On Wed, May 02, 2018 at 01:48:27PM +0000, Gilles Buloz wrote:

Le 02/05/2018 15:26, Bjorn Helgaas a ?crit :

quoted

On Wed, May 02, 2018 at 12:57:31PM +0000, Gilles Buloz wrote:

quoted

Hi Bjorn,
See attached patch (tested ok this morning)

This looks good.  Minor comments below.

I can fix minor things myself, but I do need a signed-off-by from you
before applying (see
https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/process/submitting-patches.rst)

Please add a changelog, too, and include the patch inline (as opposed
to as an attachment) if possible.

quoted

--- include/linux/pci.h.orig	2018-03-26 16:51:18.050000000 +0000
+++ include/linux/pci.h	2018-04-30 18:29:14.140000000 +0000

@@ -193,6 +193,7 @@
  enum pci_bus_flags {
  	PCI_BUS_FLAGS_NO_MSI   = (__force pci_bus_flags_t) 1,
  	PCI_BUS_FLAGS_NO_MMRBC = (__force pci_bus_flags_t) 2,
+	PCI_BUS_FLAGS_NO_EXTCFG = (__force pci_bus_flags_t) 4,

Best if you can rebase this to v4.17-rc1.

quoted

  };
  
  /* These values come from the PCI Express Spec */

--- drivers/pci/probe.c.orig	2018-01-22 09:29:52.000000000 +0000
+++ drivers/pci/probe.c	2018-05-02 13:44:35.530000000 +0000

@@ -664,6 +664,23 @@
  	}
  }
  
+static bool pci_bridge_child_bus_ext_cfg_accessible(struct pci_dev *bridge)
+{
+	int pos;
+	u32 status;
+
+	if (!pci_is_pcie(bridge) || /* PCI/PCI bridge */
+	    (pci_pcie_type(bridge) == PCI_EXP_TYPE_PCIE_BRIDGE) || /* PCIe/PCI bridge in forward mode */
+	    (pci_pcie_type(bridge) == PCI_EXP_TYPE_PCI_BRIDGE)) {  /* PCIe/PCI bridge in reverse mode */
+		pos = pci_find_capability(bridge, PCI_CAP_ID_PCIX);
+		if (pos)
+			pci_read_config_dword(bridge, pos + PCI_X_STATUS, &status);
+		return pos && (status & (PCI_X_STATUS_266MHZ | PCI_X_STATUS_533MHZ));
+	}

Please arrange this so everything fits in 80 columns.

If you can split it into several simpler "if" statements rather
than one with a complicated expression, that would also be good.

quoted

+
+	return true;
+}
+
  static struct pci_bus *pci_alloc_child_bus(struct pci_bus *parent,
  					   struct pci_dev *bridge, int busnr)
  {

@@ -725,6 +742,19 @@
  	/* Create legacy_io and legacy_mem files for this bus */
  	pci_create_legacy_files(child);
  
+	/*
+	 * if bus_flags inherited from parent bus do not already report lack of extended config
+	 * space support, check if supported by child bus by checking its parent bridge
+	 */

Wrap to fit in 80 columns.

quoted

+	if (bridge && !(child->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG)) {

The double negative makes this a little bit hard to read.  Maybe it
could be improved by reversing the sense of something?

quoted

+		if (!pci_bridge_child_bus_ext_cfg_accessible(bridge)) {
+			child->bus_flags |= PCI_BUS_FLAGS_NO_EXTCFG;
+			dev_info(&child->dev, "extended config space not accessible due to parent bridge\n");

In v4.17-rc1, there's a pci_info() that should work here (instead of
dev_info()).

quoted

+		}
+	} else {
+		dev_info(&child->dev, "extended config space not accessible due to parent bus\n");
+	}
+
  	return child;
  }
  

@@ -1084,6 +1114,9 @@
  	u32 status;
  	u16 class;
  
+	if (dev->bus->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG)
+		return PCI_CFG_SPACE_SIZE;
+
  	class = dev->class >> 8;
  	if (class == PCI_CLASS_BRIDGE_HOST)
  		return pci_cfg_space_size_ext(dev);

.

OK I'm going to learn about signing (sorry this is my first
"official" patch).

Great, welcome!  The signoff is no big deal -- it's just plain text
(no crypto signature or anything) and it's basically just an assertion
that you wrote it and have the right to contribute it.

I'll download kernel v4.17-rc1 and write the patch for it; however I
hope I'll be able to test it on my platform without the freescale
addons I have on 4.1.35, because I don't want to send an untested
patch.

Don't worry too much about the 4.1 vs 4.17 issue.  If you tested it
on 4.1.35 that should be fine.

For "if (bridge && !(child->bus_flags & PCI_BUS_FLAGS_NO_EXTCFG))",
I don't understand what you mean with "double negative", as I only
have one "!"

The "!" and the "NO" part of "NO_EXTCFG" is what I meant.  E.g., maybe
the flag could be something like "COMPAT_CFG_ONLY" so there's no
negation in the test at all.

Do you think it's worth keeping the two dev_info() ? The code would
be smaller without; however this may help to have it for debug.
Maybe use _dbg instead of _info ?

Probably one pci_info() is enough as a clue that extended config space 
isn't available below this point in the hierarchy.

I personally don't like the _dbg() version because it's so complicated
to figure out when the output is enabled.

Bjorn