, nsekhar@...com, linux-kernel@...r.kernel.org,
        robh@...nel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 6/9] PCI: cadence: Add host driver for Cadence PCIe
 controller

On Fri, Dec 29, 2017 at 11:08:38PM +0100, Cyrille Pitchen wrote:
> Hi Bjorn,
> 
> Le 29/12/2017 à 00:01, Bjorn Helgaas a écrit :
> > On Mon, Dec 18, 2017 at 07:16:06PM +0100, Cyrille Pitchen wrote:
> >> This patch adds support to the Cadence PCIe controller in host mode.
> >>
> >> The "cadence/" entry in drivers/pci/Makefile is placed after the
> >> "endpoint/" entry so when the next patch introduces a EPC driver for the
> >> Cadence PCIe controller, drivers/pci/cadence/pcie-cadence-ep.o will be
> >> linked after drivers/pci/endpoint/*.o objects, otherwise the built-in
> >> pci-cadence-ep driver would be probed before the PCI endpoint libraries
> >> would have been initialized, which would result in a kernel crash.
> >>
> >> Signed-off-by: Cyrille Pitchen <cyrille.pitchen@...e-electrons.com>
> > 
> >> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> >> index 7284a7f6ad1e..a66ddb347798 100644
> >> --- a/drivers/pci/Makefile
> >> +++ b/drivers/pci/Makefile
> >> @@ -54,5 +54,6 @@ obj-y += host/
> >>  obj-y += switch/
> >>  
> >>  obj-$(CONFIG_PCI_ENDPOINT)	+= endpoint/
> >> +obj-$(CONFIG_PCI_CADENCE)	+= cadence/
> >>  # PCI dwc controller drivers
> >>  obj-y				+= dwc/
> > 
> > I don't like the fact that the cadence/ rule looks different than the
> > dwc/ rule for no obvious reason.  With some work, the dwc/ rule could
> > maybe be made to look like:
> 
> I've tried to understand why dwc uses obj-y instead of
> obj-$(CONFIG_PCIE_DW), here is what I've found:
> 
> In drivers/pci/dwc/Makefile there is some obj-$(CONFIG_ARM64) rule to
> generate the pcie-hisi.o object like there are other obj-$(CONFIG_ARM64)
> rules in drivers/pci/host/Makefile produce objects like pci-thunder-ecam.o
> for instance.

Right, I missed that pcie-hisi.o rule.  That one needs to be compiled
even if CONFIG_PCI_HISI is not enabled.

It might be useful to have a Makefile comment along the lines of:

  # pcie-hisi.o quirks are needed even without CONFIG_PCIE_DW

Bjorn