RE: [EXT] Re: [v9 2/2] clk: ls1028a: Add clock driver for Display output interface

[Wen He <wen.he_1@nxp.com>]

> -----Original Message-----
> From: Michael Walle <michael@walle.cc>
> Sent: 2019年11月20日 22:36
> To: Wen He <wen.he_1@nxp.com>
> Cc: devicetree@vger.kernel.org; Leo Li <leoyang.li@nxp.com>;
> linux-clk@vger.kernel.org; linux-kernel@vger.kernel.org;
> mark.rutland@arm.com; mturquette@baylibre.com; robh+dt@kernel.org;
> sboyd@kernel.org
> Subject: [EXT] Re: [v9 2/2] clk: ls1028a: Add clock driver for Display output
> interface
> 
> 
> Hi,

Hi Michael,

> 
> > Add clock driver for QorIQ LS1028A Display output interfaces(LCD,
> > DPHY), as implemented in TSMC CLN28HPM PLL, this PLL supports the
> > programmable integer division and range of the display output pixel
> > clock's 27-594MHz.
> >
> > Signed-off-by: Wen He <wen.he_1@nxp.com>
> > ---
> > change in v9:
> >       - Use the fixed mfd in plldig_set_rate
> >
> >  drivers/clk/Kconfig      |  10 ++
> >  drivers/clk/Makefile     |   1 +
> >  drivers/clk/clk-plldig.c | 297
> > +++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 308 insertions(+)
> >  create mode 100644 drivers/clk/clk-plldig.c
> >
> > diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig index
> > 0530bebfc25a..9f6b0196c604 100644
> > --- a/drivers/clk/Kconfig
> > +++ b/drivers/clk/Kconfig
> > @@ -218,6 +218,16 @@ config CLK_QORIQ
> >         This adds the clock driver support for Freescale QorIQ platforms
> >         using common clock framework.
> >
> > +config CLK_LS1028A_PLLDIG
> > +        tristate "Clock driver for LS1028A Display output"
> > +        depends on ARCH_LAYERSCAPE || COMPILE_TEST
> > +        default ARCH_LAYERSCAPE
> > +        help
> > +          This driver support the Display output interfaces(LCD,
> > +DPHY)
> > pixel clocks
> > +          of the QorIQ Layerscape LS1028A, as implemented TSMC
> > CLN28HPM PLL. Not all
> > +          features of the PLL are currently supported by the driver.
> > By default,
> > +          configured bypass mode with this PLL.
> > +
> >  config COMMON_CLK_XGENE
> >       bool "Clock driver for APM XGene SoC"
> >       default ARCH_XGENE
> > diff --git a/drivers/clk/Makefile b/drivers/clk/Makefile index
> > 0138fb14e6f8..97d1e5bc6de5 100644
> > --- a/drivers/clk/Makefile
> > +++ b/drivers/clk/Makefile
> > @@ -43,6 +43,7 @@ obj-$(CONFIG_ARCH_NPCM7XX)          +=
> clk-npcm7xx.o
> >  obj-$(CONFIG_ARCH_NSPIRE)            += clk-nspire.o
> >  obj-$(CONFIG_COMMON_CLK_OXNAS)               += clk-oxnas.o
> >  obj-$(CONFIG_COMMON_CLK_PALMAS)              += clk-palmas.o
> > +obj-$(CONFIG_CLK_LS1028A_PLLDIG)     += clk-plldig.o
> >  obj-$(CONFIG_COMMON_CLK_PWM)         += clk-pwm.o
> >  obj-$(CONFIG_CLK_QORIQ)                      += clk-qoriq.o
> >  obj-$(CONFIG_COMMON_CLK_RK808)               += clk-rk808.o
> > diff --git a/drivers/clk/clk-plldig.c b/drivers/clk/clk-plldig.c new
> > file mode 100644 index 000000000000..f940a9d3d011
