linux-kernel - Re: [PATCH] Add option to passively listen for PCIE hotplug events

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Date:	Tue, 04 Nov 2008 14:46:20 +0900
From:	Kenji Kaneshige <kaneshige.kenji@...fujitsu.com>
To:	Matthew Garrett <mjg59@...f.ucam.org>
CC:	linux-pci@...r.kernel.org, kristen.c.accardi@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Add option to passively listen for PCIE hotplug events

Matthew Garrett wrote:
> On Tue, Nov 04, 2008 at 02:07:00AM +0000, Matthew Garrett wrote:
>> On Tue, Nov 04, 2008 at 10:58:11AM +0900, Kenji Kaneshige wrote:
>>>> 	t_slot->hpc_ops->get_adapter_status(t_slot, &value); /* Check if 
>>>> 	slot is occupied */
>>>> -	if (value && pciehp_force) {
>>>> +	if (value && (pciehp_force || pciehp_passive)) {
>>>> 		rc = pciehp_enable_slot(t_slot);
>>>> 		if (rc)	/* -ENODEV: shouldn't happen, but deal with it */
>>>> 			value = 0;
>> This code no longer runs in the pciehp_passive case. However, by the 
>> looks of it it still does in the resume case - that probably wants 
>> fixing.
> 
> Thinking about this - you said that the problem occurs because 
> pciehp_force=1 causes it to try to enable an already enabled slot, and 
> then tries to power down the slot as a result? It sounds like this code 
> should actually be checking whether the return value is ENODEV or 
> EINVAL, and in the latter case not powering the slot down. That sounds 
> like a separate bugfix that I'll send later on.
> 

I think the root cause of this problem is the following line.

>>>> 			value = 0;

I can't understand why the 'value' is set to 0 when pciehp_enable_slot()
returns error. The 'value' here is representing whether the slot is
occupied or not. Even if pciehp_enable_slot() returns error, it doesn't
mean slot is not occupied. So I think it is clearly wrong thing that
changing 'value' to 0 from 1 here.

How about just ignore the return value from pciehp_enable_slot()? The
code would be as follows.

	t_slot = pciehp_find_slot(ctrl, ctrl->slot_device_offset);
	t_slot->hpc_ops->get_adapter_status(t_slot, &value);
	if (value) {
		if (pciehp_force)
			pciehp_enable_slot(t_slot);
	} else {
		/* Power off the slot if not occupied, just in case */
		if (POWER_CTRL(ctrl))
			if (t_slot->hpc_ops->power_off_slot(t_slot))
				goto err_out_free_ctrl_slots;
	}

Thanks,
Kenji Kaneshige

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