linux-kernel - Re: [Patch v2 1/1] PCI: pciehp: Add support for handling MRL events

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Message-ID: <20201210205719.GA25769@wunner.de>
Date:   Thu, 10 Dec 2020 21:57:19 +0100
From:   Lukas Wunner <lukas@...ner.de>
To:     "Raj, Ashok" <ashok.raj@...el.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org,
        Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...el.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [Patch v2 1/1] PCI: pciehp: Add support for handling MRL events

On Thu, Dec 03, 2020 at 02:51:24PM -0800, Raj, Ashok wrote:
> - Press ATTN, 
> - Slot is empty
> - After 5 seconds synthetic PDC arrives.
>   but since no presence and no link active, we leave slot in 
>   BLINKINGON_STATE, and led keeps blinking
> 
> if someone were to add a card after the 5 seconds, no hot-add is processed
> since we don't get notifications for PDC events when ATTN exists.
> 
> Can we automatically cancel the blinking and return slot back to OFF_STATE?

Yes.


> If the operation initiated by the attention button fails for any reason, it
> is recommended that system software present an error message explaining
> failure via a software user interface, or add the error message to system
> log.

Ah so we're supposed to log a message if the slot is empty.
That needs to be added then to the code snippet I sent you
yesterday in response to your off-list e-mail.


> Alternately we can also choose to subscribe to PDC, but ignore if slot is
> in OFF_STATE. So we let ATTN drive the add. But if PDC happens and we are
> in BLINKINGON_STATE, then we can process the hot-add? Spec says a software
> recommendation, but i think the cancel after 5 seconds seems better?

That approach seems more complicated.  It's better to stop blinking
and return to OFF_STATE if after the 5 second interval the slot is
found to be empty.

Thanks,

Lukas