Re: [PATCH 2/4] hw/intc: sifive_plic.c: Fix interrupt priority index.

[Jim Shu <jim.shu@sifive.com>]

Hi Tyler,

This fix is incorrect.

In PLIC spec, Interrupt Source Priority Memory Map is
0x000000: Reserved (interrupt source 0 does not exist)
0x000004: Interrupt source 1 priority
0x000008: Interrupt source 2 priority

Current RISC-V machines (virt, sifive_u) use 0x4 as priority_base, so
current formula "irq = ((addr - plic->priority_base) >> 2) + 1" will
take offset 0x4 as IRQ source 1, which is correct.
Your fix will cause the bug in existing machines.

Thanks,
Jim Shu




On Tue, Sep 6, 2022 at 11:21 PM Tyler Ng <tkng@rivosinc.com> wrote:
>
> Here's the patch SHA that introduced the offset: 0feb4a7129eb4f120c75849ddc9e50495c50cb63
>
> -Tyler
>
> On Mon, Sep 5, 2022 at 6:15 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>>
>> On Thu, Sep 01, 2022 at 03:50:06PM -0700, Tyler Ng wrote:
>> > Fixes a bug in which the index of the interrupt priority is off by 1.
>> > For example, using an IRQ number of 3 with a priority of 1 is supposed to set
>> > plic->source_priority[2] = 1, but instead it sets
>> > plic->source_priority[3] = 1. When an interrupt is claimed to be
>> > serviced, it checks the index 2 instead of 3.
>> >
>> > Signed-off-by: Tyler Ng <tkng@rivosinc.com>
>>
>> Fixes tag?
>>
>> Thanks,
>> drew
>>
>> > ---
>> >  hw/intc/sifive_plic.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> >
>> > diff --git a/hw/intc/sifive_plic.c b/hw/intc/sifive_plic.c
>> > index af4ae3630e..e75c47300a 100644
>> > --- a/hw/intc/sifive_plic.c
>> > +++ b/hw/intc/sifive_plic.c
>> > @@ -178,7 +178,7 @@ static void sifive_plic_write(void *opaque, hwaddr
>> > addr, uint64_t value,
>> >      SiFivePLICState *plic = opaque;
>> >
>> >      if (addr_between(addr, plic->priority_base, plic->num_sources << 2)) {
>> > -        uint32_t irq = ((addr - plic->priority_base) >> 2) + 1;
>> > +        uint32_t irq = ((addr - plic->priority_base) >> 2) + 0;
>> >
>> >          plic->source_priority[irq] = value & 7;
>> >          sifive_plic_update(plic);
>> > --
>> > 2.30.2
>> >