Re: [PATCH v2 2/2] pwm: add MediaTek display PWM driver support
From: YH Huang
Date: Thu Jun 18 2015 - 06:23:51 EST
On Fri, 2015-06-12 at 12:20 +0200, Thierry Reding wrote:
> On Thu, May 21, 2015 at 09:29:24PM +0800, YH Huang wrote:
> > Add display PWM driver support to modify backlight for MT8173.
> >
> > Signed-off-by: YH Huang <yh.huang@xxxxxxxxxxxx>
> > ---
> > drivers/pwm/Kconfig | 10 ++
> > drivers/pwm/Makefile | 1 +
> > drivers/pwm/pwm-mtk-disp.c | 228 +++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 239 insertions(+)
> > create mode 100644 drivers/pwm/pwm-mtk-disp.c
> >
> > diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> > index b1541f4..90e3c079 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 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/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..d4e4cb6
> > --- /dev/null
> > +++ b/drivers/pwm/pwm-mtk-disp.c
> > @@ -0,0 +1,228 @@
> > +/*
> > + * 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>
> > +#include <linux/slab.h>
> > +
> > +#define DISP_PWM_EN 0x0
> > +#define PWM_ENABLE_MASK 0x1
> > +
> > +#define DISP_PWM_COMMIT 0x08
> > +#define PWM_COMMIT_MASK 0x1
> > +
> > +#define DISP_PWM_CON_0 0x10
> > +#define PWM_CLKDIV_SHIFT 16
> > +#define PWM_CLKDIV_MASK (0x3ff << PWM_CLKDIV_SHIFT)
> > +#define PWM_CLKDIV_MAX 0x000003ff
>
> I think you should make this:
>
> #define PWM_CLKDIV_MAX 0x3ff
> #define PWM_CLKDIV_MASK (PWM_CLKDIV_MAX << PWM_CLKDIV_SHIFT)
>
> Just to show that these belong together.
>
It is much clear.
> > +
> > +#define DISP_PWM_CON_1 0x14
> > +#define PWM_PERIOD_MASK 0xfff
> > +#define PWM_PERIOD_MAX 0x00000fff
>
> Same here. PWM_PERIOD_MAX isn't actually used anywhere, so perhaps just
> drop it altogether. But see also below...
>
> > +/* Shift log2(PWM_PERIOD_MAX + 1) as divisor */
> > +#define PWM_PERIOD_BIT_SHIFT 12
>
> I wasn't very clear about this in my earlier review, so let me try to
> explain why I think this is confusing. You use this as a divisor, but
> you encode it as a shift. It's also PWM_PERIOD_MAX + 1, so I think it
> would make more sense to drop this, keep PWM_PERIOD_MAX as above and
> then replace the
>
> >> PWM_PERIOD_BIT_SHIFT
>
> below by
>
> / (PWM_PERIOD_MAX + 1)
>
Maybe I can change in this way:
Remove this: #define PWM_PERIOD_MAX 0x00000fff
Using ">> PWM_PERIOD_BIT_SHIFT" is faster than "/ (PWM_PERIOD_MAX + 1)"
Is this right?
> > +#define PWM_HIGH_WIDTH_SHIFT 16
> > +#define PWM_HIGH_WIDTH_MASK (0x1fff << PWM_HIGH_WIDTH_SHIFT)
>
> Why is the mask wider than for the period? That would imply that the
> duty cycle can be longer than a period, which doesn't make any sense.
> Can you clarify?
>
After discussing with the hardware designer, the duty cycle is
calculated by "high_width / (period + 1)". If period is the "magic
number 0xfff", high_width needs 13 bits to show the situation that duty
cycle is 100%. I should fix the formula for high_width below.
> > +struct mtk_disp_pwm {
> > + struct pwm_chip chip;
> > + struct device *dev;
> > + struct clk *clk_main;
> > + struct clk *clk_mm;
> > + void __iomem *mmio_base;
>
> I think "base" will do just fine.
>
OK.
> > +};
> > +
> > +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)
> > +{
> > + 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;
> > + 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
>
> Nit: should have a space between '+' and '1'.
>
OK.
