Re: [PATCH 2/2] clocksource/drivers/fttmr010: Be stricter on IRQs

[Guenter Roeck]

On 8/27/21 3:01 PM, Linus Walleij wrote:
> On Sat, Aug 21, 2021 at 6:20 AM Guenter Roeck <linux@xxxxxxxxxxxx> wrote:
> > On Sun, Jul 25, 2021 at 12:44:24AM +0200, Linus Walleij wrote:
>
> > > Make sure we check that the right interrupt occurred before
> > > calling the event handler for timer 1. Report spurious IRQs
> > > as IRQ_NONE.
> > >
> > > Cc: Cédric Le Goater <clg@xxxxxxxx>
> > > Cc: Joel Stanley <joel@xxxxxxxxx>
> > > Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> >
> > This patch results in boot stalls with several qemu aspeed emulations
> > (quanta-q71l-bmc, palmetto-bmc, witherspoon-bmc, ast2500-evb,
> > romulus-bmc, g220a-bmc). Reverting this patch together with
> > "clocksource/drivers/fttmr010: Clear also overflow bit on AST2600"
> > fixes the problem. Bisect log is attached.
>
> Has it been tested on real hardware?
>
> We are reading register 0x34 TIMER_INTR_STATE for this.
> So this should reflect the state of raw interrupts from the timers.
>
> I looked in qemu/hw/timer/aspeed_timer.c
> and the aspeed_timer_read() looks dubious.
> It rather looks like this falls down to returning whatever
> was written to this register and not reflect which IRQ
> was fired at all.

Actually, no. Turns out the qemu code is just a bit difficult to understand.
The code in question is:

    default:
        value = ASPEED_TIMER_GET_CLASS(s)->read(s, offset);
        break;

For ast2500-evb, that translates to a call to aspeed_2500_timer_read().
Here is a trace example (after adding some more tracing):

aspeed_2500_timer_read From 0x34: 0x0
aspeed_timer_read From 0x34: of size 4: 0x0

Problem is that - at least in qemu - only the 2600 uses register 0x34
for the interrupt status. On the 2500, 0x34 is the ctrl2 register.

Indeed, the patch works fine on, for example, ast2600-evb.
It only fails on ast2400 and ast2500 boards.

I don't have the manuals, so I can't say what the correct behavior is,
but at least there is some evidence that TIMER_INTR_STATE may not exist
on ast2400 and ast2500 SOCs. From drivers/clocksource/timer-fttmr010.c:

/*
 * Interrupt status/mask register definitions for fttmr010/gemini/moxart
 * timers.
 * The registers don't exist and they are not needed on aspeed timers
   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 * because:
 *   - aspeed timer overflow interrupt is controlled by bits in Control
 *     Register (TMC30).
 *   - aspeed timers always generate interrupt when either one of the
 *     Match registers equals to Status register.
 */

Guenter