Subject: LS1043A : "synchronous abort" at boot due to PCI config read

From: [email-masked] (Gilles Buloz)
Date: Wed, 2 May 2018 13:48:27 +0000

Le 02/05/2018 15:26, Bjorn Helgaas a ?crit :
> On Wed, May 02, 2018 at 12:57:31PM +0000, Gilles Buloz wrote:
>> 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.
>
>> --- 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.
>
>>   };
>>   
>>   /* 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.
>
>> +
>> +	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.
>
>> +	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?
>
>> +		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()).
>
>> +		}
>> +	} 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).
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.
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 "!"

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 ?