x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines

x86/apic: Fix arch_dynirq_lower_bound() bug for DT enabled machines

[ Upstream commit 3e5bedc2c258341702ddffbd7688c5e6eb01eafa ]

Rahul Tanwar reported the following bug on DT systems:

> 'ioapic_dynirq_base' contains the virtual IRQ base number. Presently, it is
> updated to the end of hardware IRQ numbers but this is done only when IOAPIC
> configuration type is IOAPIC_DOMAIN_LEGACY or IOAPIC_DOMAIN_STRICT. There is
> a third type IOAPIC_DOMAIN_DYNAMIC which applies when IOAPIC configuration
> comes from devicetree.
>
> See dtb_add_ioapic() in arch/x86/kernel/devicetree.c
>
> In case of IOAPIC_DOMAIN_DYNAMIC (DT/OF based system), 'ioapic_dynirq_base'
> remains to zero initialized value. This means that for OF based systems,
> virtual IRQ base will get set to zero.

Such systems will very likely not even boot.

For DT enabled machines ioapic_dynirq_base is irrelevant and not
updated, so simply map the IRQ base 1:1 instead.

Reported-by: Rahul Tanwar <rahul.tanwar@linux.intel.com>
Tested-by: Rahul Tanwar <rahul.tanwar@linux.intel.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: alan@linux.intel.com
Cc: bp@alien8.de
Cc: cheol.yong.kim@intel.com
Cc: qi-ming.wu@intel.com
Cc: rahul.tanwar@intel.com
Cc: rppt@linux.ibm.com
Cc: tony.luck@intel.com
Link: http://lkml.kernel.org/r/20190821081330.1187-1-rahul.tanwar@linux.intel.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>