Re: [PATCH 25/52] m68k: apollo: Replace set but not used variable by READ_ONCE()

[Arnd Bergmann]

On Fri, Sep 8, 2023, at 08:51, Geert Uytterhoeven wrote:
>
> On Fri, Sep 8, 2023 at 1:37 AM Finn Thain <fthain@xxxxxxxxxxxxxx> wrote:
>> On Thu, 7 Sep 2023, Geert Uytterhoeven wrote:
>> > --- a/arch/m68k/apollo/config.c
>> > +++ b/arch/m68k/apollo/config.c
>> > @@ -146,13 +146,11 @@ void __init config_apollo(void)
>> >
>> >  irqreturn_t dn_timer_int(int irq, void *dev_id)
>> >  {
>> > -     volatile unsigned char x;
>> > -
>> >       legacy_timer_tick(1);
>> >       timer_heartbeat();
>> >
>> > -     x = *(volatile unsigned char *)(apollo_timer + 3);
>> > -     x = *(volatile unsigned char *)(apollo_timer + 5);
>> > +     READ_ONCE(*(volatile unsigned char *)(apollo_timer + 3));
>> > +     READ_ONCE(*(volatile unsigned char *)(apollo_timer + 5));
>> >
>> >       return IRQ_HANDLED;
>> >  }
>> >
>>
>> I believe the volatile cast is redundant here, as READ_ONCE does that.
>
> Yes it does.  I didn't drop the volatile out of fear of introducing
> some higher W-level warning about casting away volatility, but upon
> closer look, the apollo_timer definition itself does not use volatile.

I think ideally you'd want apollo_timer or IO_BASE to be marked __iomem
and passed to readb() instead. OTOH, I don't think anyone actually
cares about apollo, so your version is probably good enough.

     Arnd