linux-kernel - Re: [PATCH] PCI/LINK: bw_notification: Do not leave interrupt handler NULL

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Date:   Tue, 19 Mar 2019 20:25:50 +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,
        torvalds@...ux-foundation.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PCI/LINK: bw_notification: Do not leave interrupt
 handler NULL

On Mon, Mar 18, 2019 at 08:12:04PM -0500, Alexandru Gagniuc wrote:
> A threaded IRQ with a NULL handler does not work with level-triggered
> interrupts. request_threaded_irq() will return an error:
> 
>   genirq: Threaded irq requested with handler=NULL and !ONESHOT for irq 16
>   pcie_bw_notification: probe of 0000:00:1b.0:pcie010 failed with error -22
> 
> For level interrupts we need to silence the interrupt before exiting
> the IRQ handler, so just clear the PCI_EXP_LNKSTA_LBMS bit there.
> 
> Reported-by: Linus Torvalds <torvalds@...ux-foundation.org>
> Signed-off-by: Alexandru Gagniuc <mr.nuke.me@...il.com>

I've tested this on my Ivy Bridge MacBook Pro which uses INTx on root and
downstream ports and I'm not seeing probe errors, so:

Tested-by: Lukas Wunner <lukas@...ner.de>


> @@ -67,8 +77,8 @@ static irqreturn_t pcie_bw_notification_handler(int irq, void *context)
>  		__pcie_print_link_status(dev, false);
>  	up_read(&pci_bus_sem);
>  
> +	pcie_capability_read_word(port, PCI_EXP_LNKSTA, &link_status);
>  	pcie_update_link_speed(port->subordinate, link_status);
> -	pcie_capability_write_word(port, PCI_EXP_LNKSTA, events);
>  	return IRQ_HANDLED;
>  }

I'd suggest leaving the call to pcie_update_link_speed() in
pcie_bw_notification_irq() to avoid the duplicate read of the
Link Status register.

With that addressed,
Reviewed-by: Lukas Wunner <lukas@...ner.de>

Thanks,

Lukas