linux-kernel - Re: [PATCH 3/8] ARM: l2x0: add Marvell Tauros3 compatible

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Date:	Tue, 08 Oct 2013 18:05:56 +0200
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	Mark Rutland <mark.rutland@....com>
CC:	Jason Cooper <jason@...edaemon.net>,
	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Arnd Bergmann <arnd@...db.de>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Gregory CLEMENT <gregory.clement@...e-electrons.com>
Subject: Re: [PATCH 3/8] ARM: l2x0: add Marvell Tauros3 compatible

On 10/08/2013 03:41 PM, Mark Rutland wrote:
> On Tue, Oct 08, 2013 at 01:24:28PM +0100, Sebastian Hesselbarth wrote:
>> This add a compatible for the Marvell Tauros3 cache controller which
>> is compatible with l2x0 cache controllers. While updating the binding
>> documentation, clean up the list of possible compatibles.
>>
>> Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
>> ---
[...]
>> diff --git a/Documentation/devicetree/bindings/arm/l2cc.txt b/Documentation/devicetree/bindings/arm/l2cc.txt
>> index c0c7626..a1d0cbd 100644
>> --- a/Documentation/devicetree/bindings/arm/l2cc.txt
>> +++ b/Documentation/devicetree/bindings/arm/l2cc.txt
>> @@ -7,20 +7,20 @@ The ARM L2 cache representation in the device tree should be done as follows:
>>   Required properties:
>>
>>   - compatible : should be one of:
>> -	"arm,pl310-cache"
>> -	"arm,l220-cache"
>> -	"arm,l210-cache"
>> -	"marvell,aurora-system-cache": Marvell Controller designed to be
>> +  "arm,pl310-cache"
>> +  "arm,l220-cache"
>> +  "arm,l210-cache"
>> +  "bcm,bcm11351-a2-pl310-cache": DEPRECATED by "brcm,bcm11351-a2-pl310-cache"
>> +  "brcm,bcm11351-a2-pl310-cache": For Broadcom bcm11351 chipset where an
>> +     offset needs to be added to the address before passing down to the L2
>> +     cache controller
>> +  "marvell,aurora-system-cache": Marvell Controller designed to be
>>        compatible with the ARM one, with system cache mode (meaning
>>        maintenance operations on L1 are broadcasted to the L2 and L2
>>        performs the same operation).
>> -	"marvell,"aurora-outer-cache: Marvell Controller designed to be
>> -	 compatible with the ARM one with outer cache mode.
>> -	"brcm,bcm11351-a2-pl310-cache": For Broadcom bcm11351 chipset where an
>> -	offset needs to be added to the address before passing down to the L2
>> -	cache controller
>> -	"bcm,bcm11351-a2-pl310-cache": DEPRECATED by
>> -	                               "brcm,bcm11351-a2-pl310-cache"
>> +  "marvell,aurora-outer-cache": Marvell Controller designed to be
>> +     compatible with the ARM one with outer cache mode.
>> +  "marvell,tauros3-cache": Marvell Tauros3 cache controller.
>
> How does the tauros3 cache differ from the other caches supported by the
> l2x0 driver?

[added Gregory to Cc]

Good question. I cannot say at this time. I would have guessed that l2cc
on Armada 1500 and Armada 370/XP are more or less the same, as both use
Marvell's PJ4B CPU. Maybe, Gregory or Thomas can shed some light into
this.

>>   - cache-unified : Specifies the cache is a unified cache.
>>   - cache-level : Should be set to 2 for a level 2 cache.
>>   - reg : Physical base address and size of cache controller's memory mapped
>> diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c
>> index 447da6f..90c776e 100644
>> --- a/arch/arm/mm/cache-l2x0.c
>> +++ b/arch/arm/mm/cache-l2x0.c
>> @@ -929,6 +929,7 @@ static const struct of_device_id l2x0_ids[] __initconst = {
>>   	  .data = (void *)&aurora_no_outer_data},
>>   	{ .compatible = "marvell,aurora-outer-cache",
>>   	  .data = (void *)&aurora_with_outer_data},
>> +	{ .compatible = "marvell,tauros3-cache", .data = (void *)&l2x0_data },
>
> Are we intending to handle this differently later?
>
> Or is it 100% compatible with the pl210 or pl220? We could just require
> an entry later in the compatible string list instead...

No public documentation, no clear answer.

Tauros3 isn't 100% compatible with any of the ARM l2cc above, it has
additional "features" or "bugs" - call it whatever you want.

I am not an l2cc expert, but basically I see two options:
a) use (possibly) wrong existing compatible in current mv88de3100.dtsi
    now and fix later.
b) add tauros3 compatible now and add (possible) quirks/marvell-specific
    properties later.

IMHO b) is very likely to happen as l2x0_of_init in patch 8/8 already 
sets bits, I wasn't able to verify in public ARM l2cc docu.

But again, I am very open for suggestions here.

Sebastian
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