[PATCH v5 2/3] pwm: add MediaTek display PWM driver support
Daniel Kurtz
djkurtz at chromium.org
Thu Jul 16 08:21:37 PDT 2015
On Thu, Jul 16, 2015 at 3:17 PM, YH Huang <yh.huang at mediatek.com> wrote:
> On Thu, 2015-07-16 at 14:54 +0800, Daniel Kurtz wrote:
>> On Thu, Jul 16, 2015 at 1:38 PM, YH Huang <yh.huang at mediatek.com> wrote:
>> > On Wed, 2015-07-15 at 23:59 +0800, YH Huang wrote:
>> >> On Mon, 2015-07-13 at 18:19 +0800, Daniel Kurtz wrote:
>> >> > On Mon, Jul 13, 2015 at 5:04 PM, YH Huang <yh.huang at mediatek.com> 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 at mediatek.com>
>> >> > > ---
>> >> > > drivers/pwm/Kconfig | 10 ++
>> >> > > drivers/pwm/Makefile | 1 +
>> >> > > drivers/pwm/pwm-mtk-disp.c | 256 +++++++++++++++++++++++++++++++++++++++++++++
>> >> > > 3 files changed, 267 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
>> >> > > + 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/Makefile b/drivers/pwm/Makefile
>> >> > > index ec50eb5..99c9e75 100644
>> >> > > --- a/drivers/pwm/Makefile
>> >> > > +++ b/drivers/pwm/Makefile
>> >> > > @@ -18,6 +18,7 @@ obj-$(CONFIG_PWM_LPC32XX) += pwm-lpc32xx.o
>> >> > > obj-$(CONFIG_PWM_LPSS) += pwm-lpss.o
>> >> > > obj-$(CONFIG_PWM_LPSS_PCI) += pwm-lpss-pci.o
>> >> > > obj-$(CONFIG_PWM_LPSS_PLATFORM) += pwm-lpss-platform.o
>> >> > > +obj-$(CONFIG_PWM_MTK_DISP) += pwm-mtk-disp.o
>> >> > > obj-$(CONFIG_PWM_MXS) += pwm-mxs.o
>> >> > > obj-$(CONFIG_PWM_PCA9685) += pwm-pca9685.o
>> >> > > obj-$(CONFIG_PWM_PUV3) += pwm-puv3.o
>> >> > > diff --git a/drivers/pwm/pwm-mtk-disp.c b/drivers/pwm/pwm-mtk-disp.c
>> >> > > new file mode 100644
>> >> > > index 0000000..1f17cee
>> >> > > --- /dev/null
>> >> > > +++ b/drivers/pwm/pwm-mtk-disp.c
>> >> > > @@ -0,0 +1,256 @@
>> >> > > +/*
>> >> > > + * MediaTek display pulse-width-modulation controller driver.
>> >> > > + * Copyright (c) 2015 MediaTek Inc.
>> >> > > + * Author: YH Huang <yh.huang at mediatek.com>
>> >> > > + *
>> >> > > + * 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>
>> >> > > +#include <linux/slab.h>
>> >> > > +
>> >> > > +#define DISP_PWM_EN 0
>> >> >
>> >> > The "DISP_PWM_*" are register offsets, so use a hex value, like this:
>> >> >
>> >> > #define DISP_PWM_EN 0x00
>> >> >
>> >> > Use BIT() for register *fields*, that is, the individual bits of a register.
>> >> >
>> >>
>> >> Got it!
>> >>
>> >> > > +#define PWM_ENABLE_MASK BIT(0)
>> >> > > +
>> >> > > +#define DISP_PWM_COMMIT BIT(3)
>> >> >
>> >> > #define DISP_PWM_COMMIT 0x08
>> >> >
>> >> > > +#define PWM_COMMIT_MASK BIT(0)
>> >> > > +
>> >> > > +#define DISP_PWM_CON_0 BIT(4)
>> >> >
>> >> > #define DISP_PWM_COMMIT 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
>> >> > > +
>> >> > > +#define PWM_HIGH_WIDTH_SHIFT 16
>> >> > > +#define PWM_HIGH_WIDTH_MASK (0x1fff << PWM_HIGH_WIDTH_SHIFT)
>> >> > > +
>> >> > > +struct mtk_disp_pwm {
>> >> > > + struct pwm_chip chip;
>> >> > > + struct device *dev;
>> >> >
>> >> > I don't think "dev" is actually used. And, if needed, it can be
>> >> > extracted from "chip".
