linux-kernel - Re: [PATCH V8 5/9] pci, acpi: add acpi hook to assign domain number.

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Message-ID: <20160610181836.GA7843@localhost>
Date:	Fri, 10 Jun 2016 13:18:36 -0500
From:	Bjorn Helgaas <helgaas@...nel.org>
To:	Tomasz Nowicki <tn@...ihalf.com>
Cc:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>, arnd@...db.de,
	will.deacon@....com, catalin.marinas@....com, rafael@...nel.org,
	hanjun.guo@...aro.org, okaya@...eaurora.org, jchandra@...adcom.com,
	robert.richter@...iumnetworks.com, mw@...ihalf.com,
	Liviu.Dudau@....com, ddaney@...iumnetworks.com,
	wangyijing@...wei.com, Suravee.Suthikulpanit@....com,
	msalter@...hat.com, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
	linux-kernel@...r.kernel.org, linaro-acpi@...ts.linaro.org,
	jcm@...hat.com, andrea.gallo@...aro.org, dhdang@....com,
	jeremy.linton@....com, liudongdong3@...wei.com, cov@...eaurora.org
Subject: Re: [PATCH V8 5/9] pci, acpi: add acpi hook to assign domain number.

On Fri, Jun 10, 2016 at 06:49:32PM +0200, Tomasz Nowicki wrote:
> On 10.06.2016 17:49, Lorenzo Pieralisi wrote:
> >On Fri, Jun 10, 2016 at 04:14:58PM +0100, Lorenzo Pieralisi wrote:
> >>Hi Bjorn, Tomasz,
> >>
> >>On Tue, Jun 07, 2016 at 07:15:59PM -0500, Bjorn Helgaas wrote:
> >>
> >>[...]
> >>
> >>>>diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> >>>>index eb431b5..2b52178 100644
> >>>>--- a/drivers/pci/pci.c
> >>>>+++ b/drivers/pci/pci.c
> >>>>@@ -7,6 +7,7 @@
> >>>>   *	Copyright 1997 -- 2000 Martin Mares <mj@....cz>
> >>>>   */
> >>>>
> >>>>+#include <linux/acpi.h>
> >>>>  #include <linux/kernel.h>
> >>>>  #include <linux/delay.h>
> >>>>  #include <linux/init.h>
> >>>>@@ -4941,7 +4942,7 @@ int pci_get_new_domain_nr(void)
> >>>>  }
> >>>>
> >>>>  #ifdef CONFIG_PCI_DOMAINS_GENERIC
> >>>>-void pci_bus_assign_domain_nr(struct pci_bus *bus, struct device *parent)
> >>>>+static int of_pci_bus_domain_nr(struct device *parent)
> >>>
> >>>Can we do a little cleanup before this patch?
> >>>
> >>>   - pci_bus_assign_domain_nr() is only used inside drivers/pci, so
> >>>     maybe we move the prototype to drivers/pci/pci.h?
> >>>
> >>>   - I don't really like the style of calling a function that
> >>>     internally assigns bus->domain_nr.  Could we do something like
> >>>     this instead?
> >>>
> >>>     int pci_bus_domain_nr(...)
> >>>     {
> >>>       ...
> >>>       return domain;
> >>>     }
> >>>
> >>>     ... pci_create_root_bus(...)
> >>>     {
> >>>       ...
> >>>       b->domain_nr = pci_bus_domain_nr(...);
> >>
> >>We noticed while preparing v9, that this would force us to
> >>write an empty pci_bus_domain_nr() prototype for
> >>!PCI_DOMAINS_GENERIC (ie every arch but ARM/ARM64) that should
> >>return 0 to keep current behaviour unchanged.
> >>
> >>That's why pci_bus_assign_domain_nr() was there, so that it
> >>was compiled out on !PCI_DOMAINS_GENERIC.
> >>
> >>I really would like v9 to be final so let's fix it before posting it
> >>shortly please.
> >>
> >>For the above we have three options:
> >>
> >>1) Leave code as-is in v8
> >>
> >>2) in pci_create_root_bus():
> >>#ifdef CONFIG_PCI_DOMAINS_GENERIC
> >>        b->domain_nr = pci_bus_domain_nr(...);
> >>#endif
> >>
> >>+ other changes requested above
> >>
> >>3) in pci_create_root_bus()
> >>
> >>b->domain_nr = pci_bus_domain_nr(...);
> >>
> >>unguarded and a stub:
> >>
> >>#ifndef CONFIG_PCI_DOMAINS_GENERIC
> >>static inline int pci_bus_domain_nr() { return 0; }
> >>#endif
> >>
> >>+ other changes requested above
> >
> >Actually, Tomasz made me notice that pci_bus.domain_nr is
> >only declared for CONFIG_PCI_DOMAINS_GENERIC so (3) is not
> >even an option and IMO (2) is not much nicer than code in
> >v8 as-is with an ifdef in the middle of pci_create_root_bus().
> >
> 
> To me (1) is nicer too. Bjorn what is your take on this? This is
> last bit before sending v9.

My preference is (2).  The ifdef in pci_create_root_bus() is a little
ugly, but I like it better because it will fit nicely into Arnd's
idea of having the native drivers allocate and fill in a host bridge
structure before calling the PCI core.  The domain is one thing those
drivers could fill in.  I like that model much better than having the
PCI core make callbacks to get information that we should have passed
in to begin with.

The current code suggests that assigning the domain is the PCI core's
responsibility, and that's not really the case -- for ACPI it's
totally up to pci_root.c, for other drivers it comes from the DT, and
for others it might depend on the driver's knowledge of the hardware
(I'm thinking of parisc, where, I think we currently put all the
bridges in the same domain, but IIRC they *could* each be in their own
domain with a full [bus 00-ff] range for each bridge because each
bridge has its own config space access mechanism).

But it's not that big a deal either way -- we could do this bit of
restructuring later, too.

Bjorn