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Message-ID: <525433D3.2090906@free-electrons.com>
Date: Tue, 08 Oct 2013 18:33:23 +0200
From: Gregory CLEMENT <gregory.clement@...e-electrons.com>
To: Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
CC: Mark Rutland <mark.rutland@....com>,
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>
Subject: Re: [PATCH 3/8] ARM: l2x0: add Marvell Tauros3 compatible
On 08/10/2013 18:05, Sebastian Hesselbarth wrote:
> 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.
I agree with Sebastian. I don't have more information that Sebastian, but
as it is definitely a different controller of the ones from ARM, it should
have its own compatible string. Then latter when we will discover new feature
and/or bugs, we will be able to manage them without requiring people to update
their dtb. If I understood well it is the philosophy behind the device tree.
Regards,
>
> But again, I am very open for suggestions here.
>
> Sebastian
>
--
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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