Re: [PATCH v2] PCI: Restore the original INTX_DISABLE bit by pcim_intx()

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Jan 27, 2025 at 05:00:25PM +0100, Takashi Iwai wrote:
> On Mon, 09 Dec 2024 14:15:19 +0100,
> Philipp Stanner wrote:
> > 
> > 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@vger.kernel.org # 6.11+
> > > > Link: https://lore.kernel.org/87v7xk2ps5.wl-tiwai@suse.de
> > > > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > > 
> > > Reviewed-by: Philipp Stanner <pstanner@redhat.com>
> > 
> > Hello,
> > 
> > it seems we forgot about this patch.
> > 
> > Regards,
> > P.
> 
> This has fallen through the cracks.
> Do I need to resubmit?

Oops, sorry, I did miss this.  I added to pci/for-linus for v6.14.  It
didn't apply quite cleanly, so take a look and make sure I resolved it
correctly:

https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/commit/?h=for-linus&id=d555ed45a5a10a813528c7685f432369d536ae3d

> > > 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;
> > > 
> >