linux-kernel - Re: [PATCH v2] PCI: Restore the original INTX_DISABLE bit by pcim

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Message-ID: <5201b58b1b20f6af6104c4f9153545b7859bd22e.camel@redhat.com>
Date: Mon, 09 Dec 2024 14:15:19 +0100
From: Philipp Stanner <pstanner@...hat.com>
To: Takashi Iwai <tiwai@...e.de>, Bjorn Helgaas <bhelgaas@...gle.com>
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] PCI: Restore the original INTX_DISABLE bit by
 pcim_intx()

On Mon, 2024-11-04 at 10:14 +0100, Philipp Stanner wrote:
> On Thu, 2024-10-31 at 14:42 +0100, Takashi Iwai wrote:
> > pcim_intx() tries to restore the INTx bit at removal via devres,
> > but
> > there is a chance that it restores a wrong value.
> > Because the value to be restored is blindly assumed to be the
> > negative
> > of the enable argument, when a driver calls pcim_intx()
> > unnecessarily
> > for the already enabled state, it'll restore to the disabled state
> > in
> > turn.  That is, the function assumes the case like:
> > 
> >   // INTx == 1
> >   pcim_intx(pdev, 0); // old INTx value assumed to be 1 -> correct
> > 
> > but it might be like the following, too:
> > 
> >   // INTx == 0
> >   pcim_intx(pdev, 0); // old INTx value assumed to be 1 -> wrong
> > 
> > Also, when a driver calls pcim_intx() multiple times with different
> > enable argument values, the last one will win no matter what value
> > it
> > is.  This can lead to inconsistency, e.g.
> > 
> >   // INTx == 1
> >   pcim_intx(pdev, 0); // OK
> >   ...
> >   pcim_intx(pdev, 1); // now old INTx wrongly assumed to be 0
> > 
> > This patch addresses those inconsistencies by saving the original
> > INTx state at the first pcim_intx() call.  For that,
> > get_or_create_intx_devres() is folded into pcim_intx() caller side;
> > it allows us to simply check the already allocated devres and
> > record
> > the original INTx along with the devres_alloc() call.
> > 
> > Fixes: 25216afc9db5 ("PCI: Add managed pcim_intx()")
> > Cc: stable@...r.kernel.org # 6.11+
> > Link: https://lore.kernel.org/87v7xk2ps5.wl-tiwai@suse.de
> > Signed-off-by: Takashi Iwai <tiwai@...e.de>
> 
> Reviewed-by: Philipp Stanner <pstanner@...hat.com>

Hello,

it seems we forgot about this patch.

Regards,
P.


> 
> Nice!
> 
> > ---
> > v1->v2: refactoring, fold get_or_create_intx_devres() into the
> > caller
> > instead of retrieving the original INTx there.
> > Also add comments and improve the patch description.
> > 
> >  drivers/pci/devres.c | 34 +++++++++++++++++++---------------
> >  1 file changed, 19 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/pci/devres.c b/drivers/pci/devres.c
> > index b133967faef8..c93d4d4499a0 100644
> > --- a/drivers/pci/devres.c
> > +++ b/drivers/pci/devres.c
> > @@ -438,19 +438,12 @@ static void pcim_intx_restore(struct device
> > *dev, void *data)
> >  	__pcim_intx(pdev, res->orig_intx);
> >  }
> >  
> > -static struct pcim_intx_devres *get_or_create_intx_devres(struct
> > device *dev)
> > +static void save_orig_intx(struct pci_dev *pdev, struct
> > pcim_intx_devres *res)
> >  {
> > -	struct pcim_intx_devres *res;
> > +	u16 pci_command;
> >  
> > -	res = devres_find(dev, pcim_intx_restore, NULL, NULL);
> > -	if (res)
> > -		return res;
> > -
> > -	res = devres_alloc(pcim_intx_restore, sizeof(*res),
> > GFP_KERNEL);
> > -	if (res)
> > -		devres_add(dev, res);
> > -
> > -	return res;
> > +	pci_read_config_word(pdev, PCI_COMMAND, &pci_command);
> > +	res->orig_intx = !(pci_command &
> > PCI_COMMAND_INTX_DISABLE);
> >  }
> >  
> >  /**
> > @@ -466,12 +459,23 @@ static struct pcim_intx_devres
> > *get_or_create_intx_devres(struct device *dev)
> >  int pcim_intx(struct pci_dev *pdev, int enable)
> >  {
> >  	struct pcim_intx_devres *res;
> > +	struct device *dev = &pdev->dev;
> >  
> > -	res = get_or_create_intx_devres(&pdev->dev);
> > -	if (!res)
> > -		return -ENOMEM;
> > +	/*
> > +	 * pcim_intx() must only restore the INTx value that
> > existed
> > before the
> > +	 * driver was loaded, i.e., before it called pcim_intx()
> > for
> > the
> > +	 * first time.
> > +	 */
> > +	res = devres_find(dev, pcim_intx_restore, NULL, NULL);
> > +	if (!res) {
> > +		res = devres_alloc(pcim_intx_restore,
> > sizeof(*res),
> > GFP_KERNEL);
> > +		if (!res)
> > +			return -ENOMEM;
> > +
> > +		save_orig_intx(pdev, res);
> > +		devres_add(dev, res);
> > +	}
> >  
> > -	res->orig_intx = !enable;
> >  	__pcim_intx(pdev, enable);
> >  
> >  	return 0;
>