linux-kernel - Re: [PATCH v3 05/10] s390/pci: Restore IRQ unconditionally for the zPCI device

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Message-ID: <d4ae1aede3a62ad60626e9706d11ed3c48f5a30a.camel@linux.ibm.com>
Date: Mon, 15 Sep 2025 10:39:03 +0200
From: Niklas Schnelle <schnelle@...ux.ibm.com>
To: Farhan Ali <alifm@...ux.ibm.com>, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org
Cc: alex.williamson@...hat.com, helgaas@...nel.org, mjrosato@...ux.ibm.com
Subject: Re: [PATCH v3 05/10] s390/pci: Restore IRQ unconditionally for the
 zPCI device

On Thu, 2025-09-11 at 11:33 -0700, Farhan Ali wrote:
> Commit c1e18c17bda6 ("s390/pci: add zpci_set_irq()/zpci_clear_irq()"),
> introduced the zpci_set_irq() and zpci_clear_irq(), to be used while
> resetting a zPCI device.
> 
> Commit da995d538d3a ("s390/pci: implement reset_slot for hotplug slot"),
> mentions zpci_clear_irq() being called in the path for zpci_hot_reset_device().
> But that is not the case anymore and these functions are not called
> outside of this file.

If you're doing another version I think you could add a bit more
information on why this still works for existing recovery based on my
investigation in
https://lore.kernel.org/lkml/052ebdbb6f2d38025ca4345ee51e4857e19bb0e4.camel@linux.ibm.com/

Even if you don't add more explanations, I'd tend to just drop the
above paragraph as it doesn't seem relevant and sounds like
zpci_hot_reset_device() doesn't clear IRQs. As explained in the linked
mail there really is no need to call zpci_clear_irq() in
zpci_hot_reset_device() as the CLP disable does disable IRQs. It's
really only the state tracking that can get screwed up but is also fine
for drivers which end up doing the tear down. 

> 
> However after a CLP disable/enable reset, the device's IRQ are
> unregistered, but the flag zdev->irq_registered does not get cleared. It
> creates an inconsistent state and so arch_restore_msi_irqs() doesn't
> correctly restore the device's IRQ. This becomes a problem when a PCI
> driver tries to restore the state of the device through
> pci_restore_state(). Restore IRQ unconditionally for the device and remove
> the irq_registered flag as its redundant.

s/its/it's/

> 
> Signed-off-by: Farhan Ali <alifm@...ux.ibm.com>
> ---
>  arch/s390/include/asm/pci.h | 1 -
>  arch/s390/pci/pci_irq.c     | 9 +--------
>  2 files changed, 1 insertion(+), 9 deletions(-)
> 
> diff --git a/arch/s390/include/asm/pci.h b/arch/s390/include/asm/pci.h
> index 41f900f693d9..aed19a1aa9d7 100644
> --- a/arch/s390/include/asm/pci.h
> +++ b/arch/s390/include/asm/pci.h
> @@ -145,7 +145,6 @@ struct zpci_dev {
>  	u8		has_resources	: 1;
>  	u8		is_physfn	: 1;
>  	u8		util_str_avail	: 1;
> -	u8		irqs_registered	: 1;
>  	u8		tid_avail	: 1;
>  	u8		rtr_avail	: 1; /* Relaxed translation allowed */
>  	unsigned int	devfn;		/* DEVFN part of the RID*/
> diff --git a/arch/s390/pci/pci_irq.c b/arch/s390/pci/pci_irq.c
> index 84482a921332..e73be96ce5fe 100644
> --- a/arch/s390/pci/pci_irq.c
> +++ b/arch/s390/pci/pci_irq.c
> @@ -107,9 +107,6 @@ static int zpci_set_irq(struct zpci_dev *zdev)
>  	else
>  		rc = zpci_set_airq(zdev);
>  
> -	if (!rc)
> -		zdev->irqs_registered = 1;
> -
>  	return rc;
>  }
>  
> @@ -123,9 +120,6 @@ static int zpci_clear_irq(struct zpci_dev *zdev)
>  	else
>  		rc = zpci_clear_airq(zdev);
>  
> -	if (!rc)
> -		zdev->irqs_registered = 0;
> -
>  	return rc;
>  }
>  
> @@ -427,8 +421,7 @@ bool arch_restore_msi_irqs(struct pci_dev *pdev)
>  {
>  	struct zpci_dev *zdev = to_zpci(pdev);
>  
> -	if (!zdev->irqs_registered)
> -		zpci_set_irq(zdev);
> +	zpci_set_irq(zdev);
>  	return true;
>  }
>  

Code looks good to me. With or without my suggestions for the commit
message:

Reviewed-by: Niklas Schnelle <schnelle@...ux.ibm.com>