Re: [PATCH 5/7 v6] ARM: l2c: parse 'cache-size' and 'cache-sets' properties

Florian Fainelli
2014-09-08T19:57:34Z

On 09/08/2014 05:36 AM, Linus Walleij wrote:
> On Mon, Sep 8, 2014 at 2:20 PM, Arnd Bergmann <arnd-r2nGTMty4D4@public.gmane.org> wrote:
>> On Monday 08 September 2014 13:38:04 Linus Walleij wrote:
>>> + of_property_read_u32(np, "cache-size", &size);
>>> + of_property_read_u32(np, "cache-sets", &sets);
>>> +
>>> + if (!size || !sets)
>>> + return;
>>> +
>>> + way_size = size / sets;
>>
>> Going back to this one: Isn't (size / sets) the set-size rather
>> than the way-size?
>>
>> After we discussed this on IRC, I had expected a calculation like
>>
>> set_size = size / sets;
>> ways = set_size / line_size;
>> way_size = size / ways;
>
> First: in this PB1176 case:
>
> set_size = 128K/8 = 16K
> ways = 16K/32 = 512 bytes
> way_size = 128K/512 = 128 bytes
>
> Well maybe it's the ARM reference manual internal lingo that
> is actually causing the confusion here. It will say something
> like:
>
> [19:17] Way-size 3’b000 = Reserved, internally mapped to 16KB
> 3’b001 = 16KB, this is the default value
> 3’b010 = 32KB
> 3’b011 = 64KB
> 3’b100 = 128KB
> 3’b101 = 256KB
> 3’b110 to 3’b111 = Reserved, internally mapped to 256 KB
>
> OK way-size ... is in the 16 thru 256KB range, which fits nicely
> with set size incidentally. And also corresponds to current
> comments in the code such as this from
> arch/arm/mach-realview/realview_pb1176.c:
>
> #ifdef CONFIG_CACHE_L2X0
> /*
> * The PL220 needs to be manually configured as the hardware
> * doesn't report the correct sizes.
> * 128kB (16kB/way), 8-way associativity, event monitor and
> * parity enabled, ignore share bit, no force write allocate
> * Bits: .... ...0 0111 0011 0000 .... .... ....
> */
> l2x0_init(__io_address(REALVIEW_PB1176_L220_BASE), 0x00730000,
> 0xfe000fff);
> #endif
>
> I can add a comment explaining that ARMs terminology does
> not match the academic terminology or something, and say that
> the thing we poke into "way-size" is actually "set size", if we agree
> that is what we're seeing here.
>
> Florian: what was your interpretation?

Yes that was my interpretation as well, that we could have 'way-size'
and 'set-size' be the same things here, now that I re-think about it, I
am not sure anymore. More to follow on Arnd's reply to this email.
--
Florian

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