Re: [PATCH v6 2/3] pwm: add MediaTek display PWM driver support

[YH Huang]

On Mon, 2015-08-17 at 15:23 +0200, Thierry Reding wrote:
> On Mon, Jul 20, 2015 at 04:17:16PM +0800, YH Huang wrote:
> > Add display PWM driver support to modify backlight for MT8173 and MT6595.
> > The PWM has one channel to control the brightness of the display.
> > When the (high_width / period) is closer to 1, the screen is brighter;
> > otherwise, it is darker.
> > 
> > Signed-off-by: YH Huang <yh.huang@xxxxxxxxxxxx>
> > ---
> >  drivers/pwm/Kconfig        |  10 ++
> >  drivers/pwm/Makefile       |   1 +
> >  drivers/pwm/pwm-mtk-disp.c | 232 +++++++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 243 insertions(+)
> >  create mode 100644 drivers/pwm/pwm-mtk-disp.c
> > 
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index b1541f4..f5b03a4 100644
> > --- a/drivers/pwm/Kconfig
> > +++ b/drivers/pwm/Kconfig
> > @@ -211,6 +211,16 @@ config PWM_LPSS_PLATFORM
> >  	  To compile this driver as a module, choose M here: the module
> >  	  will be called pwm-lpss-platform.
> >  
> > +config PWM_MTK_DISP
> > +	tristate "MediaTek display PWM driver"
> > +	depends on ARCH_MEDIATEK || COMPILE_TEST
> 
> This is going to break randconfig builds. From a quick look your driver
> will fail to build at least on architectures that don't set HAVE_IOMEM.
> I know that's quite exotic, but I've had to deal with fallout from
> things like this in the past. If you want || COMPILE_TEST you should at
> least add a "depends on HAVE_IOMEM".
> 
> linux/clk.h seems to have stubs for all of the functions that you use,
> so those shouldn't be a problem.
> 

I will add it and this will be like:

depends on ARCH_MEDIATEK || COMPILE_TEST
depends on HAS_IOMEM

> > +	help
> > +	  Generic PWM framework driver for MediaTek disp-pwm device.
> > +	  The PWM is used to control the backlight brightness for display.
> > +
> > +	  To compile this driver as a module, choose M here: the module
> > +	  will be called pwm-mtk-disp.
> > +
> >  config PWM_MXS
> >  	tristate "Freescale MXS PWM support"
> >  	depends on ARCH_MXS && OF
> [...]
> > diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c
> > new file mode 100644
> > index 0000000..69682a0
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-mtk-disp.c
> > @@ -0,0 +1,232 @@
> > +/*
> > + * MediaTek display pulse-width-modulation controller driver.
> > + * Copyright (c) 2015 MediaTek Inc.
> > + * Author: YH Huang <yh.huang@xxxxxxxxxxxx>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + *
> > + * This program is distributed in the hope that it will be useful,
> > + * but WITHOUT ANY WARRANTY; without even the implied warranty of
> > + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> > + * GNU General Public License for more details.
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/pwm.h>
> > +#include <linux/platform_device.h>
> 
> The above two aren't correctly sorted.
> 

Arrange like this:

#include <linux/platform_device.h>
#include <linux/pwm.h>

> > +#include <linux/slab.h>
> > +
> > +#define DISP_PWM_EN		0x00
> > +#define PWM_ENABLE_MASK		BIT(0)
> > +
> > +#define DISP_PWM_COMMIT		0x08
> > +#define PWM_COMMIT_MASK		BIT(0)
> > +
> > +#define DISP_PWM_CON_0		0x10
> > +#define PWM_CLKDIV_SHIFT	16
> > +#define PWM_CLKDIV_MAX		0x3ff
> > +#define PWM_CLKDIV_MASK		(PWM_CLKDIV_MAX << PWM_CLKDIV_SHIFT)
> > +
> > +#define DISP_PWM_CON_1		0x14
> > +#define PWM_PERIOD_MASK		0xfff
> > +/* Shift log2(PWM_PERIOD_MASK + 1) as divisor */
> > +#define PWM_PERIOD_BIT_SHIFT	12
> 
> There are still two names for the same value here. I thought we had
> agreed on this becoming something like the below?
> 
> 	#define PWM_PERIOD_BIT_SHIFT 12
> 	#define PWM_PERIOD_MASK ((1 << PWM_PERIOD_BIT_SHIFT) - 1)
> 
> Although PWM_PERIOD_BIT_WIDTH would probably be a better name. Or
> PWM_PERIOD_BITS or similar.
> 

I will revise to 

#define PWM_PERIOD_BIT_WIDTH 12
#define PWM_PERIOD_MASK ((1 << PWM_PERIOD_BIT_WIDTH) - 1)

> > +static int mtk_disp_pwm_remove(struct platform_device *pdev)
> > +{
> > +	struct mtk_disp_pwm *mdp = platform_get_drvdata(pdev);
> > +	int ret = pwmchip_remove(&mdp->chip);
> 
> I'd prefer this to be separate lines:
> 
> 	int ret;
> 
> 	ret = pwmchip_remove(&mdp->chip);

OK.

Thanks for your suggestions.

Regards,
YH Huang


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