linux-kernel - Re: [PATCH v2 1/3] clocksource: tegra: Add nvidia,tegra30-timer compat

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Date:	Wed, 05 Feb 2014 13:17:09 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Andrew Chew <AChew@...dia.com>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"thierry.reding@...il.com" <thierry.reding@...il.com>,
	"rob@...dley.net" <rob@...dley.net>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"robh+dt@...nel.org" <robh+dt@...nel.org>,
	"abrestic@...omium.org" <abrestic@...omium.org>,
	"dgreid@...omium.org" <dgreid@...omium.org>,
	"katierh@...omium.org" <katierh@...omium.org>
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>
Subject: Re: [PATCH v2 1/3] clocksource: tegra: Add nvidia,tegra30-timer compat

On 02/05/2014 01:06 PM, Andrew Chew wrote:
>> On 02/03/2014 05:17 PM, Andrew Chew wrote:
>>> There are some differences between tegra20's timer registers and
>>> tegra30's (and later).  For example, tegra30 has more timers.  In
>>> addition, watchdogs are not present in tegra20.
>>>
>>> Add this compatibility string in order to be able to distinguish
>>> whether the additional timers and watchdogs are there or not.
>>
>>> diff --git a/drivers/clocksource/tegra20_timer.c
>>> b/drivers/clocksource/tegra20_timer.c
>>
>>>  CLOCKSOURCE_OF_DECLARE(tegra20_timer, "nvidia,tegra20-timer",
>>> tegra20_init_timer);
>>> +CLOCKSOURCE_OF_DECLARE(tegra30_timer, "nvidia,tegra30-timer",
>>> +tegra20_init_timer);
>>
>> Thinking about this more, nothing in this driver actually cares about
>> Tegra20 vs. Tegra30+, since the timer that's used is present in all chips.
>> Hence, this patch isn't needed.
> 
> Don't I need to add nvidia,tegra30-timer so that the tegra WDT driver
> can match against it?  It would be weird to have the tegra WDT driver
> bind against nvidia,tegra20-timer when the tegra WDT driver as it is won't
> work at all on tegra20.

The DT files need to contain all of:

* The specific SoC (this is already present)
* nvidia,tegra30-timer for SoCs >= Tegra30 (this is missing)
* nvidia,tegra20-timer for all SoCs (this is already present)

However, since all DTs will contain nvidia,tegra20-timer, since all HW
is backwards-compatible IIUC, any code that only cares about the parts
that have existed since Tegra20 only need match against the Tegra20
compatible value.
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