>> >> >
>> >>
>> >> I will drop it.
>> >>
>> >> > > + struct clk *clk_main;
>> >> > > + struct clk *clk_mm;
>> >> > > + void __iomem *base;
>> >> > > +};
>> >> > > +
>> >> > > +static inline struct mtk_disp_pwm *to_mtk_disp_pwm(struct pwm_chip *chip)
>> >> > > +{
>> >> > > + return container_of(chip, struct mtk_disp_pwm, chip);
>> >> > > +}
>> >> > > +
>> >> > > +static void mtk_disp_pwm_update_bits(void __iomem *address, u32 mask, u32 value)
>> >> >
>> >> > Take "struct mtk_disp_pwm *mdp" as a param and extract mdp->base,
>> >> > rather than pass the raw iomem address.
>> >> >
>> >>
>> >> I will revise it like this.
>> >>
>> >> static void mtk_disp_pwm_update_bits(struct mtk_disp_pwm *mdp,
>> >> u32 reg, u32 mask, u32 value)
>> >> {
>> >> void __iomem *address;
>> >> u32 val;
>> >>
>> >> address = mdp->base + reg;
>> >> val = readl(address);
>> >> val &= ~mask;
>> >> val |= value;
>> >> writel(val, address);
>> >> }
>> >>
>> >> > > +{
>> >> > > + u32 val;
>> >> > > +
>> >> > > + val = readl(address);
>> >> > > + val &= ~mask;
>> >> > > + val |= value;
>> >> > > + writel(val, address);
>> >> > > +}
>> >> > > +
>> >> > > +static int mtk_disp_pwm_config(struct pwm_chip *chip, struct pwm_device *pwm,
>> >> > > + int duty_ns, int period_ns)
>> >> > > +{
>> >> > > + struct mtk_disp_pwm *mdp = to_mtk_disp_pwm(chip);
>> >> > > + u64 div, rate;
>> >> > > + u32 clk_div, period, high_width, value;
>> >> > > +
>> >> > > + /*
>> >> > > + * Find period, high_width and clk_div to suit duty_ns and period_ns.
>> >> > > + * Calculate proper div value to keep period value in the bound.
>> >> > > + *
>> >> > > + * period_ns = 10^9 * (clk_div + 1) * (period + 1) / PWM_CLK_RATE
>> >> > > + * duty_ns = 10^9 * (clk_div + 1) * high_width / PWM_CLK_RATE
>> >> > > + *
>> >> > > + * period = (PWM_CLK_RATE * period_ns) / (10^9 * (clk_div + 1)) - 1
>> >> > > + * high_width = (PWM_CLK_RATE * duty_ns) / (10^9 * (clk_div + 1))
>> >> > > + */
>> >> > > + rate = clk_get_rate(mdp->clk_main);
>> >> > > + clk_div = div_u64(rate * period_ns, NSEC_PER_SEC) >>
>> >> > > + PWM_PERIOD_BIT_SHIFT;
>> >> > > + if (clk_div > PWM_CLKDIV_MAX)
>> >> > > + return -EINVAL;
>> >> > > +
>> >> > > + div = NSEC_PER_SEC * (clk_div + 1);
>> >> > > + period = div64_u64(rate * period_ns, div);
>> >> > > + if (period > 0)
>> >> > > + period--;
>> >> > > +
>> >> > > + high_width = div64_u64(rate * duty_ns, div);
>> >> > > +
>> >> > > + mtk_disp_pwm_update_bits(mdp->base + DISP_PWM_CON_0,
>> >> > > + PWM_CLKDIV_MASK, clk_div << PWM_CLKDIV_SHIFT);
>> >> > > +
>> >> > > + value = period | (high_width << PWM_HIGH_WIDTH_SHIFT);
>> >> > > + mtk_disp_pwm_update_bits(mdp->base + DISP_PWM_CON_1,
>> >> > > + PWM_PERIOD_MASK | PWM_HIGH_WIDTH_MASK, value);
>> >> > > +
>> >> > > + mtk_disp_pwm_update_bits(mdp->base + DISP_PWM_COMMIT,
>> >> > > + PWM_COMMIT_MASK, 1);
>> >> > > + mtk_disp_pwm_update_bits(mdp->base + DISP_PWM_COMMIT,
>> >> > > + PWM_COMMIT_MASK, 0);
>> >> > > +
>> >> > > + return 0;
>> >> > > +}
>> >> > > +
>> >> > > +static int mtk_disp_pwm_enable(struct pwm_chip *chip, struct pwm_device *pwm)
>> >> > > +{
>> >> > > + struct mtk_disp_pwm *mdp = to_mtk_disp_pwm(chip);
>> >> > > +
>> >> > > + mtk_disp_pwm_update_bits(mdp->base + DISP_PWM_EN,
