[PATCH 1/2] lib: utils: Implement "64bit-mmio" property parsing

[Jessica Clarke]

On 17 Apr 2021, at 15:24, Guo Ren <guoren at kernel.org> wrote:
> 
> On Sat, Apr 17, 2021 at 7:45 PM Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>> 
>> On 17 Apr 2021, at 12:41, Jessica Clarke <jrtc27 at jrtc27.com> wrote:
>>> 
>>> On 13 Apr 2021, at 04:44, guoren at kernel.org wrote:
>>>> 
>>>> From: Guo Ren <guoren at linux.alibaba.com>
>>>> 
>>>> Figure out CLINT has_64bit_mmio from DT node and using antonym for
>>>> compatibility.
>>>> 
>>>> Signed-off-by: Guo Ren <guoren at linux.alibaba.com>
>>>> Cc: Anup Patel <anup.patel at wdc.com>
>>>> Cc: Xiang W <wxjstz at 126.com>
>>>> ---
>>>> lib/utils/fdt/fdt_helper.c | 3 ++-
>>>> 1 file changed, 2 insertions(+), 1 deletion(-)
>>>> 
>>>> diff --git a/lib/utils/fdt/fdt_helper.c b/lib/utils/fdt/fdt_helper.c
>>>> index bf19ff9..909de01 100644
>>>> --- a/lib/utils/fdt/fdt_helper.c
>>>> +++ b/lib/utils/fdt/fdt_helper.c
>>>> @@ -442,8 +442,9 @@ int fdt_parse_clint_node(void *fdt, int nodeoffset, bool for_timer,
>>>>     if (clint->hart_count < count)
>>>>             clint->hart_count = count;
>>>> 
>>>> -    /* TODO: We should figure-out CLINT has_64bit_mmio from DT node */
>>>>     clint->has_64bit_mmio = TRUE;
>>>> +    if (fdt_getprop(fdt, nodeoffset, "clint,has-no-64bit-mmio", &count))
>>> 
>>> I do not see this specified in clint.yaml.
>> 
>> Also, the RISC-V privileged is very clear:
>> 
>>> For RV64, naturally aligned 64-bit memory accesses to the mtime and mtimecmp
>>> registers are atomic.
>> 
>> So I would say your CLINT violates the spec and thus should not claim to be a
>> RISC-V or SiFive-compatible CLINT.
>> 
>> Jess
>> 
> 
> Normal Linux use csr_read(CSR_TIME), and C9xx wouldn't support
> M-mode&MMU-less Linux. So the only sbi_set_timer would be affected.
> 
> Because mmio-32bit is perfect with RV32, it wouldn't cause problems in
> the RV64 linux mmu s-mode system.

That doesn’t change the fact that it violates the spec for RV64.

Jess