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SubjectRe: [RFC PATCH v4 2/2] arm64: tlb: Use the TLBI RANGE feature in arm64
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On 2020-07-07 18:46, Catalin Marinas wrote:
> On Tue, Jul 07, 2020 at 06:43:35PM +0100, Marc Zyngier wrote:
>> On 2020-07-07 18:36, Catalin Marinas wrote:
>>> On Mon, Jun 01, 2020 at 10:47:13PM +0800, Zhenyu Ye wrote:
>>>> @@ -59,6 +69,47 @@
>>>> __ta; \
>>>> })
>>>>
>>>> +/*
>>>> + * __TG defines translation granule of the system, which is decided
>>>> by
>>>> + * PAGE_SHIFT. Used by TTL.
>>>> + * - 4KB : 1
>>>> + * - 16KB : 2
>>>> + * - 64KB : 3
>>>> + */
>>>> +#define __TG ((PAGE_SHIFT - 12) / 2 + 1)
>>>
>>> Nitpick: maybe something like __TLBI_TG to avoid clashes in case someone
>>> else defines a __TG macro.
>>
>> I have commented on this in the past, and still maintain that this
>> would be better served by a switch statement similar to what is used
>> for TTL already (I don't think this magic formula exists in the
>> ARM ARM).
>
> Good point, it would be cleaner indeed.

FWIW, we use the somewhat obtuse "(shift - 10) / 2" in the SMMUv3
driver, but that's because we support multiple different granules at
runtime and want to generate efficient code. Anything based on
PAGE_SHIFT that resolves to a compile-time constant has no excuse for
not being written in a clear and obvious manner ;)

Robin.

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