linux-kernel - Re: [PATCH] PCI: pciehp: Use appropriate conditions to check the hotplug controller status

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Date: Mon, 27 May 2024 17:43:29 +0800
From: yaoma <yaoma@...ux.alibaba.com>
To: Lukas Wunner <lukas@...ner.de>
Cc: yaoma <yaoma@...ux.alibaba.com>,
 bhelgaas@...gle.com,
 weirongguang@...inos.cn,
 kanie@...ux.alibaba.com,
 linux-pci@...r.kernel.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI: pciehp: Use appropriate conditions to check the
 hotplug controller status

Hi,

> 2024年5月27日 16:50，Lukas Wunner <lukas@...ner.de> 写道：
> 
> On Sun, May 26, 2024 at 10:45:36PM +0800, yaoma wrote:
>>> 2024 5 24 15:53 Lukas Wunner <lukas@...ner.de>
>>> On Fri, May 24, 2024 at 02:30:23PM +0800, Bitao Hu wrote:
>>>> The values of 'present' and 'link_active' have similar meanings:
>>>> the value is %1 if the status is ready, and %0 if it is not. If the
>>>> hotplug controller itself is not available, the value should be
>>>> %-ENODEV. However, both %1 and %-ENODEV are considered true, which
>>>> obviously does not meet expectations. 'Slot(xx): Card present' and
>>>> 'Slot(xx): Link Up' should only be output when the value is %1.
>>> [...]
>>>> --- a/drivers/pci/hotplug/pciehp_ctrl.c
>>>> +++ b/drivers/pci/hotplug/pciehp_ctrl.c
>>>> @@ -276,10 +276,10 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>>>> 	case OFF_STATE:
>>>> 		ctrl->state = POWERON_STATE;
>>>> 		mutex_unlock(&ctrl->state_lock);
>>>> -		if (present)
>>>> +		if (present > 0)
>>>> 			ctrl_info(ctrl, "Slot(%s): Card present\n",
>>>> 				  slot_name(ctrl));
>>>> -		if (link_active)
>>>> +		if (link_active > 0)
>>>> 			ctrl_info(ctrl, "Slot(%s): Link Up\n",
>>>> 				  slot_name(ctrl));
>>>> 		ctrl->request_result = pciehp_enable_slot(ctrl);
>>> 
>>> We already handle the "<= 0" case immediately above this code excerpt:
>>> 
>>> 	if (present <= 0 && link_active <= 0) {
>>> 	...
>>> 	}
>> 
>> I'm not sure if the following scenarios would occur in actual production
>> environment, but from the code level, there is the possibility of
>> "present <= 0 && link_active > 0" or "present > 0 && link_active <= 0".
>> In these cases, the "<= 0" conditions will not be properly handled,
>> and "ctrl_info" will output incorrect prompt messages.
> 
> I see, that makes sense.
> 
> "present" and "link_active" can be -ENODEV if reading the config space
> of the hotplug port failed.  That's typically the case if the hotplug
> port itself was hot-removed, which happens all the time with
> Thunderbolt/USB4.
> 
> E.g. pciehp_card_present() may return 1 and pciehp_check_link_active()
> may return -ENODEV because the hotplug port was hot-removed in-between
> the two function calls.  In that case we'll emit both "Card present"
> *and* "Link Up".  The latter is uncalled for and is supressed by your
> patch.
> 
> So your code change is
> Reviewed-by: Lukas Wunner <lukas@...ner.de>
> 
> ...but it would be good if you could respin the patch and explain the
> rationale of the code change in the commit message more clearly.
> Basically summarize what you and I have explained above.
> 
> Also, the percent sign % in front of 0, 1, -ENODEV is unnecessary in
> commit messages. It only has special meaning in kernel-doc.
> 

Thanks for your analysis. I will make the the rationale of the code change
more clearly in next patch.

Best Regards,

	Bitao Hu