Re: [PATCH 1/2] PCI: generic: Refactor code to enable reuse by other drivers.

[David Daney]

On 12/22/2015 02:07 AM, Will Deacon wrote:
> On Mon, Dec 21, 2015 at 05:53:41PM -0800, David Daney wrote:
> > From: David Daney <david.daney@xxxxxxxxxx>
> >
> > No change in functionality.
> >
> > Move structure definitions into a separate header file.  Split probe
> > function in to two parts:
> >
> >     - a small driver specific probe function (gen_pci_probe)
> >
> >     - a common probe that can be used by other drivers
> >       (gen_pci_common_probe)
> >
> > Signed-off-by: David Daney <david.daney@xxxxxxxxxx>
> > ---
> >   drivers/pci/host/pci-host-generic.c | 53 ++++++++++++-----------------------
> >   drivers/pci/host/pci-host-generic.h | 56 +++++++++++++++++++++++++++++++++++++
> >   2 files changed, 74 insertions(+), 35 deletions(-)
> >   create mode 100644 drivers/pci/host/pci-host-generic.h
> >
> > diff --git a/drivers/pci/host/pci-host-generic.c b/drivers/pci/host/pci-host-generic.c
> > index 5434c90..e83cec7 100644
> > --- a/drivers/pci/host/pci-host-generic.c
> > +++ b/drivers/pci/host/pci-host-generic.c
[...]
> > -static int gen_pci_probe(struct platform_device *pdev)
> > +int gen_pci_common_probe(struct platform_device *pdev,
> > +			 struct gen_pci *pci)
>
> Whilst I'm fine with this patch, I don't know how Bjorn will feel about
> exposing this function outside of the generic host driver. We could avoid
> it by turning things upside-down and having the generic driver probe
> the other drivers by matching a compatible string with a probe function
> pointer, but I'd be interested to see what others think.

Note: I know that pci-host-generic is not built as a loadable module, but...

struct of_device_id, MODULE_DEVICE_TABLE, struct platform_driver and the 
registering of platform drivers is fairly well standardized in the 
kernel, and module loading userpace tools.

The struct of_device_id, MODULE_DEVICE_TABLE must really reside in the 
same module as the driver for the device.   We are creating a separate 
driver precisely because we don't want to mix all this ThunderX specific 
code into the pci-host-generic driver when it is used by arm-32bit and 
others.  This means that, at a minimum, we would have to export the 
pci-host-generic probe function so that it could be referenced by struct 
platform_driver in other modules.

This brings up the next problem.  How to attach driver specific data to 
the generic driver structures?  At first I tried augmenting  struct 
gen_pci_cfg_bus_ops with a callback .init() function to be called by the 
generic driver, but this would also require adding an an element to 
struct gen_pci to point to a driver specific data object.  It felt a 
little convoluted and complex.

This led me to the current design where struct gen_pci is embedded in 
the driver specific structure, and the allocation of this is done in the 
driver specific probe function.  No more callbacks, no additions to the 
pci-host-generic structures.  I think it is a little cleaner this way.

If there are suggestions as to how it can be made cleaner yet, I would 
be happy to implement and test them.

David Daney

> Will

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