Re: [PATCH v4 1/5] PCI: Add pci_bus_fixup_irqs().

[Matthew Minter <matt@masarand.com>]

On Wednesday 07 October 2015 18:08:47 Bjorn Helgaas wrote:
> [+cc Matthew]
> 
> On Wed, Oct 07, 2015 at 01:08:40PM -0700, David Daney wrote:
> > On 10/07/2015 12:44 PM, Bjorn Helgaas wrote:
> > >Hi David,
> > >
> > >On Fri, Oct 02, 2015 at 11:43:59AM -0700, David Daney wrote:
> > >>From: David Daney <david.daney@cavium.com>
> > >>
> > >>pci_bus_fixup_irqs() works like pci_fixup_irqs(), except it only does
> > >>the fixups for devices on the specified bus.
> > >>
> > >>Follow-on patch will use the new function.
> > >>
> > >>Signed-off-by: David Daney <david.daney@cavium.com>
> > >>---
> > >>No change from v2.
> > >>
> > >>  drivers/pci/setup-irq.c | 30 ++++++++++++++++++++++++++++++
> > >>  include/linux/pci.h     |  4 ++++
> > >>  2 files changed, 34 insertions(+)
> > >>
> > >>diff --git a/drivers/pci/setup-irq.c b/drivers/pci/setup-irq.c
> > >>index 95c225b..189ad17 100644
> > >>--- a/drivers/pci/setup-irq.c
> > >>+++ b/drivers/pci/setup-irq.c
> > >>@@ -66,3 +66,33 @@ void pci_fixup_irqs(u8 (*swizzle)(struct pci_dev *,
> > >>u8 *),> >>
> > >>  		pdev_fixup_irq(dev, swizzle, map_irq);
> > >>  
> > >>  }
> > >>  EXPORT_SYMBOL_GPL(pci_fixup_irqs);
> > >>
> > >>+
> > >>+struct pci_bus_fixup_cb_info {
> > >>+	u8 (*swizzle)(struct pci_dev *, u8 *);
> > >>+	int (*map_irq)(const struct pci_dev *, u8, u8);
> > >>+};
> > >>+
> > >>+static int pci_bus_fixup_irq_cb(struct pci_dev *dev, void *arg)
> > >>+{
> > >>+	struct pci_bus_fixup_cb_info *info = arg;
> > >>+
> > >>+	pdev_fixup_irq(dev, info->swizzle, info->map_irq);
> > >>+	return 0;
> > >>+}
> > >>+
> > >>+/*
> > >>+ * Fixup the irqs only for devices on the given bus using supplied
> > >>+ * swizzle and map_irq function pointers
> > >>+ */
> > >>+void pci_bus_fixup_irqs(struct pci_bus *bus,
> > >>+			u8 (*swizzle)(struct pci_dev *, u8 *),
> > >>+			int (*map_irq)(const struct pci_dev *, u8, u8))
> > >>+{
> > >>+	struct pci_bus_fixup_cb_info info;
> > >>+
> > >>+	info.swizzle = swizzle;
> > >>+	info.map_irq = map_irq;
> > >>+	pci_walk_bus(bus, pci_bus_fixup_irq_cb, &info);
> > >
> > >I don't like the existing pci_fixup_irqs(), so by transitivity, I
> > >don't like pci_bus_fixup_irqs() either.
> > 
> > We are in agreement with respect to this point.
> > 
> > > The problem is that in both
> > >
> > >cases this is a one-time pass over the tree, so we don't handle
> > >hot-added devices correctly.
> > >
> > >I think we need to get rid of pci_fixup_irqs() and somehow integrate
> > >it into the pci_device_add() path, where it would be done once for
> > >every device we enumerate.
> > 
> > I also agree with this point.
> > 
> > > If we did that, I don't think you would
> > >
> > >need to add pci_bus_fixup_irqs(), would you?
> > 
> > Nope.
> > 
> > However, such a change is essentially untestable by me.  So, I
> > didn't attempt it.   pci_fixup_irqs() is used by alpha, arm, m68k,
> > mips, sh, sparc, tile, unicore32 and other things as well.  If the
> > core pci_device_add() code were to suddenly start doing the fixup,
> > there would be the potential to break all these things I cannot
> > test.
> 
> Yep, that's certainly a risk.  I can't test all those arches either,
> but I think it's a risk worth taking because the end result is more
> maintainable.
> 
> Matthew Minter did some really nice work on this last year, but it got
> stalled somehow.  I wonder if we can resurrect it?  It seems like it
> was pretty close to being ready.  Here's a pointer to the last posting
> I saw:
> 
> http://lkml.kernel.org/r/1412222866-21068-1-git-send-email-matt@masarand.com
> 
> Bjorn

Thanks for adding me into the loop,

Yes, I had been working on this last year, and got a patchset that was tested 
on arm, x86 (and amd64), and slightly tested on powerpc. However I was not 
able to test other architectures as they were not available in the software 
lab I work in but should in theory work on all arches the kernel runs on.

I can say that that patchset is being used by several projects out of tree 
currently but unfortunately due to a shift in priorities in the lab I was 
working for I lost access to the resources to develop and test the patch 
easily.

I have done some additional work personally on it but so far have not got 
anything that I am happy to submit for inclusion in tree. (due to a number of 
issues in structure and  a complication relating to weak functions where 
multiple variations of the same arch exist.

You can see in thread that is linked above 
(http://lkml.kernel.org/r/1412222866-21068-1-git-send-email-matt@masarand.com)
some feedback on the issues that need to be solved.

I also expect that the patchset needs to be pulled forward to a newer kernel 
as I have been working in a frozen tree without rebasing to reduce test 
complexity.

I would be happy to put some time this weekend if possible into reviewing the 
state of this and seeing if I can at least put together a version running on a 
recent kernel. I can also go over the issues again which were proving 
problematic and see if any of them are easy to fix.

However I can only work on this in my own time for now and on my own boxes 
(which are all x86 and amd64) so the amount I can do will be limited. However 
any assistance in fixing the issues would be appreciated, I will try and throw 
up a git repo somewhere this weekend with the latest patches if anyone is able 
to take a look.

In the mean time, the biggest issues with the current iteration and the full 
thread are here:

http://comments.gmane.org/gmane.linux.kernel.pci/35756

I will get a repo somewhere online for browsing soon but cannot quite yet as I 
need to clean up the repo a little first.

Kind regards to all,
Matthew Minter