linux-kernel - Re: [PATCH v2 2/3] clocksource: tegra: Define timer bases in header file

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Date:	Wed, 05 Feb 2014 13:03:47 -0700
From:	Stephen Warren <swarren@...dotorg.org>
To:	Andrew Chew <achew@...dia.com>, daniel.lezcano@...aro.org,
	tglx@...utronix.de, thierry.reding@...il.com, rob@...dley.net,
	grant.likely@...aro.org, robh+dt@...nel.org, abrestic@...omium.org,
	dgreid@...omium.org, katierh@...omium.org
CC:	linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
	linux-watchdog@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v2 2/3] clocksource: tegra: Define timer bases in header
 file

On 02/03/2014 05:17 PM, Andrew Chew wrote:
> Added timers that are present in tegra30 and later, that are NOT in tegra20.
> 
> Also, some of these timer bases are needed in the tegra watchdog driver, so
> separate them out into a header file that both the clocksource driver and
> the watchdog driver can share them.

> diff --git a/include/clocksource/tegra_timer.h b/include/clocksource/tegra_timer.h

> +/* Tegra 20 timers */
> +#define TEGRA20_TIMER1_BASE	0x0
> +#define TEGRA20_TIMER2_BASE	0x8
> +#define TEGRA20_TIMER3_BASE	0x50
> +#define TEGRA20_TIMER4_BASE	0x58
> +
> +/* Tegra 30 timers */
> +#define TEGRA30_TIMER1_BASE	TEGRA20_TIMER1_BASE
> +#define TEGRA30_TIMER2_BASE	TEGRA20_TIMER2_BASE
> +#define TEGRA30_TIMER3_BASE	TEGRA20_TIMER3_BASE
> +#define TEGRA30_TIMER4_BASE	TEGRA20_TIMER4_BASE
> +#define TEGRA30_TIMER5_BASE	0x60
> +#define TEGRA30_TIMER6_BASE	0x68
> +#define TEGRA30_TIMER7_BASE	0x70
> +#define TEGRA30_TIMER8_BASE	0x78
> +#define TEGRA30_TIMER9_BASE	0x80
> +#define TEGRA30_TIMER0_BASE	0x88

Why put the SoC name in the define names? Why not just have
TIMER1_BASE..TIMER10_BASE (that should be 10 not 0 as in your patch,
right?) and have the driver know that 1..4 are valid on Tegra20, and
1..10 are valid on later chips.

I guess if the defines are moved into a header file, adding a TEGRA_
prefix does make sense.

But I wonder if it wouldn't be simpler for the Tegra WDT driver to just
call a function on the Tegra clocksource driver to find out which timer
ID(s) to avoid using? Even simpler would be to just put a comment in the
WDT driver saying that timer 5 was chosen arbitrarily, but if it's
changed make sure not to conflict with the clocksource driver (and an
equivalent change to the clocksource driver).
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