Re: [PATCH] powerpc/rtas_pci: No hotplug on permanently removed device on pSeries

[Shivaprasad G Bhat <sbhat@linux.ibm.com>]

Hi Harsh,

On 5/12/26 11:14 PM, Harsh Prateek Bora wrote:
>
>
> On 12/05/26 10:47 pm, Harsh Prateek Bora wrote:
>>
>>
>> On 27/04/26 8:25 am, Shivaprasad G Bhat wrote:
>>> The eeh_driver disables and offlines the PE permanently when it
>>> exceeds the freeze count beyond eeh_max_freeze within the last hour.
>>> The PE is only offline, so the device tree entries, eeh device
>>> references are all intact till the real unplug of the device from
>>> the guest/host takes place.
>>>
>>> On pSeries, with a new hotplug of any PCI device, the drmgr initiates
>>> a system-wide PCI rescan, which finds devices offlined by the 
>>> eeh_driver
>>> and there will be attempts to bring them online. This leads to
>>> recurring EEHs either at the config read time itself or a bit
>>> later depending on the type of the problem.
>>>
>>> For PowerNV, the commit d2b0f6f77ee5 ("powerpc/eeh: No hotplug on
>>> permanently removed dev") introduced the EEH_DEV_REMOVED flag to
>>> prevent such inadvertent rescans on hierarchical toplogies relavent in
>>> Baremetal setups. For pSeries, such topologies don't really make sense
>>> as the devices are either part of the same PE OR exposed as independent
>>> devices on multiple virtual PHBs. However, the inadvertent rescans are
>>> still a possibility with either hotplug of a new device or otherwise
>>> with manual system-wide pci bus rescan attempts.
>>>
>>> So the patch checks for EEH_DEV_REMOVED before allowing config space
>>> access just like PowerNV, making the PCI core omit the PE, and thus
>
> Also, not sure if this commit description is correct as the patch only
> changes behaviour of RTAS config-space accesses and not making changes
> for omission semantics.

This is for the pci core rescan attempts to be skipped, when rescan is 
attempted

with write to rescan sysfs file.

  pci_bus_generic_read_dev_vendor_id+0x48/0x220
  pci_scan_single_device+0xa8/0x130
  pci_scan_slot+0x9c/0x2e0
  pci_scan_child_bus_extend+0x70/0x410
  pci_rescan_bus+0x2c/0x70
  rescan_store+0xa4/0xe0
  bus_attr_store+0x3c/0x60
  sysfs_kf_write+0xb0/0xe0

> The existing code in arch/powerpc/kernel/pci_of_scan.c already
> suppresses discovery of removed device:
>
> #ifdef CONFIG_EEH
>         if (edev && (edev->mode & EEH_DEV_REMOVED))
>                 return NULL;
> #endif
>
This is boot time only scan from the pcibios_init() path.


>>> preventing subsequent EEH recurances. The patch is tested on PowerVM
>>> and KVM machines with single and multi-function devices, and on the
>>> devices behind a switch. The unplug of the affected devices post EEH
>>> removal is also working fine as expected.
>>>
>>> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
>>> References: d2b0f6f77ee5 ("powerpc/eeh: No hotplug on permanently 
>>> removed dev")
>>> ---
>>>   arch/powerpc/kernel/rtas_pci.c |    6 ++++++
>>>   1 file changed, 6 insertions(+)
>>>
>>> diff --git a/arch/powerpc/kernel/rtas_pci.c b/arch/powerpc/kernel/ 
>>> rtas_pci.c
>>> index fccf96e897f6..ce24b18712ca 100644
>>> --- a/arch/powerpc/kernel/rtas_pci.c
>>> +++ b/arch/powerpc/kernel/rtas_pci.c
>>> @@ -57,6 +57,9 @@ int rtas_pci_dn_read_config(struct pci_dn *pdn, 
>>> int where, int size, u32 *val)
>>>       if (pdn->edev && pdn->edev->pe &&
>>>           (pdn->edev->pe->state & EEH_PE_CFG_BLOCKED))
>>>           return PCIBIOS_SET_FAILED;
>>> +
>>> +    if (pdn->edev && pdn->edev->mode & EEH_DEV_REMOVED)
>>
>> Consider using paranthesis for (pdn->edev->mode & EEH_DEV_REMOVED) 
>> and moving to next line for readability (similar to prev one).
Sure.
>>
>>> +        return PCIBIOS_SET_FAILED;
>>
>> Why not return PCIBIOS_DEVICE_NOT_FOUND ? Returning SET_FAILED for a 
>> removed device could be misleading.
>>
>

Sure.


> Also we should check for EEH_DEV_REMOVED before checking for
> EEH_PE_CFG_BLOCKED to avoid returning early when the latter is still set
> for a removed device.
>
Sure.


v2 posted here - 
https://lore.kernel.org/all/178246517230.1267.12206176311111155505.stgit@linux.ibm.com/


Thanks,

Shivaprasad

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