Re: [PATCH 0/5] PCI: Add support to the Cadence PCIe controller

Cyrille Pitchen
2017-11-30T18:45:21Z

Hi all,

Le 30/11/2017 à 19:18, Lorenzo Pieralisi a écrit :
> On Thu, Nov 30, 2017 at 12:43:20PM +0530, Kishon Vijay Abraham I wrote:
>
> [...]
>
>>>> For linux-next, I applied this series on top of Kishon's patch
>>>> ("PCI: endpoint: Use EPC's device in dma_alloc_coherent/dma_free_coherent")
>>>> otherwise dma_alloc_coherent() fails when called by pci_epf_alloc_space().
>>>>
>>>> Also, I patched drivers/Makefile rather than drivers/pci/Makefile to make
>>>> the drivers/pci/cadence/pcie-cadence-ep.o linked after
>>
>> The reason to patch drivers/Makefile should be because pcie-cadence-ep has to
>> be compiled even when CONFIG_PCI is not enabled. CONFIG_PCI enables host
>> specific features and ENDPOINT shouldn't depend on CONFIG_PCI.
>>>> drivers/pci/endpoint/*.o objects, otherwise the built-in pci-cadence-ep
>>>> driver would be probed before the PCI endpoint framework would have been
>>>> initialized, which results in a kernel crash.
>>>
>>> Nice :( - isn't there a way to improve this (ie probe deferral or
>>> registering the EPF bus earlier) ?
>>>
>>>> I guess this is the reason why the "pci/dwc" line was also put in
>>>> drivers/Makefile, right after the "pci/endpoint" line.
>>>
>>> Or probably the other way around - see commit 5e8cb4033807
>>>
>>> @Kishon, thoughts ?
>>
>> Lorenzo, ordering Makefile is one way to initialize EP core before
>
> Makefile ordering is fragile, I do not like relying on it.
>
>> other drivers. the other way is to have PCI EP core have a different
>> initcall level.. subsys_initcall??
>
> Yes, registering the bus at eg postcore_initcall() as PCI does should do
> (if that's the problem this is solving) but still, the code must not
> crash if the ordering is not correct, we have to fix this regardless.
>
> I would appreciate if Cyrille can debug the cause of the kernel crash
> so that we can fix it in the longer term.
>

I had the crash kernel few weeks ago hence I have to test again to confirm
but if I remember correctly it was a NULL pointer dereferencing crash:

cdns_pcie_ep_probe()
|
+--> devm_pci_epc_create()
|
+--> __devm_pci_ep_create()
|
+--> __pci_epc_create()
|
+--> pci_ep_cfs_add_epc_group()
|
| /*
| * Here controllers_group is still NULL because
| * pci_ep_cfs_init() has not been called yet.
| */
+--> configfs_register_group(controllers_group, ...)
|
+--> link_group()
/* Dereferencing NULL pointer */

Best regards,

Cyrille

> Thanks,
> Lorenzo
>

--
Cyrille Pitchen, Free Electrons
Embedded Linux and Kernel engineering