linux-kernel - Re: [PATCH] drivers: pci: convert generic host controller to DT host bridge creation API

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Date:	Thu, 4 Sep 2014 17:02:17 +0100
From:	Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Will Deacon <Will.Deacon@....com>,
	Liviu Dudau <Liviu.Dudau@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Catalin Marinas <Catalin.Marinas@....com>,
	Jingoo Han <jg1.han@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Suravee Suthikulanit <suravee.suthikulpanit@....com>,
	linux-pci <linux-pci@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] drivers: pci: convert generic host controller to DT host
 bridge creation API

Hi Arnd,

thanks for having a look.

On Thu, Sep 04, 2014 at 03:05:53PM +0100, Arnd Bergmann wrote:
> On Thursday 04 September 2014 14:39:56 Lorenzo Pieralisi wrote:
> > > > +   if (!res_valid) {
> > > > +           dev_err(dev, "non-prefetchable memory resource required\n");
> > > > +           return -EINVAL;
> > > > +   }
> > > > +
> > > > +   if (iores) {
> > > > +           if (!PAGE_ALIGNED(io_cpuaddr))
> > > > +                   return -EINVAL;
> > > 
> > > Why is this alignment check not in the core code? Probably a question for
> > > somebody like Arnd, but do we need to deal with multiple IO resources?
> > > Currently we'll just silently take the last one that we found, which doesn't
> > > sound ideal.
> > 
> > (1) Yes, the alignment check should be made in core code
> 
> Makes sense. In theory we could support unaligned addresses (as long as
> the offset in the page is the same for virtual and physical), but I don't
> see why we should implement that unless some implementation absolutely
> requires it.
> 
> > (2) I could take the first IO resource and warn on multiple IO resources if
> >     they are detected. Thoughts ?
> 
> I think we should either warn, or be reasonably sure that it will work.
> Again, in theory this should work, but no sane hardware implementation
> would do it like that.

Ok, I will refactor the IO resources mapping code on top of Livius's v10.

> > > > +           if (err)
> > > > +                   return err;
> > > > +   }
> > > > +
> > > > +   /* Parse and map our Configuration Space windows */
> > > > +   err = gen_pci_parse_map_cfg_windows(host);
> > > > +   if (err)
> > > > +           return err;
> > > > +
> > > > +   pci_add_flags(PCI_ENABLE_PROC_DOMAINS);
> > > > +   pci_add_flags(PCI_REASSIGN_ALL_BUS | PCI_REASSIGN_ALL_RSRC);
> > > 
> > > Why does this belong in the host controller driver and how does it interact
> > > with the probe-only property?
> > 
> > That's a very good question and it is one that confuses me too.
> > 
> > Current code in pci_common_init_dev() sets PCI_REASSIGN_ALL_RSRC behind
> > our backs silently. That flag has a side effect only if the probing code
> > detects PCI bridges in the list of devices, since PCI core probing code
> > will try to reassign the bus numbers upon PCI bridge detection IIUC. I do
> > not think that PCI_REASSIGN_ALL_BUS has any side effect on ARM (by grepping
> > around I noticed that PCI_REASSIGN_ALL_RSRC is used in
> > 
> > pcibios_assign_all_busses()
> > 
> > which in turn is triggered only if PCI bridges are detected, still grokking
> > the code though).
> 
> Interesting point: the generic implementation should probably not default
> to reassigning all buses at all. We could have a (host controller specific,
> but with standardized name) DT property for it, but it would be best if
> firmware already probes it to not have to do it again.

I think that makes sense, let me point out though that this is
*not* how the code works today, since the pcibios code sets:

PCI_REASSIGN_ALL_RSRC (pci_common_init_dev() in arch/arm/kernel/bios32.c)

by default. I won't set the PCI_REASSIGN_ALL_RSRC and PCI_REASSIGN_ALL_BUS
flags.

> > Apart from the PCI_ENABLE_PROC_DOMAINS flag which I think it is safe to
> > set by default (but let me check that too),
> 
> I think it should be enabled here, as no legacy machine will use this
> driver.

+1

I will wait for Liviu's v10 and repost accordingly.

Lorenzo

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