Re: [PATCH RESEND 2/3] pwm: kona: Add support for Broadcom iproc pwm controller

[Boris Brezillon <boris.brezillon@free-electrons.com>]

Hi,

On Tue, 10 May 2016 16:40:24 +0200
Thierry Reding <thierry.reding@gmail.com> wrote:

> On Tue, Mar 29, 2016 at 10:22:29AM -0400, Yendapally Reddy Dhananjaya Reddy wrote:
> > Update the kona driver to support Broadcom iproc pwm controller
> > 
> > Signed-off-by: Yendapally Reddy Dhananjaya Reddy <yendapally.reddy@broadcom.com>
> > ---
> >  drivers/pwm/Kconfig        |   6 +-
> >  drivers/pwm/pwm-bcm-kona.c | 183 +++++++++++++++++++++++++++++++++++++++------
> >  2 files changed, 163 insertions(+), 26 deletions(-)
> > 
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index c182efc..e45ea33 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -76,9 +76,11 @@ config PWM_ATMEL_TCB
> >  
> >  config PWM_BCM_KONA
> >  	tristate "Kona PWM support"
> > -	depends on ARCH_BCM_MOBILE
> > +	depends on ARCH_BCM_MOBILE || ARCH_BCM_IPROC
> > +	default ARCH_BCM_IPROC  
> 
> Why the default? Typically you'd enable this in one or more of the
> default configurations. default ARCH_* is really only useful if the
> driver is essential. PWM doesn't usually fall into this category.
> 
> > diff --git a/drivers/pwm/pwm-bcm-kona.c b/drivers/pwm/pwm-bcm-kona.c
> > index c634183..ef152e3a 100644
> > --- a/drivers/pwm/pwm-bcm-kona.c
> > +++ b/drivers/pwm/pwm-bcm-kona.c
> > @@ -19,6 +19,7 @@
> >  #include <linux/math64.h>
> >  #include <linux/module.h>
> >  #include <linux/of.h>
> > +#include <linux/of_device.h>
> >  #include <linux/platform_device.h>
> >  #include <linux/pwm.h>
> >  #include <linux/slab.h>
> > @@ -47,30 +48,90 @@
> >  
> >  #define PWM_CONTROL_OFFSET			(0x00000000)
> >  #define PWM_CONTROL_SMOOTH_SHIFT(chan)		(24 + (chan))
> > -#define PWM_CONTROL_TYPE_SHIFT(chan)		(16 + (chan))
> > +#define PWM_CONTROL_TYPE_SHIFT(shift, chan)	(shift + chan)  
> 
> You need to put the parameters into parentheses to avoid expansion from
> potentially messing up the expression.
> 
> >  #define PWM_CONTROL_POLARITY_SHIFT(chan)	(8 + (chan))
> >  #define PWM_CONTROL_TRIGGER_SHIFT(chan)		(chan)
> >  
> >  #define PRESCALE_OFFSET				(0x00000004)
> > -#define PRESCALE_SHIFT(chan)			((chan) << 2)
> > -#define PRESCALE_MASK(chan)			(0x7 << PRESCALE_SHIFT(chan))
> > +#define PRESCALE_SHIFT				(0x00000004)
> > +#define PRESCALE_MASK				(0x00000007)  
> 
> Hmm... this looks odd. Why are you dropping the chan parameter here?
> 
> >  #define PRESCALE_MIN				(0x00000000)
> >  #define PRESCALE_MAX				(0x00000007)
> >  
> > -#define PERIOD_COUNT_OFFSET(chan)		(0x00000008 + ((chan) << 3))
> > +#define PERIOD_COUNT_OFFSET(offset, chan)	(offset + (chan << 3))  
> 
> Need parentheses here as well.
> 
> >  #define PERIOD_COUNT_MIN			(0x00000002)
> >  #define PERIOD_COUNT_MAX			(0x00ffffff)
> > +#define KONA_PERIOD_COUNT_OFFSET		(0x00000008)
> >  
> > -#define DUTY_CYCLE_HIGH_OFFSET(chan)		(0x0000000c + ((chan) << 3))
> > +#define DUTY_CYCLE_HIGH_OFFSET(offset, chan)	(offset + (chan << 3))
> >  #define DUTY_CYCLE_HIGH_MIN			(0x00000000)
> >  #define DUTY_CYCLE_HIGH_MAX			(0x00ffffff)
> > +#define KONA_DUTY_CYCLE_HIGH_OFFSET		(0x0000000c)
> > +
> > +#define PWM_CHANNEL_CNT				(0x00000006)
> > +#define SIGNAL_PUSH_PULL			(0x00000001)
> > +#define PWMOUT_TYPE_SHIFT			(0x00000010)
> > +
> > +#define IPROC_PRESCALE_OFFSET			(0x00000024)
> > +#define IPROC_PRESCALE_SHIFT			(0x00000006)
> > +#define IPROC_PRESCALE_MAX			(0x0000003f)
> > +
> > +#define IPROC_PERIOD_COUNT_OFFSET		(0x00000004)
> > +#define IPROC_PERIOD_COUNT_MIN			(0x00000002)
> > +#define IPROC_PERIOD_COUNT_MAX			(0x0000ffff)
> > +
> > +#define IPROC_DUTY_CYCLE_HIGH_OFFSET		(0x00000008)
> > +#define IPROC_DUTY_CYCLE_HIGH_MIN		(0x00000000)
> > +#define IPROC_DUTY_CYCLE_HIGH_MAX		(0x0000ffff)
> > +
> > +#define IPROC_PWM_CHANNEL_CNT			(0x00000004)
> > +#define IPROC_SIGNAL_PUSH_PULL			(0x00000000)
