by Masahiro Yamada

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Subject: Re: [PATCH 1/3] ARM: uniphier: add outer cache support

Hi Linus,

2015-08-26 22:39 GMT+09:00 Linus Walleij <[email protected]>:
> On Mon, Aug 24, 2015 at 4:18 AM, Masahiro Yamada
> <[email protected]> wrote:
>> This commit adds support for UniPhier outer cache controller.
>> All the UniPhier SoCs are equipped with the L2 cache, while the L3
>> cache is currently only integrated on PH1-Pro5 SoC.
>>
>> Signed-off-by: Masahiro Yamada <[email protected]>
>
> Wow it is really a custom L2$ controller. Wow. Just wow. That's
> really brave, given all the problems we've seen in l2x0.

Looks like my company is crazy...
ARM Ltd. people said we are the only vendor that still uses
a custom outer cache.

>> +UniPhier SoCs are integrated with a level 2 cache controller that resides
>> +outside of the ARM cores, some of them also have a level 3 cache controller.
>> +
>> +Required properties:
>> +- compatible: should be one of the followings:
>> + "socionext,uniphier-l2-cache" (L2 cache)
>> + "socionext,uniphier-l3-cache" (L3 cache)
>
> Refer to and use the 3.7.3 ePAPR v1.1 specification too:
> https://www.power.org/wp-content/uploads/2012/06/Power_ePAPR_APPROVED_v1.1.pdf

I've checked it out.
Thanks, but I had some doubts.

> cache-unified and cache-level are *not* optional and should be required.

"cache-unified" is mentioned in "3.7.3 Internal (L1) Cache Properties"
(Table 3-8),
but it is not in "3.8 Multi-level and Shared Caches" (Table 3-9)

Are the rules in Table 3-8 also applied for L2?

> So:
>
>> +The L2 cache must exist to use the L3 cache; adding only an L3 cache device
>> +node to the device tree causes the initialization failure of the whole outer
>> +cache system.
>> +
>> +Example:
>> + l2-cache@500c0000 {
>> + compatible = "socionext,uniphier-l2-cache";
>> + reg = <0x500c0000 0x2000>, <0x503c0100 0x8>,
>> + <0x506c0000 0x400>;
>
> cache-unified;
> cache-level = <2>;
>
>> + /* Not all of UniPhier SoCs have L3 cache */
>> + l3-cache@500c8000 {
>> + compatible = "socionext,uniphier-l3-cache";
>> + reg = <0x500c8000 0x2000>, <0x503c8100 0x8>,
>> + <0x506c8000 0x400>;
>
> cache-unified;
> cache-level = <3>;
>
> (I'm just assuming this cache is unified, anything else would be baffling.)

In fact, unified/harvard is configurable thru a register of this cache
controller.
It is usually used as a unified cached, though.

> Further the ePAPR spec optionally supports specifying things like the
> cache size, number of sets, block size and line size, unless this can
> be hard coded.
>
> Yours,
> Linus Walleij
>

Given that cache-level specifies the level and next-level-cache
specifies the topology,
I think "socionext,uniphier-l*-cache" gives redundant information.

The L2 and L3 cache controller look the same; they have the same register maps.

The differences between them are register-base, cache-size,
cache-sets, line-size,
which are specified by properties.

So,I am planning to use the same compatible for L2 and L3, like this:

l2-cache@500c0000 {
compatible = "socionext,uniphier-cache";
reg = <0x500c0000 0x2000>, <0x503c0100 0x8>,
<0x506c0000 0x400>;
cache-unified;
cache-level = <2>;
next-level-cache = <&L2>;
cache-size = <0x200000>;
cache-sets = <256>;
cache-line-size = <128>;
};

/* Not all of UniPhier SoCs have L3 cache */
l3-cache@500c8000 {
compatible = "socionext,uniphier-cache";
reg = <0x500c8000 0x2000>, <0x503c8100 0x8>,
<0x506c8000 0x400>;
cache-unified;
cache-level = <3>;
cache-size = <0x400000>;
cache-sets = <256>;
cache-line-size = <256>;
};

The Table 3-9 in ePAPR v1.1 says
the compatible should be "cache", but I do not think it makes sense here.

--
Best Regards
Masahiro Yamada