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

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Date:	Wed, 5 Feb 2014 13:39:37 -0800
From:	Andrew Chew <AChew@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>,
	"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.

Okay, I think I get what you're saying.  So I'll drop this patch.  The tegra WDT
driver will still match against nvidia,tegra30-timer, and device trees for SoCs
that expect to use this WDT driver will have to have nvidia,tegra30-timer.
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