linux-kernel - Re: [PATCH 1/1] pci: pciehp: Handle MRL interrupts to enable slot for hotplug.

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Date:   Sat, 21 Nov 2020 17:31:33 -0800
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Lukas Wunner <lukas@...ner.de>
Cc:     linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Sathyanarayanan Kuppuswamy <sathyanarayanan.kuppuswamy@...el.com>,
        linux-kernel@...r.kernel.org, Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH 1/1] pci: pciehp: Handle MRL interrupts to enable slot
 for hotplug.

On Sat, Nov 21, 2020 at 12:10:50PM +0100, Lukas Wunner wrote:
> 
> > > > +	/*
> > > > +	 * If ATTN is present and MRL is triggered
> > > > +	 * ignore the Presence Change Event.
> > > > +	 */
> > > > +	if (ATTN_BUTTN(ctrl) && (events & PCI_EXP_SLTSTA_MRLSC))
> > > > +		events &= ~PCI_EXP_SLTSTA_PDC;
> > > 
> > > An Attention Button press results in a synthesized PDC event after
> > > 5 seconds, which may get lost due to the above if-statement.
> > 
> > When its synthesized you don't get the MRLSC? So we won't nuke the PDC then
> > correct?
> 
> I just meant to say, pciehp_queue_pushbutton_work() will synthesize
> a PDC event after 5 seconds and with the above code snippet, if an
> MRL event happens simultaneously, that synthesized PDC event would
> be lost.  So I'd just drop the above code snippet.  I think you
> just need to subscribe to MRL events and propagate them to
> pciehp_handle_presence_or_link_change().  There, you'd bring down
> the slot if an MRL event has occurred (same as DLLSC or PDC).
> Then, check whether MRL is closed.  If so, and if presence or link
> is up, try to bring up the slot.
> 
> If the MRL is open when slot or presence has gone up, the slot is not
> brought up.  But once MRL is closed, there'll be another MRL event and
> *then* the slot is brought up.
> 

Sounds good.. I'll send the update patch.