[rfc]pwm: add BCM2835 PWM driver

[Bart Tanghe]

Is it the responsibility of the pwm driver to handle the pinmux of the 
io pins? Or is the end user, or a parent driver responsible to handle this?
Idem for the clock?


On 04/09/2014 05:59 PM, Tim Kryger wrote:
> On Tue, Apr 8, 2014 at 6:27 PM, Stephen Warren <swarren at wwwdotorg.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 at thomasmore.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.