linux-kernel - Re: [PATCH V6 08/13] PCI: generic, thunder: update to use generic ECAM API

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Date:	Sat, 16 Apr 2016 20:06:03 +0530
From:	Jayachandran C <jchandra@...adcom.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Tomasz Nowicki <tn@...ihalf.com>,
	Bjorn Helgaas <helgaas@...nel.org>,
	Will Deacon <will.deacon@....com>,
	Catalin Marinas <catalin.marinas@....com>, rafael@...nel.org,
	Hanjun Guo <hanjun.guo@...aro.org>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Sinan Kaya <okaya@...eaurora.org>, jiang.liu@...ux.intel.com,
	Jon Masters <jcm@...hat.com>, linaro-acpi@...ts.linaro.org,
	linux-pci@...r.kernel.org, Liviu.Dudau@....com,
	David Daney <ddaney@...iumnetworks.com>,
	linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
	robert.richter@...iumnetworks.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, Wangyijing <wangyijing@...wei.com>,
	Marcin Wojtas <mw@...ihalf.com>
Subject: Re: [PATCH V6 08/13] PCI: generic, thunder: update to use generic
 ECAM API

On Sat, Apr 16, 2016 at 1:01 PM, Arnd Bergmann <arnd@...db.de> wrote:
> On Saturday 16 April 2016 12:50:13 Jayachandran C wrote:
>> >
>> > I still think it would be better to keep the loadable PCI host drivers
>> > separate from the ACPI PCI infrastructure. There are a number of
>> > simplifications that we want to do to the DT based drivers in the long
>> > run, so it's better if that code is not shared at this level. Abstracting
>> > out the ECAM code is fine, but at that point you should be able to just
>> > call it from the ACPI layer.
>>
>> The issue is not with this patch (in my opinion). This patch is just
>> re-arranging how thunder specific data is maintained. Earlier it was
>> a container_of gen_pci, now it is ->priv of pci_config_window.
>>
>> I can see the issue in patches 12 and 13 of this patchset which adds
>> ACPI fixups into the thunder OF driver.
>
> Right, I commented on this one, because it seems to rearrange the code
> in order to do the later one.

Patches 11- 13 are not from me, and I am not completely on board
on the approach of adding the sections.We can look at reworking this.

>> The simple approach when doing modular PCI drivers would be to make
>> pci-thunder-*.c like pci-host-common.c, to be compiled in if configured.
>> The fie will contain all the Thunder quirks and can export
>> pci_thunder_ecam_ops.
>
> I would argue that we should not export anything from drivers/pci/host,
> those should really be standalone drivers that do not interact with other
> subsystems.

pci-host-common.c goes against being standalone. The files calling
pci_host_common_probe() are expected to have custom ECAM ops
the way it is written now. We need to have a reasonable way to share
those ECAM ops if needed by ACPI.

> How much code would you need to duplicate from thunder-ecam to have
> the same functionality available in ACPI? My expectation is that it's
> not really that much more compared to the code you need for sharing
> a single implementation, but you get a lower complexity here, which
> makes it easier to understand and to rework.

Like I wrote above, the sharing is really simple because both generic
ACPI and pci-host-common.c have been written for "ECAM with quirks".

The whole pci-thunder-*.c is to support thunder PCI quirks since the
generic OF is handled by pci-host-common.c and generic ECAM is now
separated -  duplicating the whole file for ACPI will be bad.

Any suggestions on how to do this better would be really welcome.

Thanks,
JC.