Re: [PATCH v2] ARM: realview: basic device tree implementation

[Sebastian Hesselbarth <sebastian.hesselbarth-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

On 05/29/2014 04:13 PM, Linus Walleij wrote:
> On Thu, May 29, 2014 at 12:10 PM, Sebastian Hesselbarth
> <sebastian.hesselbarth-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> wrote:
>> On 05/29/2014 11:44 AM, Linus Walleij wrote:
>>> Hmmmm well I want to see that code before I believe it ... but
>>> I get what you mean.
>>
>> Well, the register set on Berlin I was thinking about tackles pinctrl,
>> padmux, clock, reset and some other freaky stuff I cannot recall. The
>> mess in it is that there is no order you can apply to split it up into
>> separate nodes. Moreover, the next SoC has some registers just shoved
>> into it, moving some other registers.
> 
> Berlin hardware engineers seem to be hellbent on complicating
> your life.

Tell me about it! ;)

Although, I don't think it is exclusive to Berlin but other vendors,
too.

>> The way we will go for it on Berlin is now:
>>
>> (a) have a single node for the whole chip-ctrl register set
>> (b) register clk driver on it (early, as it provides timer clk)
>> (c) register one chip-ctrl driver on it that will
>>     (d) reserve the iomap,
>>     (e) register a regmap-mmio,
>>     (f) register platform_devices for {pinctrl,reset,...} that will
>>         use regmap-mmio and read their properties from the single
>>         node
> 
> OK makes perfect sense actually.
> 
>> The individual drivers should stay in their respective drivers/ folder,
>> but (c) needs a good home. It would have been mach-foo in the past, and
>> could be drivers/soc now. In (f), I tend to just lookup regmap by name,
>> no DT involved at all.
> 
> OK
> 
>> BTW, syscon is of no use here at all, once it registers itself as a
>> driver for the node, there will be no other drivers registered. That
>> would at least require (again subsystem driven) dummy-nodes for
>> pinctrl, clk, reset.
> 
> Yeah that sucks, we need something more flexible no question
> about that.
> 
> Will the chipctrl driver be as generic as syscon or a
> Berlin-specific thing?

There is nothing berlin-specific about it except what regmap(s) and
platform_devices are registered. I can think of some generic helpers
to ease looping over regmap structs to be registered, IIRC driver core
already provides the same for platform_devices.

Actually, syscon is already a good starting point, it just lacks to
register platform_devices using the DT-registered regmap.

>> Also, using some of_xlate as we already have for clk, gpio, pinctrl ...
>> would put an end to syscon's syscon_get_regmap_from_{foo,bar,baz,...}
>> that gets a new helper every cycle.
> 
> This part I don't understand but I guess I will understand it
> when I see the code.

git grep 'struct regmap \*syscon' drivers/mfd/syscon.c
drivers/mfd/syscon.c:struct regmap *syscon_node_to_regmap(struct
device_node *np)
drivers/mfd/syscon.c:struct regmap
*syscon_regmap_lookup_by_compatible(const char *s)
drivers/mfd/syscon.c:struct regmap
*syscon_regmap_lookup_by_pdevname(const char *s)
drivers/mfd/syscon.c:struct regmap
*syscon_regmap_lookup_by_phandle(struct device_node *np,

and IIRC I have seen pending patches adding more syscon_regmap_by_foo
helpers.

My point is that we should have some regmap-provider to allow
us to use phandle+specifier, just like of_clk_get and friends work.

With some more time after v3.16-rc1 drops, I plan to provide a
chip-ctrl driver for Berlin. Most likely not too generic or based
on extending syscon but definitely something to talk about.

Sebastian
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