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Subject: Re: [PATCH] resource: Prevent irqresource_disabled() from erasing
 flags
To:     Angela Czubak <acz@semihalf.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>
Cc:     akpm@linux-foundation.org, john.garry@huawei.com,
        linux-kernel@vger.kernel.org, upstream@semihalf.com,
        dtor@chromium.org, linux-acpi <linux-acpi@intel.com>,
        rafael@kernel.org
References: <20210329195238.9455-1-acz@semihalf.com>
From:   "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>
Organization: Intel Technology Poland Sp. z o. o., KRS 101882, ul. Slowackiego
 173, 80-298 Gdansk
Message-ID: <1c086b9e-d5c2-6e8d-1d81-748935b0dd64@intel.com>
Date:   Tue, 30 Mar 2021 17:09:42 +0200
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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?


>   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);