linux-kernel - Re: [RFC PATCH] irqchip/gic-v3-its: apply ACPI device based quirks

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Message-ID: <CAKv+Gu_Em_QFpGeRWra0uBxOm7rbhc12waxhCRd5tmRyqt1yrg@mail.gmail.com>
Date:   Mon, 26 Feb 2018 11:09:30 +0000
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Marc Zyngier <marc.zyngier@....com>
Cc:     linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Graeme Gregory <graeme.gregory@...aro.org>,
        Jason Cooper <jason@...edaemon.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC PATCH] irqchip/gic-v3-its: apply ACPI device based quirks

On 26 February 2018 at 10:18, Marc Zyngier <marc.zyngier@....com> wrote:
> Hi Ard,
>
> On 13/02/18 14:11, Ard Biesheuvel wrote:
>> Reapply the SynQuacer quirk for ITS frames that are matched by 'SCX0005'
>> based ACPI devices, replacing the dummy fwnode with the one populated by
>> the ACPI device core.
>>
>> This allows the SynQuacer ACPI tables to publish a device node such
>> as
>>
>>     Device (ITS0) {
>>       Name (_HID, "SCX0005")
>>       Name (_ADR, 0x30020000)
>>       Name (_DSD, Package ()  // _DSD: Device-Specific Data
>>       {
>>         ToUUID ("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
>>         Package () {
>>           Package (2) {
>>             "socionext,synquacer-pre-its",
>>             Package () { 0x58000000, 0x200000 }
>>           },
>>         }
>>       })
>>     }
>>
>> which will trigger the existing quirk that replaces the doorbell
>> address with the appropriate address in the pre-ITS frame.
>>
>> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
>> ---
>> Marc, Lorenzo,
>>
>> I am aware that this patch may be seen as controversial, but I would like to
>> propose it nonetheless. The reason is that this is the only thing standing in
>> the way of full ACPI support in Socionext SynQuacer based platforms.
>>
>> The pre-ITS is a monstrosity, but as it turns out, Socionext had help from
>> ARM designing it, and the reason we need DT/ACPI based quirks in the first
>> place is that the IIDR of this GICv3 implementation is simply the ARM Ltd.
>> one (as they designed the IP)
>
> That's odd. A bit of archaeology shows that ARM indeed designed a
> pre-ITS, but that one doesn't break isolation at all (it still has a
> single doorbell). So whatever creative changes Socionext applied to that
> piece of IP (assuming this is the same IP), they didn't really
> understand the far reaching impact it has.
>

OK, thanks for digging that up. All the information I have on this
topic is second hand, and I had no reason to assume their account of
the history was inaccurate.

>>
>> Please take this into consideration when reviewing this patch,
>>
>> Thanks,
>> Ard.
>>
>>  drivers/irqchip/irq-gic-v3-its.c | 39 ++++++++++++++++++++
>>  1 file changed, 39 insertions(+)
>>
>> diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
>> index 06f025fd5726..a63973baf08a 100644
>> --- a/drivers/irqchip/irq-gic-v3-its.c
>> +++ b/drivers/irqchip/irq-gic-v3-its.c
>> @@ -3517,3 +3517,42 @@ int __init its_init(struct fwnode_handle *handle, struct rdists *rdists,
>>
>>       return 0;
>>  }
>> +
>> +#if defined(CONFIG_SOCIONEXT_SYNQUACER_PREITS) && defined(CONFIG_ACPI)
>> +static acpi_status __init acpi_its_device_probe (acpi_handle handle,
>> +                                              u32 depth, void *context,
>> +                                              void **ret)
>> +{
>> +     struct acpi_device *adev;
>> +     unsigned long long phys_base;
>> +     struct its_node *its;
>> +     acpi_status status;
>> +     int err;
>> +
>> +     err = acpi_bus_get_device(handle, &adev);
>> +     if (err)
>> +             return AE_CTRL_TERMINATE;
>> +
>> +     status = acpi_evaluate_integer(handle, "_ADR", NULL, &phys_base);
>> +     if (ACPI_FAILURE(status))
>> +             return status;
>> +
>> +     list_for_each_entry(its, &its_nodes, entry)
>> +             if (its->phys_base == phys_base) {
>> +                     irq_domain_free_fwnode(its->fwnode_handle);
>
> That line scares me. What about irq domains that are hold a pointer to
> this handle? its_init_domain() uses it to construct the LPI domain, and
> it is now pointing to some free memory.
>
> You'd need to reassign all the domains that match this fwnode before
> freeing it.
>

OK, I can iterate over the domains using irq_find_matching_fwspec()
and update the handles one by one. Not pretty, but that is a lost
cause anyway for this patch.

>> +                     its->fwnode_handle = &adev->fwnode;
>> +                     its_enable_quirk_socionext_synquacer(its);
>> +                     break;
>> +             }
>> +
>> +     return AE_CTRL_TERMINATE;
>> +}
>> +
>> +static int __init acpi_its_device_probe_init(void)
>> +{
>> +     if (!acpi_disabled)
>> +             acpi_get_devices("SCX0005", acpi_its_device_probe, NULL, NULL);
>> +     return 0;
>> +}
>> +subsys_initcall_sync(acpi_its_device_probe_init);
>> +#endif
>>
>
> Is there any chance that MSIs could be allocated before this kicks in?
> If that happens, we're in trouble...

This SoC does not have any MSI capable platform devices, so the only
consumers are PCI devices, and PCI drivers are registered as a
device_initcal().