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 09:31:59 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Jayachandran C <jchandra@...adcom.com>
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 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.

> 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.

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.

	Arnd