[PATCH 1/2] PCI: iproc: Support DT property for ignoring aborts when probing

[Ray Jui]

On 4/11/2016 3:26 PM, Scott Branden wrote:
> One Comment below
>
> On 16-04-11 03:24 PM, Ray Jui wrote:
>>
>>
>> On 4/11/2016 2:55 PM, Florian Fainelli wrote:
>>> On 11/04/16 13:06, Ray Jui wrote:
>>>>
>>>>
>>>> On 4/10/2016 6:43 PM, Florian Fainelli wrote:
>>>>> On April 9, 2016 2:50:23 PM PDT, "Rafał Miłecki" <zajec5 at gmail.com>
>>>>> wrote:
>>>>>> Some devices (e.g. Northstar ones) may have bridges that forward
>>>>>> harmless errors to the ARM core. In such case we need an option to
>>>>>> add a handler ignoring them.
>>>>>>
>>>>>> Signed-off-by: Rafał Miłecki <zajec5 at gmail.com>
>>>>>> ---
>>>>>
>>>>>> +- brcm,pcie-hook-abort-handler: During PCI bus probing (device
>>>>>> enumeration)
>>>>>> +  there can be errors that are expected and harmless. Unfortunately
>>>>>> some bridges
>>>>>> +  can't be configured to ignore them and they forward them to the
>>>>>> ARM
>>>>>> core
>>>>>> +  triggering die().
>>>>>> +  This property should be set in such case, it will make driver add
>>>>>> its own
>>>>>> +  handler ignoring such errors.
>>>>>
>>>>> The property is named after the function that allows you to catch
>>>>> abort handlers, whereas you should be describing the HW here.
>>>>> Something like brcm,bridge-error-forward or a better name even would
>>>>> be preferable.
>>>>>
>>>>>> +#ifdef CONFIG_ARM
>>>>>> +static int iproc_pcie_abort_handler(unsigned long addr, unsigned int
>>>>>> fsr,
>>>>>> +                    struct pt_regs *regs)
>>>>>> +{
>>>>>> +    if (fsr == 0x1406)
>>>>>> +        return 0;
>>>>>> +
>>>>>> +    return 1;
>>>>>
>>>>> As you later noted this prevents this driver from being a module now.
>>>>> Since the expectation is that either a fixed bootloader or a platform
>>>>> should enot produce these data aborts, or allow them to be ignored,
>>>>> why not just put this code back where it belongs in the machine
>>>>> specific file which kills many birds with the same stone:
>>>>>
>>>>
>>>> I assume the module compile issue can be simply fixed by exporting
>>>> symbol of "hook_fault_code"?
>>>
>>> I do not think it is desireable for this symbol to be exported in the
>>> first place, also last I looked, this was a one time registration thing,
>>> you cannot undo the hook you installed, but everything can be fixed.
>>>
>>
>> Okay.
>>
>>>>
>>>> I believe ARM64 based NS2 that uses the same iProc PCIe driver might
>>>> also need something like this (I'm still waiting for Jon Mason to give
>>>> me some more information on the NS2 errors that he saw, which is likely
>>>> related to this). I assume there will be something similar to the ARM
>>>> specific "hook_fault_code" for ARM64, but then ARM64 does not have any
>>>> "mach" specific directory. Where can this type of hook be installed for
>>>> ARM64 based platforms if not in the PCIe driver?
>>>
>>> OK, that is a fair point, then maybe have a two stage process, where we
>>> make sure that the part that installs the hook is always available and
>>> built-into the kernel, but let the iProc PCIe driver remain a module?
>>>
>>
>> I guess we are sort of stuck on this. If "hook_fault_code" is not
>> supposed to be used by any driver compiled as module like you described,
>> then yes, I agree, I don't see how we can leave this in the iProc PCIe
>> driver.
>>
> Why does thie PCI driver need to be compiled as module though?  Why
> can't we limit it to being linked in the kernel?
>
> Regards,
> Scott

There are minor benefits allowing this driver to be compiled as module, 
although in our use case (Cygnus and NS2), we always compile this driver 
as statically linked in the kernel. I'm not sure if NS/BCMA has any use 
case that requires this driver to be a module.

In fact, being able to compile this driver as a module and loaded after 
kernel init process is done just helped to confirm this imprecise abort 
issue to be PCIe specific, :)

Ray