>> >> > > + PWM_ENABLE_MASK, 1);
>> >> > > +
>> >> > > + return 0;
>> >> > > +}
>> >> > > +
>> >> > > +static void mtk_disp_pwm_disable(struct pwm_chip *chip, struct pwm_device *pwm)
>> >> > > +{
>> >> > > + struct mtk_disp_pwm *mdp = to_mtk_disp_pwm(chip);
>> >> > > +
>> >> > > + mtk_disp_pwm_update_bits(mdp->base + DISP_PWM_EN,
>> >> > > + PWM_ENABLE_MASK, 0);
>> >> > > +}
>> >> > > +
>> >> > > +static const struct pwm_ops mtk_disp_pwm_ops = {
>> >> > > + .config = mtk_disp_pwm_config,
>> >> > > + .enable = mtk_disp_pwm_enable,
>> >> > > + .disable = mtk_disp_pwm_disable,
>> >> > > + .owner = THIS_MODULE,
>> >> > > +};
>> >> > > +
>> >> > > +static int mtk_disp_pwm_probe(struct platform_device *pdev)
>> >> > > +{
>> >> > > + struct mtk_disp_pwm *mdp;
>> >> > > + struct resource *r;
>> >> > > + int ret;
>> >> > > +
>> >> > > + mdp = devm_kzalloc(&pdev->dev, sizeof(*mdp), GFP_KERNEL);
>> >> > > + if (!mdp)
>> >> > > + return -ENOMEM;
>> >> > > +
>> >> > > + mdp->dev = &pdev->dev;
>> >> > > +
>> >> > > + r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> >> > > + mdp->base = devm_ioremap_resource(&pdev->dev, r);
>> >> > > + if (IS_ERR(mdp->base))
>> >> > > + return PTR_ERR(mdp->base);
>> >> > > +
>> >> > > + mdp->clk_main = devm_clk_get(&pdev->dev, "main");
>> >> > > + if (IS_ERR(mdp->clk_main))
>> >> > > + return PTR_ERR(mdp->clk_main);
>> >> > > +
>> >> > > + mdp->clk_mm = devm_clk_get(&pdev->dev, "mm");
>> >> > > + if (IS_ERR(mdp->clk_mm))
>> >> > > + return PTR_ERR(mdp->clk_mm);
>> >> > > +
>> >> > > + ret = clk_prepare_enable(mdp->clk_main);
>> >> >
>> >> > Delay turning on the PWM clock until it is actually needed (pwm_enable)...
>> >> > Just be careful to ensure that the "main" clock is enabled when
>> >> > writing registers during mtk_disp_pwm_config.
>> >
>> > Since pwm-backlight driver configures PWM before enable PWM, I enable
>> > clocks at the probe function.
>> > Turning on the PWM clock in pwm_enable will lose the first configuration
>> > of PWM. It won't affect a lot since the system configures PWM many times
>> > at boot time.
>> > So should I delay or keep the original way?
>>
>> Why does turning on the PWM clock in pwm_enable lose the first configuration?
>> Would this be solved by turning enabling/disabling clocks during
>> mtk_disp_pwm_config()?
>>
>
> If I don't enable clocks at probe function, I enable clocks at
> mtk_disp_pwm_enable() and disable clocks at mtk_disp_pwm_disable().
> And this causes missing first configuration.
>
> Enabling clocks in mtk_disp_pwm_config() will fix this.
> The backlight doesn't work well(no immediate update or losing backlight)
> if I disable anyone of the two clocks in mtk_disp_pwm_config().
>
> Regards,
> YH Huang
>
>> >
>> >> > By the way, is the pwm in a power domain that must also be enabled
>> >> > when enabling the pwm?
>> >>
>> >> It is in the display power domain which must also be enabled.
>> >>
>> >> >
>> >> > > + if (ret < 0)
>> >> > > + return ret;
>> >> > > +
>> >> > > + ret = clk_prepare_enable(mdp->clk_mm);
>> >> > > + if (ret < 0)
>> >> > > + goto disable_clk_main;
>> >> > > +
>> >> > > + platform_set_drvdata(pdev, mdp);
>> >> >
>> >> > Set this only after pwmchip_add() succeeds.
