Re: [PATCH V2] arm64/cpufeature: Add get_arm64_ftr_reg_nowarn()

Anshuman Khandual
2020-05-27T02:27:20Z

On 05/27/2020 01:16 AM, Will Deacon wrote:
> On Tue, May 26, 2020 at 04:01:35PM +0100, Catalin Marinas wrote:
>> On Tue, May 26, 2020 at 07:09:13PM +0530, Anshuman Khandual wrote:
>>> @@ -632,8 +654,6 @@ static void __init init_cpu_ftr_reg(u32 sys_reg, u64 new)
>>> const struct arm64_ftr_bits *ftrp;
>>> struct arm64_ftr_reg *reg = get_arm64_ftr_reg(sys_reg);
>>>
>>> - BUG_ON(!reg);
>>> -
>>> for (ftrp = reg->ftr_bits; ftrp->width; ftrp++) {
>>> u64 ftr_mask = arm64_ftr_mask(ftrp);
>>> s64 ftr_new = arm64_ftr_value(ftrp, new);
>>> @@ -762,7 +782,6 @@ static int check_update_ftr_reg(u32 sys_id, int cpu, u64 val, u64 boot)
>>> {
>>> struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id);
>>>
>>> - BUG_ON(!regp);
>>> update_cpu_ftr_reg(regp, val);
>>> if ((boot & regp->strict_mask) == (val & regp->strict_mask))
>>> return 0;
>>> @@ -776,9 +795,6 @@ static void relax_cpu_ftr_reg(u32 sys_id, int field)
>>> const struct arm64_ftr_bits *ftrp;
>>> struct arm64_ftr_reg *regp = get_arm64_ftr_reg(sys_id);
>>>
>>> - if (WARN_ON(!regp))
>>> - return;
>>
>> I think Will wanted an early return in all these functions not just
>> removing the BUG_ON(). I'll let him clarify.
>
> Yes, the callers need to check the pointer and return early.

Sure, will do. But for check_update_ftr_reg(), a feature register search
failure should be treated as a success (0) or a failure (1). What should
it return ? Seems bit tricky, as there are good reasons to go either way.