Date:   Wed, 18 Sep 2019 09:20:26 +0000
From:   Wen He <wen.he_1@....com>
To:     Stephen Boyd <sboyd@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-clk@...r.kernel.org" <linux-clk@...r.kernel.org>,
        "linux-devel@...ux.nxdi.nxp.com" <linux-devel@...ux.nxdi.nxp.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
CC:     Leo Li <leoyang.li@....com>,
        "liviu.dudau@....com" <liviu.dudau@....com>
Subject: RE: [EXT] Re: [v4 2/2] clk: ls1028a: Add clock driver for Display
 output interface



> -----Original Message-----
> From: Stephen Boyd <sboyd@...nel.org>
> Sent: 2019年9月17日 4:27
> To: Mark Rutland <mark.rutland@....com>; Michael Turquette
> <mturquette@...libre.com>; Rob Herring <robh+dt@...nel.org>; Wen He
> <wen.he_1@....com>; devicetree@...r.kernel.org; linux-clk@...r.kernel.org;
> linux-devel@...ux.nxdi.nxp.com; linux-kernel@...r.kernel.org
> Cc: Leo Li <leoyang.li@....com>; liviu.dudau@....com; Wen He
> <wen.he_1@....com>
> Subject: [EXT] Re: [v4 2/2] clk: ls1028a: Add clock driver for Display output
> interface
> 
> 
> Quoting Wen He (2019-08-29 03:59:19)
> > diff --git a/drivers/clk/Kconfig b/drivers/clk/Kconfig index
> > 801fa1cd0321..ab05f342af04 100644
> > --- a/drivers/clk/Kconfig
> > +++ b/drivers/clk/Kconfig
> > @@ -223,6 +223,16 @@ config CLK_QORIQ
> >           This adds the clock driver support for Freescale QorIQ platforms
> >           using common clock framework.
> >
> > +config CLK_LS1028A_PLLDIG
> > +        bool "Clock driver for LS1028A Display output"
> 
> Is this a tristate? The driver is made to be a module but it isn't allowed to be
> compiled as such.
> 
> > +        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/clk-plldig.c b/drivers/clk/clk-plldig.c new
> > file mode 100644 index 000000000000..d3239bcf59de
> > --- /dev/null
> > +++ b/drivers/clk/clk-plldig.c
> > @@ -0,0 +1,298 @@
> > +// 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>
> > +
> > +/* 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_SSCGBYP_ENABLE       BIT(30)
> > +#define PLLDIG_FDEN                 BIT(30)
> > +#define PLLDIG_DTHRCTL              (0x3 << 16)
> > +
> > +/* macro to get/set values into register */
> > +#define PLLDIG_GET_MULT(x)          (((x) & ~(0xffffff00)) << 0)
> > +#define PLLDIG_GET_RFDPHI1(x)       ((u32)(x) >> 25)
> > +#define PLLDIG_SET_RFDPHI1(x)       ((u32)(x) << 25)
> 
> Maybe you can use the FIELD_GET() APIs and genmask from bitfield.h?

Hmm, that a good idea. 

> 
> > +
> > +/* Maximum of the divider */
> > +#define MAX_RFDPHI1          63
> > +
> > +/* Best value of multiplication factor divider */
> > +#define PLLDIG_DEFAULE_MULT         44
> > +
> > +/*
> > + * 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;
> > +};
> > +
> > +enum plldig_phi1_freq_range {
> > +       PHI1_MIN        = 27000000U,
> > +       PHI1_MAX        = 600000000U
> > +};
> 
> Please just inline these values in the one place they're used.
> 
> > +
> > +struct clk_plldig {
> > +       struct clk_hw hw;
> > +       void __iomem *regs;
> > +       struct device *dev;
> 
> Please remove this, it is unused.

It is used for probe.

> 
> > +};
> > +
> > +#define to_clk_plldig(_hw)     container_of(_hw, struct clk_plldig, hw)
> > +#define LOCK_TIMEOUT_US                USEC_PER_MSEC
> 
> Is this used?

Yes, it is used.