> > + * duty_ns = 10^9 * (clk_div + 1) * (high_width + 1) / PWM_CLK_RATE
Here should be
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)) - 1
And here
high_width = (PWM_CLK_RATE * duty_ns) / (10^9 * (clk_div + 1))
> > + */
> > + mdp = to_mtk_disp_pwm(chip);
>
> Please put this on the same line as the variable declaration:
>
> struct mtk_disp_pwm *mdp = to_mtk_disp_pwm(chip);
>
OK.
> > + 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 = clk_div + 1;
>
> Perhaps make this:
>
> div = NSEC_PER_SEC * (clk_div + 1);
>
> to avoid the two multiplication below.
>
You are right.
> > + period = div64_u64(rate * period_ns, NSEC_PER_SEC * div);
>
> So this would become:
>
> period = div64_u64(rate * period_ns, div);
>
Got it.
> > + if (period > 0)
> > + period--;
> > +
> > + high_width = div64_u64(rate * duty_ns, NSEC_PER_SEC * div);
>
> And this:
>
> high_width = div64_u64(rate * duty_ns, div);
>
OK.
> > + if (high_width > 0)
> > + high_width--;
I should remove this two lines above for the new formula.
> > +
> > + mtk_disp_pwm_update_bits(mdp->mmio_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->mmio_base + DISP_PWM_CON_1,
> > + PWM_PERIOD_MASK | PWM_HIGH_WIDTH_MASK, value);
> > +
> > + mtk_disp_pwm_update_bits(mdp->mmio_base + DISP_PWM_COMMIT,
> > + PWM_COMMIT_MASK, 1);
> > + mtk_disp_pwm_update_bits(mdp->mmio_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;
> > +
> > + mdp = to_mtk_disp_pwm(chip);
>
> The above three lines should be collapsed.
>
OK.
> > + mtk_disp_pwm_update_bits(mdp->mmio_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;
> > +
> > + mdp = to_mtk_disp_pwm(chip);
>
> Same here.
>
OK.
> > + mtk_disp_pwm_update_bits(mdp->mmio_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->mmio_base = devm_ioremap_resource(&pdev->dev, r);
> > + if (IS_ERR(mdp->mmio_base))
> > + return PTR_ERR(mdp->mmio_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);
> > + if (ret < 0)
> > + return ret;
> > +
> > + ret = clk_prepare_enable(mdp->clk_mm);
> > + if (ret < 0) {
> > + clk_disable_unprepare(mdp->clk_main);
> > + return ret;
> > + }
> > +
> > + platform_set_drvdata(pdev, mdp);
> > +
> > + 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);
> > + clk_disable_unprepare(mdp->clk_main);
> > + clk_disable_unprepare(mdp->clk_mm);
> > + return ret;
> > + }
> > +
> > + return 0;
> > +}
>
> It's customary to collect the error cleanup code in an unwinding section
> at the bottom of the function, like so:
>
> ret = clk_prepare_enable(mdp->clk_mm);
> if (ret < 0)
> goto disable_clk_main;
>
> ...
>
> ret = pwmchip_add(&mdp->chip);
> if (ret < 0) {
> dev_err(&pdev->dev, ...);
> 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;
>
> This makes sure that you undo things in the proper order and eliminates
> the need to duplicate cleanup code in all failure paths.
>
I will rewrite this part.
> > +
> > +static int mtk_disp_pwm_remove(struct platform_device *pdev)
> > +{
> > + struct mtk_disp_pwm *mdp;
> > + int ret;
> > +
> > + mdp = platform_get_drvdata(pdev);
>
> Should be on the same line as the variable declaration.
>
OK.
> > + ret = pwmchip_remove(&mdp->chip);
> > + clk_disable_unprepare(mdp->clk_main);
> > + clk_disable_unprepare(mdp->clk_mm);
> > +
> > + 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);
> > +
> > +static struct platform_driver mtk_disp_pwm_driver = {
> > + .driver = {
> > + .name = "mediatek-disp-pwm",
> > + .of_match_table = mtk_disp_pwm_of_match,
> > + },
> > + .probe = mtk_disp_pwm_probe,
> > + .remove = mtk_disp_pwm_remove,
> > +};
> > +module_platform_driver(mtk_disp_pwm_driver);
> > +
> > +MODULE_AUTHOR("YH Huang <yh.huang@xxxxxxxxxxxx>");
> > +MODULE_DESCRIPTION("MediaTek SoC display PWM driver");
> > +MODULE_LICENSE("GPL v2");
>
> Thierry
Thank for your suggestion.
Regards,
YH Huang
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