Messages in this thread | | | From | David Brownell <> | Subject | Re: Get rid of IRQF_DISABLED - (was [PATCH] genirq: warn about IRQF_SHARED|IRQF_DISABLED) | Date | Mon, 30 Nov 2009 12:53:28 -0800 |
| |
On Monday 30 November 2009, Russell King - ARM Linux wrote: > On Mon, Nov 30, 2009 at 02:47:02PM +0000, Alan Cox wrote: > > SHARED|DISABLED ought to WARN_ON() and if that doesn't motivate people > > then return -EINVAL. > > That is an impossibility. There is hardware out there (AT91) where > the timer interrupt is shared with other peripherals, and you end > up with a mixture of irqs-disabled and irqs-enabled handlers sharing > the same interrupt.
For the record: AT91 isn't restricted to the system timers hooked up on irq 0 ... there's also drivers/clocksource/tcb_clksrc.c (not at the same hardware priority).
But to concur, this is indeed messy. Both the system timer and the serial console generally share the same IRQ; both are very timing-sensitive. I've seen console character dropouts after tweaking timer IRQ handling. And I've never convinced myself that Linux handles the hardware IRQ priority on those chips as well as it could.
> My point is that if we outlaw irqs-disabled shared interrupts, it puts > Atmel AT91 support into immediate difficulties.
ISTR that those TCB modules don't share IRQs with other peripherals.
Also, that Linux doesn't use them for much else. I've yet to see a three-phase motor driver using the TCB's PWM capabilities, for example.
- Dave
| |