linux-kernel - Re: [PATCH] misc/GenWQE: fix pci_enable

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Date:	Fri, 18 Jul 2014 10:46:20 +0200 (CEST)
From:	Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:	Frank Haverkamp <haver@...ux.vnet.ibm.com>
cc:	Bjorn Helgaas <bhelgaas@...gle.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Alexander Gordeev <agordeev@...hat.com>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] misc/GenWQE: fix pci_enable_msi usage

On Thu, 17 Jul 2014, Frank Haverkamp wrote:
> Hi Bjorn and Sebastian,
> 
> Am Mittwoch, den 16.07.2014, 15:10 -0600 schrieb Bjorn Helgaas:
> > [+cc linux-pci]
> > 
> > On Wed, Jul 09, 2014 at 12:46:39PM +0200, Sebastian Ott wrote:
> > > GenWQE used to call pci_enable_msi_block to allocate a desired number
> > > of MSI's. If that was not possible pci_enable_msi_block returned with a
> > > smaller number which might be possible to allocate. GenWQE then called
> > > pci_enable_msi_block with that number.
> > > 
> > > Since commit a30d0108b
> > > "GenWQE: Use pci_enable_msi_exact() instead of pci_enable_msi_block()"
> > > pci_enable_msi_exact is used which fails if the desired number of MSI's
> > > was not possible to allocate. Change GenWQE to use pci_enable_msi_range
> > > to restore the old behavior.
> > > 
> > > Signed-off-by: Sebastian Ott <sebott@...ux.vnet.ibm.com>
> > 
> > Since this fixes a30d0108b09a, which we merged via my tree in v3.16-rc1, I
> > applied this with Alexander and Frank's acks to for-linus for v3.16,
> > thanks!
> > 
> > > ---
> > >  drivers/misc/genwqe/card_ddcb.c  |  4 +---
> > >  drivers/misc/genwqe/card_utils.c | 10 ++++++----
> > >  2 files changed, 7 insertions(+), 7 deletions(-)
> > > 
> > > diff --git a/drivers/misc/genwqe/card_ddcb.c b/drivers/misc/genwqe/card_ddcb.c
> > > index c8046db..f66d43d 100644
> > > --- a/drivers/misc/genwqe/card_ddcb.c
> > > +++ b/drivers/misc/genwqe/card_ddcb.c
> > > @@ -1237,9 +1237,7 @@ int genwqe_setup_service_layer(struct genwqe_dev *cd)
> > >  	}
> > >  
> > >  	rc = genwqe_set_interrupt_capability(cd, GENWQE_MSI_IRQS);
> > > -	if (rc > 0)
> > > -		rc = genwqe_set_interrupt_capability(cd, rc);
> > > -	if (rc != 0) {
> > > +	if (rc) {
> > >  		rc = -ENODEV;
> > >  		goto stop_kthread;
> > >  	}
> > > diff --git a/drivers/misc/genwqe/card_utils.c b/drivers/misc/genwqe/card_utils.c
> > > index 62cc6bb..6abc437 100644
> > > --- a/drivers/misc/genwqe/card_utils.c
> > > +++ b/drivers/misc/genwqe/card_utils.c
> > > @@ -718,10 +718,12 @@ int genwqe_set_interrupt_capability(struct genwqe_dev *cd, int count)
> > >  	int rc;
> > >  	struct pci_dev *pci_dev = cd->pci_dev;
> > >  
> > > -	rc = pci_enable_msi_exact(pci_dev, count);
> > > -	if (rc == 0)
> > > -		cd->flags |= GENWQE_FLAG_MSI_ENABLED;
> > > -	return rc;
> > > +	rc = pci_enable_msi_range(pci_dev, 1, count);
> > > +	if (rc < 0)
> > > +		return rc;
> > > +
> > > +	cd->flags |= GENWQE_FLAG_MSI_ENABLED;
> > > +	return 0;
> > >  }
> 
> The original code tried to register for 4 interrupts. On my system the
> following scenario was executed:
> 
> We tried to register for 4 MSI interrupts, which was the original plan
> of interrupts for the card. Linux returned that it could not do that and
> that just 1 would work. We tried to register for 1 MSI interrupt and it
> worked. GENWQE_MSI_IRQS is still 4. That is how my original version
> looked like:

I changed the code that way, because I was under the impression
GENWQE_MSI_IRQS was set to 4 for a reason (I have no knowledge of the
internal workings of this driver). A lot of archs don't support more than
one MSI anyway - but are you saying that the genwqe card/driver itself
doesn't support more than one MSI?

Regards,
Sebastian
> 
>         rc = genwqe_set_interrupt_capability(cd, GENWQE_MSI_IRQS);
>         if (rc > 0)
>                 rc = genwqe_set_interrupt_capability(cd, rc);
>         if (rc != 0) {
>                 rc = -ENODEV;
>                 goto stop_kthread;
>         }
> 
> So genwqe_set_interrupt_capability() was indeed called two times.
> Calling it with 4 returned with rc=1 and no interrupts enabled. So
> calling it a 2nd time with rc=1 was leading to the proper enablement.
> 
> I think the simplest way is to set GENWQE_MSI_IRQS to 1. The rest of the
> code at least assumes just one interrupt, because 4 never worked.
> 
> Regards
> 
> Frank
> 
> 

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