Re: [PATCH] resource: Prevent irqresource_disabled() from erasing flags

[Mika Westerberg <mika.westerberg@linux.intel.com>]

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 :)

> >   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);
>