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

David Daney
2015-12-22T18:29:31Z

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@cavium.com>
>>
>> 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@cavium.com>
>> ---
>> 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
>