>> >>
>> >> OK.
>> >>
>> >> >
>> >> > > +
>> >> > > + mdp->chip.dev = &pdev->dev;
>> >> > > + mdp->chip.ops = &mtk_disp_pwm_ops;
>> >> > > + mdp->chip.base = -1;
>> >> > > + mdp->chip.npwm = 1;
>> >> > > +
>> >> > > + ret = pwmchip_add(&mdp->chip);
>> >> > > + if (ret < 0) {
>> >> > > + dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
>> >> > > + goto disable_clk_mm;
>> >> > > + }
>> >> > > +
>> >> > > + return 0;
>> >> > > +
>> >> > > +disable_clk_mm:
>> >> > > + clk_disable_unprepare(mdp->clk_mm);
>> >> > > +disable_clk_main:
>> >> > > + clk_disable_unprepare(mdp->clk_main);
>> >> > > + return ret;
>> >> > > +}
>> >> > > +
>> >> > > +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);
>> >> > > +
>> >> > > + clk_disable_unprepare(mdp->clk_main);
>> >> > > + clk_disable_unprepare(mdp->clk_mm);
>> >> >
>> >> > Nit: it is more traditional to disable clocks in the opposite order to
>> >> > which they are enabled, so:
>> >> >
>> >> > clk_disable_unprepare(mdp->clk_mm);
>> >> > clk_disable_unprepare(mdp->clk_main);
>> >> >
>> >>
>> >> OK.
>> >>
>> >> > > +
>> >> > > + return ret;
>> >> > > +}
>> >> > > +
>> >> > > +static const struct of_device_id mtk_disp_pwm_of_match[] = {
>> >> > > + { .compatible = "mediatek,mt8173-disp-pwm" },
>> >> > > + { .compatible = "mediatek,mt6595-disp-pwm" },
>> >> > > + { }
>> >> > > +};
>> >> > > +MODULE_DEVICE_TABLE(of, mtk_disp_pwm_of_match);
>> >> > > +
>> >> > > +#ifdef CONFIG_PM_SLEEP
>> >> > > +static int mtk_disp_pwm_suspend(struct device *dev)
>> >> > > +{
>> >> > > + struct mtk_disp_pwm *mdp = dev_get_drvdata(dev);
>> >> > > +
>> >> > > + clk_disable_unprepare(mdp->clk_main);
>> >> > > + clk_disable_unprepare(mdp->clk_mm);
>> >> > > +
>> >> > > + return 0;
>> >> > > +}
>> >> > > +
>> >> > > +static int mtk_disp_pwm_resume(struct device *dev)
>> >> > > +{
>> >> > > + struct mtk_disp_pwm *mdp = dev_get_drvdata(dev);
>> >> > > + int ret;
>> >> > > +
>> >> > > + ret = clk_prepare_enable(mdp->clk_main);
>> >> > > + if (ret < 0)
>> >> > > + return ret;
>> >> > > +
>> >> > > + ret = clk_prepare_enable(mdp->clk_mm);
>> >> > > + if (ret < 0) {
>> >> > > + clk_disable_unprepare(mdp->clk_main);
>> >> > > + return ret;
>> >> > > + }
>> >> > > +
>> >> >
>> >> > Don't you also have to restore the PWM rate and frequency?
>> >> >
>> >> > Is it possible to save power at runtime by leaving mdp->clk_mm enabled
>> >> > (to generate the PWM signal), but disable mdp->clk_main (clock
>> >> > required to access PWM registers)?
>> >>
>> >> The pwm-backlight driver will restore the data.
>> >>
>> >> After I try to disable anyone of the two clocks at runtime, the
>> >> backlight doesn't work well(no immediate update or losing backlight).
>> >> So we need to keep both clock enabled.
Do you mean you see backlight glitch because the clocks / backlight
were *already on* during the first config (Perhaps left on by the
bootloader)?
I don't know how to solve that problem.
Maybe Thierry does.
In any case, this is a minor issue; we really shouldn't hold up
landing the driver to optimize when the clocks are enabled/disabled
:-). I'm happy enough with what you have in this patch.
-Dan
>> >>
>> >> Regards,
>> >> YH Huang
>> >>
>> >
>> >
>
>
More information about the linux-arm-kernel
mailing list