linux-kernel - Re: [PATCH 1/3] ARM: tegra: Add AHB driver

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Date:	Mon, 23 Apr 2012 12:33:09 +0000
From:	Arnd Bergmann <arnd@...db.de>
To:	Hiroshi DOYU <hdoyu@...dia.com>
Cc:	linux-tegra@...r.kernel.org, Colin Cross <ccross@...roid.com>,
	Olof Johansson <olof@...om.net>,
	Stephen Warren <swarren@...dotorg.org>,
	Russell King <linux@....linux.org.uk>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] ARM: tegra: Add AHB driver

On Monday 23 April 2012, Hiroshi DOYU wrote:
> The AHB Bus conforms to the AMBA Specification (Rev 2.0) Advanced
> High-performance Bus (AHB) architecture.
> 
> Both Tegra20/30 have this.
> 
> Signed-off-by: Hiroshi DOYU <hdoyu@...dia.com>

Please explain in the text above why it's a good idea to have this
driver.


> @@ -122,6 +123,7 @@ void __init tegra20_init_early(void)
>  	tegra_init_cache(0x331, 0x441);
>  	tegra_pmc_init();
>  	tegra_powergate_init();
> +	tegra_ahb_gizmo_init();
>  }
>  #endif
>  #ifdef CONFIG_ARCH_TEGRA_3x_SOC
> @@ -132,5 +134,6 @@ void __init tegra30_init_early(void)
>  	tegra_init_cache(0x441, 0x551);
>  	tegra_pmc_init();
>  	tegra_powergate_init();
> +	tegra_ahb_gizmo_init();
>  }
>  #endif

Does it really have to be "early", rather than an initcall? Why?

> +
> +static inline unsigned long gizmo_readl(unsigned long offset)
> +{
> +	return readl(IO_TO_VIRT(TEGRA_AHB_GIZMO_BASE + offset));
> +}
> +
> +static inline void gizmo_writel(unsigned long value, unsigned long offset)
> +{
> +	writel(value, IO_TO_VIRT(TEGRA_AHB_GIZMO_BASE + offset));
> +}

Please change this to no longer use hardcoded addresses. A good
implementation would scan the device tree for the physical address
and then ioremap the registers in the init function, in order to
save a local __iomem pointer.

	Arnd
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