Re: [PATCH v4 1/6] ARM: shmobile: r8a7740 dtsi: Add L2 cache-controller node

[Sudeep Holla <sudeep.holla-5wv7dgnIgG8@public.gmane.org>]

Hi Geert,

On 05/08/15 11:44, Geert Uytterhoeven wrote:
> Hi Sudeep,
>
> On Wed, Aug 5, 2015 at 11:34 AM, Sudeep Holla <sudeep.holla-5wv7dgnIgG8@public.gmane.org> wrote:
>> On 05/08/15 09:58, Geert Uytterhoeven wrote:
>>> Add the missing L2 cache-controller node. This will allow migration to
>>> the generic l2c OF initialization.
>>>
>>> The L2 cache is an ARM L2C-310 (r3p1-150rel0), of size 256 KiB (32 KiB x
>>> 8 ways).
>>>
>>> Signed-off-by: Geert Uytterhoeven <geert+renesas-gXvu3+zWzMSzQB+pC5nmwQ@public.gmane.org>
>
>>> diff --git a/arch/arm/boot/dts/r8a7740.dtsi
>>> b/arch/arm/boot/dts/r8a7740.dtsi
>>> index d84714468cce18df..ddef5b1c68fa06b3 100644
>>> --- a/arch/arm/boot/dts/r8a7740.dtsi
>>> +++ b/arch/arm/boot/dts/r8a7740.dtsi
>>> @@ -37,6 +37,22 @@
>>>                        <0xc2000000 0x1000>;
>>>          };
>>>
>>> +       L2: cache-controller {
>>> +               compatible = "arm,pl310-cache";
>>> +               reg = <0xf0100000 0x1000>;
>>> +               interrupts = <0 84 IRQ_TYPE_LEVEL_HIGH>;
>>> +               power-domains = <&pd_a3sm>;
>>> +               arm,data-latency = <3 3 3>;
>>> +               arm,tag-latency = <2 2 2>;
>>> +               arm,shared-override;
>>> +               cache-unified;
>>> +               cache-level = <2>;
>>> +               cache-size = <0x40000>;
>>> +               cache-sets = <1024>;
>>> +               cache-block-size = <32>;
>>> +               cache-line-size = <32>;
>>
>>
>> Any particular reason whey you need all this cache-* properties ? Is
>
> To describe the cache as good as possible.
>

Why if you can probe it ? IMO DT is mostly useful to describe things
that can't be probed/discovered using hardware.

>> something broken on these SoCs ? We should be able to get most of these
>> information from the SoC(reading some registers). It's good to avoid
>> passing them via DT if they can be discovered from hardware.
>
> So we have all these documented properties in
> Documentation/devicetree/bindings/arm/l2cc.txt, but they're not meant to
> be used?
>

No I didn't mean that, I just wanted to know if they can't be probed due
to some hardware issue. It would avoid issues with wrong DTs especially
if they are not so easy to upgrade.

Regards,
Sudeep
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