> > --- /dev/null
> > +++ b/drivers/clk/clk-plldig.c
> > @@ -0,0 +1,297 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright 2019 NXP
> > + *
> > + * Clock driver for LS1028A Display output interfaces(LCD, DPHY).
> > + */
> > +
> > +#include <linux/clk-provider.h>
> > +#include <linux/device.h>
> > +#include <linux/module.h>
> > +#include <linux/err.h>
> > +#include <linux/io.h>
> > +#include <linux/iopoll.h>
> > +#include <linux/of.h>
> > +#include <linux/of_address.h>
> > +#include <linux/of_device.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/slab.h>
> > +#include <linux/bitfield.h>
> > +
> > +/* PLLDIG register offsets and bit masks */
> > +#define PLLDIG_REG_PLLSR            0x24
> > +#define PLLDIG_REG_PLLDV            0x28
> > +#define PLLDIG_REG_PLLFM            0x2c
> > +#define PLLDIG_REG_PLLFD            0x30
> > +#define PLLDIG_REG_PLLCAL1          0x38
> > +#define PLLDIG_REG_PLLCAL2          0x3c
> > +#define PLLDIG_LOCK_MASK            BIT(2)
> > +#define PLLDIG_REG_FIELD_SSCGBYP    BIT(30)
> > +#define PLLDIG_REG_FIELD_FDEN       BIT(30)
> > +#define PLLDIG_REG_FIELD_DTHDIS     GENMASK(17, 16)
> > +#define PLLDIG_REG_FIELD_MULT       GENMASK(7, 0)
> > +#define PLLDIG_REG_FIELD_RFDPHI1    GENMASK(30, 25)
> > +
> > +/* Minimum output clock frequency, in Hz */ #define PHI1_MIN_FREQ
> > +27000000
> > +
> > +/* Maximum output clock frequency, in Hz */ #define PHI1_MAX_FREQ
> > +600000000
> > +
> > +/* Maximum of the divider */
> > +#define MAX_RFDPHI1          63
> > +
> > +/*
> > + * Clock configuration relationship between the PHI1
> > frequency(fpll_phi) and
> > + * the output frequency of the PLL is determined by the PLLDV,
> > according to
> > + * the following equation:
> > + * fpll_phi = (pll_ref * mfd) / div_rfdphi1  */ struct
> > +plldig_phi1_param {
> > +     unsigned long rate;
> > +     unsigned int rfdphi1;
> > +     unsigned int mfd;
> > +};
> > +
> > +static const struct clk_parent_data parent_data[] = {
> > +     {.index = 0},
> > +};
> > +
> > +struct clk_plldig {
> > +     struct clk_hw hw;
> > +     void __iomem *regs;
> > +     unsigned int mfd;
> > +};
> > +
> > +#define to_clk_plldig(_hw)   container_of(_hw, struct clk_plldig, hw)
> > +
> > +static int plldig_enable(struct clk_hw *hw) {
> > +     struct clk_plldig *data = to_clk_plldig(hw);
> > +     u32 val;
> > +
> > +     val = readl(data->regs + PLLDIG_REG_PLLFM);
> > +     /*
> > +      * Use Bypass mode with PLL off by default, the frequency overshoot
> > +      * detector output was disable. SSCG Bypass mode should be enable.
> > +      */
> > +     val |= PLLDIG_REG_FIELD_SSCGBYP;
> > +     writel(val, data->regs + PLLDIG_REG_PLLFM);
> > +
> > +     val = readl(data->regs + PLLDIG_REG_PLLFD);
> > +     /* Disable dither and Sigma delta modulation in bypass mode */
> > +     val |= FIELD_PREP(PLLDIG_REG_FIELD_FDEN, 0x1) |
> 
> Unlike mentioned in the documentation, FDEN is "fractional divider enable".
> 
> 

