Message-ID: <ae081c36c49733b007a8946dceeec0af94fc449a.camel@redhat.com>
Date: Fri, 25 Oct 2024 10:37:57 +0200
From: Philipp Stanner <pstanner@...hat.com>
To: Takashi Iwai <tiwai@...e.de>
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Subject: Re: [PATCH 02/13] ALSA: hda_intel: Use always-managed version of
 pcim_intx()

On Thu, 2024-10-24 at 17:43 +0200, Takashi Iwai wrote:
> On Thu, 24 Oct 2024 10:02:59 +0200,
> Philipp Stanner wrote:
> > 
> > On Wed, 2024-10-23 at 17:03 +0200, Takashi Iwai wrote:
> > > On Wed, 23 Oct 2024 15:50:09 +0200,
> > > Philipp Stanner wrote:
> > > > 
> > > > On Tue, 2024-10-22 at 16:08 +0200, Takashi Iwai wrote:
> > > > > On Tue, 15 Oct 2024 20:51:12 +0200,
> > > > > Philipp Stanner wrote:
> > > > > > 
> > > > > > pci_intx() is a hybrid function which can sometimes be
> > > > > > managed
> > > > > > through
> > > > > > devres. To remove this hybrid nature from pci_intx(), it is
> > > > > > necessary to
> > > > > > port users to either an always-managed or a never-managed
> > > > > > version.
> > > > > > 
> > > > > > hda_intel enables its PCI-Device with pcim_enable_device().
> > > > > > Thus,
> > > > > > it needs
> > > > > > the always-managed version.
> > > > > > 
> > > > > > Replace pci_intx() with pcim_intx().
> > > > > > 
> > > > > > Signed-off-by: Philipp Stanner <pstanner@...hat.com>
> > > > > > ---
> > > > > >  sound/pci/hda/hda_intel.c | 2 +-
> > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/sound/pci/hda/hda_intel.c
> > > > > > b/sound/pci/hda/hda_intel.c
> > > > > > index b4540c5cd2a6..b44ca7b6e54f 100644
> > > > > > --- a/sound/pci/hda/hda_intel.c
> > > > > > +++ b/sound/pci/hda/hda_intel.c
> > > > > > @@ -786,7 +786,7 @@ static int azx_acquire_irq(struct azx
> > > > > > *chip,
> > > > > > int do_disconnect)
> > > > > >  	}
> > > > > >  	bus->irq = chip->pci->irq;
> > > > > >  	chip->card->sync_irq = bus->irq;
> > > > > > -	pci_intx(chip->pci, !chip->msi);
> > > > > > +	pcim_intx(chip->pci, !chip->msi);
> > > > > >  	return 0;
> > > > > >  }
> > > > > >  
> > > > > 
> > > > > Hm, it's OK-ish to do this as it's practically same as what
> > > > > pci_intx()
> > > > > currently does.  But, the current code can be a bit
> > > > > inconsistent
> > > > > about
> > > > > the original intx value.  pcim_intx() always stores !enable
> > > > > to
> > > > > res->orig_intx unconditionally, and it means that the
> > > > > orig_intx
> > > > > value
> > > > > gets overridden at each time pcim_intx() gets called.
> > > > 
> > > > Yes.
> > > > 
> > > > > 
> > > > > Meanwhile, HD-audio driver does release and re-acquire the
> > > > > interrupt
> > > > > after disabling MSI when something goes wrong, and pci_intx()
> > > > > call
> > > > > above is a part of that procedure.  So, it can rewrite the
> > > > > res->orig_intx to another value by retry without MSI.  And
> > > > > after
> > > > > the
> > > > > driver removal, it'll lead to another state.
> > > > 
> > > > I'm not sure that I understand this paragraph completely.
> > > > Still,
> > > > could
> > > > a solution for the driver on the long-term just be to use
> > > > pci_intx()?
> > > 
> > > pci_intx() misses the restore of the original value, so it's no
> > > long-term solution, either.
> > 
> > Sure that is missing – I was basically asking whether the driver
> > could
> > live without that feature.
> > 
> > Consider that point obsolete, see below
> > 
> > > 
> > > What I meant is that pcim_intx() blindly assumes the negative of
> > > the
> > > passed argument as the original state, which isn't always true. 
> > > e.g.
> > > when the driver calls it twice with different values, a wrong
> > > value
> > > may be remembered.
> > 
> > Ah, I see – thoguh the issue is when it's called several times with
> > the
> > *same* value, isn't it?
> > 
> > E.g.
> > 
> > pcim_intx(pdev, 1); // 0 is remembered as the old value
> > pcim_intx(pdev, 1); // 0 is falsely remembered as the old value
> > 
> > Also, it would seem that calling the function for the first time
> > like
> > that:
> > 
> > pcim_intx(pdev, 0); // old value: 1
> > 
> > is at least incorrect, because INTx should be 0 per default,
> > shouldn't
> > it? Could then even be a 1st class bug, because INTx would end up
> > being
> > enabled despite having been disabled all the time.
> 
> Yeah, and the unexpected restore can happen even with a single call
> of
> pcim_intx(), if the driver calls it unnecessarily.
> 
> > > That said, I thought of something like below.
> > 
> > At first glance that looks like a good idea to me, thanks for
> > working
> > this out!
> > 
> > IMO you can submit that as a patch so we can discuss it separately.
> 
> Sure, I'm going to submit later.

I just took a look into the old implementation of pci_intx() (there was
no pcim_intx() back then), before I started cleaning up PCI's devres.
This what it looked like before
25216afc9db53d85dc648aba8fb7f6d31f2c8731:

void pci_intx(struct pci_dev *pdev, int enable)
{
	u16 pci_command, new;

	pci_read_config_word(pdev, PCI_COMMAND, &pci_command);

	if (enable)
		new = pci_command & ~PCI_COMMAND_INTX_DISABLE;
	else
		new = pci_command | PCI_COMMAND_INTX_DISABLE;

	if (new != pci_command) {
		struct pci_devres *dr;

		pci_write_config_word(pdev, PCI_COMMAND, new);

		dr = find_pci_dr(pdev);
		if (dr && !dr->restore_intx) {
			dr->restore_intx = 1;
			dr->orig_intx = !enable;
		}
	}
}
EXPORT_SYMBOL_GPL(pci_intx);

If I'm not mistaken the old version did not have the problem because
the value to be restored only changed if new != pci_command.

That should always be correct, what do you think?

If so, only my commit 25216afc9db53d85dc648aba8fb7f6d31f2c8731 needs to
be fixed.

Thanks,
P.


> 
> 
> thanks,
> 
> Takashi
> 

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