Re: [PATCH v19 1/7] firmware: arm_rmm: Add SMC definitions for calling the RMM

[Suzuki K Poulose <suzuki.poulose@arm.com>]

On 24/09/2026 18:05, Ackerley Tng wrote:
> Suzuki K Poulose <suzuki.poulose@arm.com> writes:
> 
>>
>> [...snip...]
>>
>> +
>> +/*
>> + * Note many of these fields are smaller than u64 but all fields have u64
>> + * alignment, so use u64 to ensure correct alignment.
>> + */
>> +struct rmm_config {
>> +	union { /* 0x0 */
>> +		struct {
>> +			u64 tracking_region_size;
>> +			u64 rmi_granule_size;
>> +		};
>> +		u8 sizer[SZ_4K];
>> +	};
>> +};
>> +
>> +static_assert(sizeof(struct rmm_config) == SZ_4K);

...

>> +struct realm_params {
>> +	union { /* 0x0 */
>> +		struct {
>> +			u64 flags0;
>> +			u64 s2sz;
>> +			u64 sve_vl;
>> +			u64 num_bps;
>> +			u64 num_wps;
>> +			u64 pmu_num_ctrs;
>> +			u64 hash_algo;
>> +			u64 num_aux_planes;
>> +		};
>> +		u8 padding0[0x400];
> 
> The union + sizer concept is cool. Technically this one isn't a padding,
> it's also a sizer? (same for the other structs below.

Yep, you're right. I have changed all in the file to sizer.

> 
>> +	};

...

>> +};
>> +
>> +static_assert(sizeof(struct realm_params) == SZ_4K);
>> +
> 
> Does declaring this struct as packed matter? I guess the static_assert()
> has the same effect.
> 

I guess it doesn't, the fields are naturally aligned for the offset.
That said, I have added static_assert() for starting offsets for a
a group of related fields to match the spec.

e.g;

static_assert(offsetof(struct realm_params, rpv) == 0x400);
static_assert(offsetof(struct realm_params, rtt_base) == 0x808);
static_assert(offsetof(struct realm_params, aux_rtt_base) == 0xf80);



Thanks for the review !

Suzuki

>>
>> [...snip...]
>>