Yes, this point just confirmed in yesterday.

> 
> > +            FIELD_PREP(PLLDIG_REG_FIELD_DTHDIS, 0x3);
> > +
> > +     writel(val, data->regs + PLLDIG_REG_PLLFD);
> > +
> > +     return 0;
> > +}
> > +
> > +static void plldig_disable(struct clk_hw *hw) {
> > +     struct clk_plldig *data = to_clk_plldig(hw);
> > +     u32 val;
> > +
> > +     val = readl(data->regs + PLLDIG_REG_PLLFM);
> > +
> > +     val &= ~PLLDIG_REG_FIELD_SSCGBYP;
> > +     val |= FIELD_PREP(PLLDIG_REG_FIELD_SSCGBYP, 0x0);
> > +
> > +     writel(val, data->regs + PLLDIG_REG_PLLFM); }
> > +
> > +static int plldig_is_enabled(struct clk_hw *hw) {
> > +     struct clk_plldig *data = to_clk_plldig(hw);
> > +
> > +     return (readl(data->regs + PLLDIG_REG_PLLFM) &
> > +                           PLLDIG_REG_FIELD_SSCGBYP); }
> > +
> > +static unsigned long plldig_recalc_rate(struct clk_hw *hw,
> > +             unsigned long parent_rate) {
> > +     struct clk_plldig *data = to_clk_plldig(hw);
> > +     u32 mult, div, val;
> > +
> > +     val = readl(data->regs + PLLDIG_REG_PLLDV);
> > +
> > +     /* Check if PLL is bypassed */
> > +     if (val & PLLDIG_REG_FIELD_SSCGBYP)
> > +             return parent_rate;
> > +
> > +     /* Checkout multiplication factor divider value */
> > +     mult = FIELD_GET(PLLDIG_REG_FIELD_MULT, val);
> > +
> > +     /* Checkout divider value of the output frequency */
> > +     div = FIELD_GET(PLLDIG_REG_FIELD_RFDPHI1, val);
> > +
> > +     return (parent_rate * mult) / div; }
> > +
> > +static int plldig_calc_target_rate(unsigned long target_rate,
> > +                                unsigned long parent_rate,
> > +                                struct plldig_phi1_param *phi1) {
> > +     unsigned int div, ret;
> > +     unsigned long round_rate;
> > +
> > +     /* Range limitation of the request target rate */
> > +     if (target_rate > PHI1_MAX_FREQ)
> > +             target_rate = PHI1_MAX_FREQ;
> > +     else if (target_rate < PHI1_MIN_FREQ)
> > +             target_rate = PHI1_MIN_FREQ;
> > +
> > +     /*
> > +      * Firstly, check the request target rate whether is divisible
> > +      * by the best VCO frequency.
> > +      */
> > +     round_rate = parent_rate * phi1->mfd;
> > +     div = round_rate / target_rate;
> Can't you use DIV_ROUND_UP(), DIV_ROUND_DOWN_ULL() or
> DIV_ROUND_CLOSEST_ULL() and drop the stuff below except the range check?
> 

Great advice.

