linux-kernel - Re: [PATCH RFC v2 2/4] PCI: pciehp: Do not turn off slot if presence comes up after link

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Message-ID: <20190221073634.snvazxlzgvjhilaz@wunner.de>
Date:   Thu, 21 Feb 2019 08:36:34 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     Alexandru Gagniuc <mr.nuke.me@...il.com>
Cc:     bhelgaas@...gle.com, austin_bolen@...l.com,
        alex_gagniuc@...lteam.com, keith.busch@...el.com,
        Shyam_Iyer@...l.com, okaya@...nel.org, linux-pci@...r.kernel.org,
        "Gustavo A. R. Silva" <gustavo@...eddedor.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC v2 2/4] PCI: pciehp: Do not turn off slot if presence
 comes up after link

On Tue, Feb 19, 2019 at 07:20:28PM -0600, Alexandru Gagniuc wrote:
> @@ -213,6 +213,21 @@ void pciehp_handle_disable_request(struct controller *ctrl)
>  	ctrl->request_result = pciehp_disable_slot(ctrl, SAFE_REMOVAL);
>  }
>  
> +static bool is_delayed_presence_up_event(struct controller *ctrl, u32 events)
> +{
> +	bool present, link_active;
> +
> +	if (!ctrl->inband_presence_disabled)
> +		return false;
> +
> +	present = pciehp_card_present(ctrl);
> +	link_active = pciehp_check_link_active(ctrl);
> +
> +	if (!present || !link_active || events & PCI_EXP_SLTSTA_DLLSC)
> +		return false;
> +
> +	return true;
> +}
>  void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)

Newline please after the closing curly brace.


> @@ -220,13 +235,22 @@ void pciehp_handle_presence_or_link_change(struct controller *ctrl, u32 events)
>  	/*
>  	 * If the slot is on and presence or link has changed, turn it off.
>  	 * Even if it's occupied again, we cannot assume the card is the same.
> +	 * When the card is swapped, we also expect a change in link state,
> +	 * without which, it's likely presence became high after link-active.
>  	 */

Maybe it's just me but I find the code comment difficult to understand.
How about something along the lines of:

 	/*
 	 * If the slot is on and presence or link has changed, turn it off.
 	 * Even if it's occupied again, we cannot assume the card is the same.
+	 *
+	 * An exception is a delayed "Card present" after a "Link Up".
+	 * This can happen on controllers with in-band presence disabled,
+	 * PCIe r5.0 sec X.Y.Z.
 	 */


>  	mutex_lock(&ctrl->state_lock);
> +	present = pciehp_card_present(ctrl);
> +	link_active = pciehp_check_link_active(ctrl);
>  	switch (ctrl->state) {

These two assignments appear to be superfluous as you're also performing
them in pciehp_check_link_active().

Thanks,

Lukas