[PATCH] drm/panfrost: Update io-pgtable API

[Robin Murphy]

On 2022-08-23 03:51, Alyssa Rosenzweig wrote:
>> -static size_t get_pgsize(u64 addr, size_t size)
>> +static size_t get_pgsize(u64 addr, size_t size, size_t *count)
>>   {
>> -	if (addr & (SZ_2M - 1) || size < SZ_2M)
>> -		return SZ_4K;
>> +	size_t blk_offset = -addr % SZ_2M;
> 
> addr is unsigned. if this is correct, it's magic.

Eh, it's just well-defined unsigned integer overflow. Take "SZ_2M - 
(addr % SZ_2M)", realise the first term can be anything that's zero 
modulo SZ_2M, including zero, then also that the operations can be done 
in either order to give the same result, and there you go.

Cheers,
Robin.