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From:   Angela Czubak <acz@semihalf.com>
Date:   Wed, 7 Apr 2021 13:01:10 +0200
Message-ID: <CAB4aORU9N9684j4eqKPUx7s5NrfO_37=EmR3JoSPaA4RvY87OQ@mail.gmail.com>
Subject: Re: [PATCH] resource: Prevent irqresource_disabled() from erasing flags
To:     Mika Westerberg <mika.westerberg@linux.intel.com>
Cc:     "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        akpm@linux-foundation.org, john.garry@huawei.com,
        linux-kernel@vger.kernel.org, upstream@semihalf.com,
        Dmitry Torokhov <dtor@chromium.org>,
        linux-acpi <linux-acpi@intel.com>, rafael@kernel.org
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On Tue, Mar 30, 2021 at 5:50 PM Mika Westerberg
<mika.westerberg@linux.intel.com> wrote:
>
> Hi,
>
> On Tue, Mar 30, 2021 at 05:09:42PM +0200, Rafael J. Wysocki wrote:
> > On 3/29/2021 9:52 PM, Angela Czubak wrote:
> > > Do not overwrite flags as it leads to erasing triggering and polarity
> > > information which might be useful in case of hard-coded interrupts.
> > > This way the information can be read later on even though mapping to
> > > APIC domain failed.
> > >
> > > Signed-off-by: Angela Czubak <acz@semihalf.com>
> > > ---
> > > Some Chromebooks use hard-coded interrupts in their ACPI tables.
> > > This is an excerpt as dumped on Relm:
> > >
> > > ...
> > >              Name (_HID, "ELAN0001")  // _HID: Hardware ID
> > >              Name (_DDN, "Elan Touchscreen ")  // _DDN: DOS Device Name
> > >              Name (_UID, 0x05)  // _UID: Unique ID
> > >              Name (ISTP, Zero)
> > >              Method (_CRS, 0, NotSerialized)  // _CRS: Current Resource Settings
> > >              {
> > >                  Name (BUF0, ResourceTemplate ()
> > >                  {
> > >                      I2cSerialBusV2 (0x0010, ControllerInitiated, 0x00061A80,
> > >                          AddressingMode7Bit, "\\_SB.I2C1",
> > >                          0x00, ResourceConsumer, , Exclusive,
> > >                          )
> > >                      Interrupt (ResourceConsumer, Edge, ActiveLow, Exclusive, ,, )
> > >                      {
> > >                          0x000000B8,
> > >                      }
> > >                  })
> > >                  Return (BUF0) /* \_SB_.I2C1.ETSA._CRS.BUF0 */
> > >              }
> > > ...
> > >
> > > This interrupt is hard-coded to 0xB8 = 184 which is too high to be mapped
> > > to IO-APIC, so no triggering information is propagated as acpi_register_gsi()
> > > fails and irqresource_disabled() is issued, which leads to erasing triggering
> > > and polarity information.
> > > If that function added its flags instead of overwriting them the correct IRQ
> > > type would be set even for the hard-coded interrupts, which allows device driver
> > > to retrieve it.
> > > Please, let me know if this kind of modification is acceptable.
> >
> > From the quick look it should not be problematic, but it needs to be checked
> > more carefully.
> >
> > Mika, what do you think?
>
> I think it makes sense. We still set IORESOURCE_DISABLED unconditionally
> so this should not cause issues. In theory at least :)
>
Is there anything else you would need me to do regarding the patch?
I suppose there are more platforms that could benefit from not erasing
the flags, so if this patch is fit for upstream, can we continue the
process?

> > >   include/linux/ioport.h | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/include/linux/ioport.h b/include/linux/ioport.h
> > > index 55de385c839cf..647744d8514e0 100644
> > > --- a/include/linux/ioport.h
> > > +++ b/include/linux/ioport.h
> > > @@ -331,7 +331,7 @@ static inline void irqresource_disabled(struct resource *res, u32 irq)
> > >   {
> > >     res->start = irq;
> > >     res->end = irq;
> > > -   res->flags = IORESOURCE_IRQ | IORESOURCE_DISABLED | IORESOURCE_UNSET;
> > > +   res->flags |= IORESOURCE_IRQ | IORESOURCE_DISABLED | IORESOURCE_UNSET;
> > >   }
> > >   extern struct address_space *iomem_get_mapping(void);
> >