> > +#define IPROC_PWMOUT_TYPE_SHIFT			(0x0000000f)
> > +
> > +/*
> > + * pwm controller reg structure
> > + *
> > + * @prescale_offset: prescale register offset
> > + * @period_offset: period register offset
> > + * @duty_offset: duty register offset
> > + * @no_of_channels: number of channels
> > + * @out_type_shift: out type shift in the register
> > + * @signal_type: push-pull or open drain
> > + * @prescale_max: prescale max
> > + * @prescale_shift: prescale shift in register
> > + * @prescale_ch_ascending: prescale ch order in prescale register
> > + * @duty_cycle_max: value of max duty cycle
> > + * @duty_cycle_min: value of min duty cycle
> > + * @period_count_max: max period count val
> > + * @period_count_min: min period count val
> > + * @smooth_output_support: pwm smooth output support
> > + */
> > +struct kona_pwmc_reg {
> > +	u32 prescale_offset;
> > +	u32 period_offset;
> > +	u32 duty_offset;
> > +	u32 no_of_channels;
> > +	u32 out_type_shift;
> > +	u32 signal_type;
> > +	u32 prescale_max;
> > +	u32 prescale_shift;
> > +	bool prescale_ch_ascending;
> > +	u32 duty_cycle_max;
> > +	u32 duty_cycle_min;
> > +	u32 period_count_max;
> > +	u32 period_count_min;
> > +	bool smooth_output_support;
> > +};  
> 
> This is rather tedious. It looks to me like this isn't very similar to
> the existing driver. Register offsets move around, bitfield positions
> change, feature set is different. Might be better off turning this into
> a separate driver after all.
> 
> > +static const struct kona_pwmc_reg kona_pwmc_reg_data = {
> > +	.prescale_offset = PRESCALE_OFFSET,
> > +	.period_offset = KONA_PERIOD_COUNT_OFFSET,
> > +	.duty_offset = KONA_DUTY_CYCLE_HIGH_OFFSET,
> > +	.no_of_channels = PWM_CHANNEL_CNT,
> > +	.out_type_shift = PWMOUT_TYPE_SHIFT,
> > +	.signal_type = SIGNAL_PUSH_PULL,
> > +	.prescale_max = PRESCALE_MAX,
> > +	.prescale_shift = PRESCALE_SHIFT,
> > +	.prescale_ch_ascending = false,
> > +	.duty_cycle_max = DUTY_CYCLE_HIGH_MAX,
> > +	.duty_cycle_min = DUTY_CYCLE_HIGH_MIN,
> > +	.period_count_max = PERIOD_COUNT_MAX,
> > +	.period_count_min = PERIOD_COUNT_MIN,
> > +	.smooth_output_support = true,
> > +};
> > +
> > +static const struct kona_pwmc_reg iproc_pwmc_reg_data = {
> > +	.prescale_offset = IPROC_PRESCALE_OFFSET,
> > +	.period_offset = IPROC_PERIOD_COUNT_OFFSET,
> > +	.duty_offset = IPROC_DUTY_CYCLE_HIGH_OFFSET,
> > +	.no_of_channels = IPROC_PWM_CHANNEL_CNT,
> > +	.out_type_shift = IPROC_PWMOUT_TYPE_SHIFT,
> > +	.signal_type = IPROC_SIGNAL_PUSH_PULL,
> > +	.prescale_max = IPROC_PRESCALE_MAX,
> > +	.prescale_shift = IPROC_PRESCALE_SHIFT,
> > +	.prescale_ch_ascending = true,
> > +	.duty_cycle_max = IPROC_DUTY_CYCLE_HIGH_MAX,
> > +	.duty_cycle_min = IPROC_DUTY_CYCLE_HIGH_MIN,
> > +	.period_count_max = IPROC_PERIOD_COUNT_MAX,
> > +	.period_count_min = IPROC_PERIOD_COUNT_MIN,
> > +	.smooth_output_support = false,
> > +};  
> 
> This looks like you could possible support a lot more hardware with this
> driver because it's now almost completely parameterized.
> 
> I don't see much sense in keeping this in the same driver and I think
> it'd be better to write a new one from scratch, even if that means
> slight duplication.
> 
> Or you'll have to make a very compelling argument as to why this is the
> better option.

Sorry to enter the discussion just now (Brian CCed me in an answer he
made to v4 of this series).

Honestly, I'd have the exact opposite argument: if you have a look at
newer versions of this patch, you'll see that more than 90% of the code
is duplicated, and re-using the same logic with different field
positions is quite common in other drivers. Actually the counter
argument to your suggestion are bug fixes: when you find a bug, you'll
have to remember fixing it for all implementations. Having a common
code base has IMO more pros than cons.

BTW, if you switch to regmap, you have this field-position
customization for free (see reg_field).

Regards,

Boris