Re: [PATCH v8 10/13] PCI/acpiphp: do not use ACPI PCI subdriver mechanism

[Yijing Wang <wangyijing@huawei.com>]

>> Hi Bjorn,
>>         Thanks for review.
>>
>>> My goal is that a user should never have to specify a kernel boot
>>> parameter or edit a modules.conf file, but the user did previously
>>> have some way to influence whether we use pciehp or acpiphp.  I know
>>> we still have some issues, particularly with acpiphp, so I'm a little
>>> concerned that by removing the CONFIG_HOTPLUG_PCI_ACPI=m, we might be
>>> removing a way to work around those issues.
>>>
>>> A distro that previously used CONFIG_HOTPLUG_PCI_ACPI=m will now have
>>> to use =y, so modules.conf is no longer applicable.  Can you convince
>>> me that the user still has a way to work around issues?  I spent quite
>>> a while trying to understand the pciehp/acpiphp dependencies, but it's
>>> pretty tangled web.
>> I will try my best to explain the relationships between pciehp and acpiphp
>> as of v3.9-rc6.
>>
>> The pciehp driver always have priority over the acpiphp driver.
>> That is, the acpiphp driver rejects binding to an ACPI PCI hotplug slot if
>> a) The slot's parent is a PCIe port with native hotplug capability
>> b) OSPM has taken over PCIe native hotplug control from BIOS.
>>         !(root->osc_control_set & OSC_PCI_EXPRESS_NATIVE_HP_CONTROL)
>> The above check has no dependency on the loading order of pciehp and acpiphp
>> drivers. So converting acpiphp driver to builit-in should be ok.
>>
>> On the other hand, I remember Yinghai has mentioned that some PCIe ports
>> with native hotplug capability doesn't work as expected with the pciehp driver
>> and should be managed by the acpiphp driver. Currently we could achieve that
>> by using boot param "pcie_ports=compat", but this will disable PCIe port
>> drivers altogether. And I also remember that Rafael has mentioned that
>> some BIOSes exhibit strange dependency among PCIe OSC controls, so it's
>> not feasible to only disable PCIe native hotplug.
>>
>> For "pciehp_force", it does only affect the way pciehp to detect a hotplug
>> slot, it doesn't affect acpiphp at all.
>>
>> To sum up, converting acpiphp as built-in should not affect the relationship
>> between pciehp and acpiphp driver.
> 
> My concern is that a user used to be able to remove acpiphp from
> modules.conf.  Now removing acpiphp will require a kernel rebuild.
> But maybe that won't turn out to be a problem.

Hi Bjorn,
   If user don't want to occupy the slot by acpiphp. Conservative approach, what about add a kernel parameter
to control acpiphp to enumerate slot ?

Thanks!
Yijing
> 
>> So how about splitting this patch into
>> two and adding more comments for the Kconfig change?
> 
> Yes, please at least split this into two.  While you're at it, please
> also split the first patch into "remove unnecessary is_added guard"
> and "cleanup."
> 
> Bjorn
> 
> .
> 


-- 
Thanks!
Yijing