linux-kernel - Re: [rfc]pwm: add BCM2835 PWM driver

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Date:	Wed, 9 Apr 2014 08:59:21 -0700
From:	Tim Kryger <tim.kryger@...aro.org>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Bart Tanghe <bart.tanghe@...masmore.be>,
	Thierry Reding <thierry.reding@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Linux PWM List <linux-pwm@...r.kernel.org>,
	linux-rpi-kernel@...ts.infradead.org
Subject: Re: [rfc]pwm: add BCM2835 PWM driver

On Tue, Apr 8, 2014 at 6:27 PM, Stephen Warren <swarren@...dotorg.org> wrote:
> On 04/08/2014 05:02 PM, Tim Kryger wrote:
>> On Thu, Apr 3, 2014 at 6:44 AM, Bart Tanghe <bart.tanghe@...masmore.be> wrote:
>>> need some recommendation
>>> the memory mapped io registers of the bcm2835 pwm hardware are spreaded
>>> over the memory mapped io
>>> gpio config 0x20200004 - clk config 0x201010A0 - pwm configuration 0x2020C000
>>> to handle this, I've used the base address of the memory mapped io
>>> so I can use positive offsets
>>
>> So the registers for this PWM are located in three distinct memory regions?
> ...
>>> +struct bcm2835_pwm_chip {
>>> +       struct pwm_chip chip;
>>> +       struct device *dev;
>>> +       int channel;
>>> +       void __iomem *mmio;
>>
>> One pointer isn't going to be enough.  You need three.
>>
>> I suggest renaming the first and adding two more:
>>
>> void __iomem *base_pwm;
>> void __iomem *base_clk;
>> void __iomem *base_alt;
>
> Sorry, I forgot about this patch. One comment here; the PWM driver can't
> touch the clock or alt registers; those should be owned by the clock
> driver, and the driver for whatever alt is (pinmux - don't recall what
> it's touching there).

Absolutely.  If these registers are owned by other drivers, go through them.
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