> 
> > +     if (!div || div > MAX_RFDPHI1)
> > +             return -EINVAL;
> > +
> > +     ret = round_rate % target_rate;
> > +     if (ret) {
> > +             /*
> > +              * Rounded down the request target rate, VESA specifies
> > +              * 0.5% pixel clock tolerance, therefore this algorithm
> > +              * can able to compatible a lot of request rates within
> > +              * range of the tolerance.
> > +              */
> > +             round_rate += (target_rate / 2);
> > +             div = round_rate / target_rate;
> > +             if (!div || div > MAX_RFDPHI1)
> > +                     return -EINVAL;
> > +     }
> > +
> > +     phi1->rfdphi1 = div;
> > +     phi1->rate = target_rate;
> > +
> > +     return 0;
> > +}
> > +
> > +static int plldig_determine_rate(struct clk_hw *hw,
> > +                              struct clk_rate_request *req) {
> > +     int ret;
> > +     unsigned long parent_rate;
> > +     struct clk_hw *parent;
> > +     struct plldig_phi1_param phi1_param;
> > +     struct clk_plldig *data = to_clk_plldig(hw);
> > +
> > +     if (!req->rate)
> > +             return -ERANGE;
> > +
> > +     phi1_param.mfd = data->mfd;
> > +     parent = clk_hw_get_parent(hw);
> > +     parent_rate = clk_hw_get_rate(parent);
> > +
> > +     ret = plldig_calc_target_rate(req->rate, parent_rate, &phi1_param);
> > +     if (ret)
> > +             return ret;
> > +
> > +     req->rate = phi1_param.rate;
> > +
> > +     return 0;
> > +}
> > +
> > +static int plldig_set_rate(struct clk_hw *hw, unsigned long rate,
> > +             unsigned long parent_rate) {
> > +     struct clk_plldig *data = to_clk_plldig(hw);
> > +     struct plldig_phi1_param phi1_param;
> > +     unsigned int val, cond;
> > +     int ret;
> > +
> > +     phi1_param.mfd = data->mfd;
> > +     ret = plldig_calc_target_rate(rate, parent_rate, &phi1_param);
> > +     if (ret)
> > +             return ret;
> > +
> > +     val = readl(data->regs + PLLDIG_REG_PLLDV);
> > +     val = FIELD_PREP(PLLDIG_REG_FIELD_MULT, phi1_param.mfd) |
> > +           FIELD_PREP(PLLDIG_REG_FIELD_RFDPHI1,
> phi1_param.rfdphi1);
> > +
> > +     writel(val, data->regs + PLLDIG_REG_PLLDV);
> > +
> > +     /* delay 200us make sure that old lock state is cleared */
> > +     udelay(200);
> > +
> > +     /* Wait until PLL is locked or timeout (maximum 1000 usecs) */
> > +     return readl_poll_timeout_atomic(data->regs + PLLDIG_REG_PLLSR,
> cond,
> > +                                      cond & PLLDIG_LOCK_MASK, 0,
> > +                                      USEC_PER_MSEC); }
> > +
> > +static const struct clk_ops plldig_clk_ops = {
> > +     .enable = plldig_enable,
> > +     .disable = plldig_disable,
> > +     .is_enabled = plldig_is_enabled,
> > +     .recalc_rate = plldig_recalc_rate,
> > +     .determine_rate = plldig_determine_rate,
> > +     .set_rate = plldig_set_rate,
> > +};
> > +
> > +static int plldig_clk_probe(struct platform_device *pdev) {
> > +     struct clk_plldig *data;
> > +     struct resource *mem;
> > +     struct device *dev = &pdev->dev;
> > +     int ret;
> > +
> > +     data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
> > +     if (!data)
> > +             return -ENOMEM;
> > +
> > +     mem = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +     data->regs = devm_ioremap_resource(dev, mem);
> > +     if (IS_ERR(data->regs))
> > +             return PTR_ERR(data->regs);
> > +
> > +      /*
> > +       * Support to get the best loop multiplication divider value
> > +       * from DTS file, since this PLL can't changed this value on
> > +       * the fly, write the fixed value.
> > +       */
> > +     ret = of_property_read_u32(dev->of_node, "best-mfd", &data->mfd);
> > +     if (ret)
> > +             data->mfd = 0x2c;
> 
> IMHO this is a really bad device tree binding. First it is not described anywhere,
> ie it is missing in the dt-bindings file and second, to actually make use of the
> "best-mfd" the user has to know the parent clock, the desired vco frequency
> and have to calculate it by himself.
> IMHO a better one would be something like "vco-frequency". Also you should
> use the fractional divider to get better results. Using the fractional divider
> almost any VCO frequency is possible (within a certain range which should be
> checked [650 MHz to 1300 MHz]).
> 

Yes, the fractional part can covered range is 27MHz, it can almost any VCO frequency. 
the fractional divider should be supported in this driver.

I also knew the device tree binding is bad specially way, but here just want to
provide a simple solution used to configure the MFD value for users requirement.
So you think that should be use "vco-frequency" instead of the "best-mfd" in dts used to
avoid user recalculate it(user may don’t know the parent rate)?

Best Regards,
Wen

> 
> > +
> > +     writel(data->mfd, data->regs + PLLDIG_REG_PLLDV);
> > +
> > +     data->hw.init = CLK_HW_INIT_PARENTS_DATA("dpclk",
> > +                                              parent_data,
> > +                                              &plldig_clk_ops,
> > +                                              0);
> > +
> > +     ret = devm_clk_hw_register(dev, &data->hw);
> > +     if (ret) {
> > +             dev_err(dev, "failed to register %s clock\n",
> > +                                             dev->of_node->name);
> > +             return ret;
> > +     }
> > +
> > +     return devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get,
> > +                                        &data->hw); }
> > +
> > +static const struct of_device_id plldig_clk_id[] = {
> > +     { .compatible = "fsl,ls1028a-plldig"},
> > +     { }
> > +};
> > +MODULE_DEVICE_TABLE(of, plldig_clk_id);
> > +
> > +static struct platform_driver plldig_clk_driver = {
> > +     .driver = {
> > +             .name = "plldig-clock",
> > +             .of_match_table = plldig_clk_id,
> > +     },
> > +     .probe = plldig_clk_probe,
> > +};
> > +module_platform_driver(plldig_clk_driver);
> > +
> > +MODULE_LICENSE("GPL v2");
> > +MODULE_AUTHOR("Wen He <wen.he_1@nxp.com>");
> > +MODULE_DESCRIPTION("LS1028A Display output interface pixel clock
> > driver");
> 
> -michael