Re: [PATCH] ARM: EXYNOS4: Add PWM backlight support on Samsung SMDKV310

[JinGoo Han <jg1.han@samsung.com>]

Hi, Banajit.
> -----Original Message-----
> From: linux-samsung-soc-owner@vger.kernel.org [mailto:linux-samsung-soc-
> owner@vger.kernel.org] On Behalf Of Banajit Goswami
> Sent: Wednesday, June 22, 2011 3:41 PM
> To: linux-samsung-soc@vger.kernel.org
> Cc: kgene.kim@samsung.com; ben-linux@fluff.org; linux-arm-
> kernel@lists.infradead.org; Banajit Goswami
> Subject: [PATCH] ARM: EXYNOS4: Add PWM backlight support on Samsung
> SMDKV310
> 
> This patch adds support for LCD backlight using PWM timer for
> Samsung SMDKV310 board.
> 
> Signed-off-by: Banajit Goswami <banajit.g@samsung.com>
> ---
>  arch/arm/mach-exynos4/Kconfig         |    1 +
>  arch/arm/mach-exynos4/mach-smdkv310.c |   43
> +++++++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+), 0 deletions(-)
> 
> diff --git a/arch/arm/mach-exynos4/Kconfig b/arch/arm/mach-exynos4/Kconfig
> index 1435fc3..9ab53bc 100644
> --- a/arch/arm/mach-exynos4/Kconfig
> +++ b/arch/arm/mach-exynos4/Kconfig
> @@ -128,6 +128,7 @@ config MACH_SMDKV310
>  	select S3C_DEV_HSMMC2
>  	select S3C_DEV_HSMMC3
>  	select SAMSUNG_DEV_KEYPAD
> +	select SAMSUNG_DEV_PWM
>  	select EXYNOS4_DEV_PD
>  	select EXYNOS4_DEV_SYSMMU
>  	select EXYNOS4_SETUP_I2C1
> diff --git a/arch/arm/mach-exynos4/mach-smdkv310.c b/arch/arm/mach-
> exynos4/mach-smdkv310.c
> index 7e3ee6c..b097ef6 100644
> --- a/arch/arm/mach-exynos4/mach-smdkv310.c
> +++ b/arch/arm/mach-exynos4/mach-smdkv310.c
> @@ -16,6 +16,7 @@
>  #include <linux/io.h>
>  #include <linux/i2c.h>
>  #include <linux/input.h>
> +#include <linux/pwm_backlight.h>
> 
>  #include <asm/mach/arch.h>
>  #include <asm/mach-types.h>
> @@ -29,6 +30,7 @@
>  #include <plat/sdhci.h>
>  #include <plat/iic.h>
>  #include <plat/pd.h>
> +#include <plat/gpio-cfg.h>
> 
>  #include <mach/map.h>
> 
> @@ -172,6 +174,45 @@ static struct i2c_board_info i2c_devs1[] __initdata =
> {
>  	{I2C_BOARD_INFO("wm8994", 0x1a),},
>  };
> 
> +static int smdkv310_backlight_init(struct device *dev)
> +{
> +	int ret = 0;
> +
> +	ret = gpio_request(EXYNOS4_GPD0(1), "Backlight");
> +	if (ret) {
> +		printk(KERN_ERR "failed to request GPD for PWM-OUT0\n");
> +		return ret;
> +	}
> +
> +	/* Configure GPIO pin with EXYNOS4_GPD_0_1_TOUT_0 */
> +	s3c_gpio_cfgpin(EXYNOS4_GPD0(1), S3C_GPIO_SFN(2));
> +
> +	return 0;
> +}
> +
> +static void smdkv310_backlight_exit(struct device *dev)
> +{
> +	s3c_gpio_cfgpin(EXYNOS4_GPD0(1), S3C_GPIO_OUTPUT);
> +	gpio_free(EXYNOS4_GPD0(1));
> +}
> +
> +static struct platform_pwm_backlight_data smdkv310_backlight_data = {
> +	.pwm_id		= 1,
> +	.max_brightness	= 255,
> +	.dft_brightness	= 255,
> +	.pwm_period_ns	= 78770,
Please use 1000 as pwm_period_ns instead of 78770 as follows:
-	.pwm_period_ns	= 78770,
+	.pwm_period_ns  = 1000,

The value '78770' makes noise related to resonance at LCD board.

I will explain how I get the value of PWM period.

The SMDK boards use LT3591 as backlight LED driver of LTE480WV LCD
According to the LT3591 datasheet, the switching frequency should
be 1MHz. So, PWM period is calculated by following formula:
        PWM period = 1/switching frequency
                       = 1/1MHz
                       = 1000 ns

You can find LT3591 datasheet easily on the Internet. Please refer to it
for more information.
Good luck.
> +	.init		= smdkv310_backlight_init,
> +	.exit		= smdkv310_backlight_exit,
> +};
> +
> +static struct platform_device smdkv310_backlight_device = {
> +	.name		= "pwm-backlight",
> +	.dev		= {
> +		.parent		= &s3c_device_timer[1].dev,
> +		.platform_data	= &smdkv310_backlight_data,
> +	},
> +};
> +
>  static struct platform_device *smdkv310_devices[] __initdata = {
>  	&s3c_device_hsmmc0,
>  	&s3c_device_hsmmc1,
> @@ -195,6 +236,8 @@ static struct platform_device *smdkv310_devices[]
> __initdata = {
>  	&samsung_asoc_dma,
>  	&smdkv310_smsc911x,
>  	&smdkv310_pcm_device,
> +	&s3c_device_timer[1],
> +	&smdkv310_backlight_device,
>  };
> 
>  static void __init smdkv310_smsc911x_init(void)
> --
> 1.6.5.2
> 
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