linux-kernel - Re: [PATCH 1/4] ARM: rockchip: rk3288: Switch to use the proper PWM IP

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Message-ID: <20140819071011.GC12859@ulmo>
Date:	Tue, 19 Aug 2014 09:10:12 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Doug Anderson <dianders@...omium.org>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Caesar Wang <caesar.wang@...k-chips.com>,
	Sonny Rao <sonnyrao@...omium.org>, olof@...om.net,
	Eddie Cai <eddie.cai@...k-chips.com>, linux@....linux.org.uk,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] ARM: rockchip: rk3288: Switch to use the proper PWM
 IP

On Mon, Aug 18, 2014 at 10:09:06AM -0700, Doug Anderson wrote:
> The rk3288 SoC has an option to switch all of the PWMs in the system
> between the old IP block and the new IP block.  The new IP block is
> working and tested and the suggested PWM to use, so setup the SoC to
> use it and then we can pretend that the other IP block doesn't exist.
> 
> This code could go lots of other places, but we've put it here.  Why?
> - Pushing it to the bootloader just makes the code harder to update in
>   the field.  If we later find a bug in the new IP block and want to
>   change our mind about what to use we want it to be easy to update.
> - Putting this code in the driver for IP block is a lot of extra work,
>   device tree bindings, etc.  Now that the new IP block is validated
>   it's likely no future SoCs will need this code.  Why pollute the PWM
>   driver with this?  This is an rk3288 thing so it should be in rk3288
>   code.
> - There's a single bit that switches over PWMs, which makes it extra
>   hard to put this under the PWM device tree nodes.
> 
> Signed-off-by: Doug Anderson <dianders@...omium.org>
> ---
>  arch/arm/mach-rockchip/rockchip.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
> 
> diff --git a/arch/arm/mach-rockchip/rockchip.c b/arch/arm/mach-rockchip/rockchip.c
> index 8ab9e0e..99133b9 100644
> --- a/arch/arm/mach-rockchip/rockchip.c
> +++ b/arch/arm/mach-rockchip/rockchip.c
> @@ -24,6 +24,24 @@
>  #include <asm/hardware/cache-l2x0.h>
>  #include "core.h"
>  
> +static void __init rk3288_init_machine(void)
> +{
> +	void *grf = ioremap(0xff770000, 0x10000);

This region of memory is part of the "grf" "syscon" device (according to
arch/arm/boot/dts/rk3288.dtsi) so the register should be accessed from
that driver. It looks as if no such driver currently exists, but given
the existence of the device tree node it's fair to assume that one will
eventually be merged.

Thierry

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