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

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Date:	Mon, 18 Aug 2014 10:19:51 -0700
From:	Doug Anderson <dianders@...omium.org>
To:	Sonny Rao <sonnyrao@...omium.org>
Cc:	Heiko Stuebner <heiko@...ech.de>,
	Thierry Reding <thierry.reding@...il.com>,
	Caesar Wang <caesar.wang@...k-chips.com>,
	Olof Johansson <olof@...om.net>,
	Eddie Cai <eddie.cai@...k-chips.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/4] ARM: rockchip: rk3288: Switch to use the proper PWM IP

Sonny,

On Mon, Aug 18, 2014 at 10:11 AM, Sonny Rao <sonnyrao@...omium.org> wrote:
> On Mon, Aug 18, 2014 at 10:09 AM, Doug Anderson <dianders@...omium.org> 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);
>
> Is it worth checking for failure here?  Will the system boot without this?

Yes, the system will boot without it.  I can't quite imagine the
ioremap failing, but I can add a test.

-Doug
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