> 
> > +
> > +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_SSCGBYP_ENABLE;
> > +       writel(val, data->regs + PLLDIG_REG_PLLFM);
> > +
> > +       val = readl(data->regs + PLLDIG_REG_PLLFD);
> > +       /* Disable dither and Sigma delta modulation in bypass mode */
> > +       val |= (PLLDIG_FDEN | PLLDIG_DTHRCTL);
> > +       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_SSCGBYP_ENABLE;
> > +       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_SSCGBYP_ENABLE); }
> > +
> > +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_SSCGBYP_ENABLE)
> > +               return parent_rate;
> > +
> > +       /* Checkout multiplication factor divider value */
> > +       mult = val;
> > +       mult = PLLDIG_GET_MULT(mult);
> > +
> > +       /* Checkout divider value of the output frequency */
> > +       div = val;
> > +       div = PLLDIG_GET_RFDPHI1(div);
> > +
> > +       return (parent_rate * mult) / div; }
> > +
> > +static int plldig_calc_target_rate(unsigned long target_rate,
> > +                                  unsigned long parent_rate,
> > +                                  struct plldig_phi1_param
> *phi1_out)
> > +{
> > +       unsigned int div, mfd, ret;
> > +       unsigned long round_rate;
> > +
> > +       /*
> > +        * Firstly, check the target rate whether is divisible
> > +        * by the best VCO frequency.
> > +        */
> > +       mfd = PLLDIG_DEFAULE_MULT;
> > +       round_rate = parent_rate * mfd;
> > +       div = round_rate / target_rate;
> > +       if (!div || div > MAX_RFDPHI1)
> > +               return -EINVAL;
> > +
> > +       ret = round_rate % target_rate;
> > +       if (!ret)
> > +               goto out;
> 
> Please get rid of ret and do the test here directly and then put the below code
> into the if statement to remove the goto.

Here provide two condition to test the request target rate whether meet.
1. always check the request rate whether is divisible by the VCO frequency.
2. If option#1 is not meet, trying to rounding.

Option#1 and option#2 both need use the below code, if remove the goto, will
see the duplicate code statement.

> 
> 
>         if (round_rate % target_rate) {
>                /*
>                 * Otherwise, try a rounding algorithm to driven the target
> rate,
>                 * this algorithm allows tolerances between the target rate
> and
>                 * real rate, it based on the best VCO output frequency.
>                 */
>                mfd = PLLDIG_DEFAULE_MULT;
>                round_rate = parent_rate * mfd;
> 
>                /*
>                 * Add half of the target rate so the result will be
>                 * rounded to cloeset instead of rounded down.
>                 */
>                round_rate += (target_rate / 2);
>                div = round_rate / target_rate;
>                if (!div || div > MAX_RFDPHI1)
>                        return -EINVAL;
> 
>         }
> 
> > +       phi1_out->rfdphi1 = PLLDIG_SET_RFDPHI1(div);
> > +       phi1_out->mfd = mfd;
> > +       phi1_out->rate = target_rate;
> > +
> > +       return 0;
> > +}
> > +
> > +static int plldig_determine_rate(struct clk_hw *hw,
> > +                                struct clk_rate_request *req) {
> > +       int ret;
> > +       struct clk_hw *parent;
> > +       struct plldig_phi1_param phi1_param;
> > +       unsigned long parent_rate;
> > +
> > +       if (req->rate == 0 || req->rate < PHI1_MIN || req->rate >
> PHI1_MAX)
> > +               return -EINVAL;
> 
> Preferably you clamp the requested rate to min/max instead of just returning a
> failure. That way the clk_set_rate() API "works" by trying to achieve some
> frequency that is there. You'll have to look at the request that is passed into
> this function to make sure that the min/max of the request is within the range
> this clk supports, but it will be better than just blindly returning a failure
> because this function should try to round the rate to something that is
> supported.

I agree with you.

> 
> > +
> > +       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 rfdphi1, val, cond;
> > +       int ret = -ETIMEDOUT;
> 
> Drop this initial assignment please.
> 
> > +
> > +       ret = plldig_calc_target_rate(rate, parent_rate, &phi1_param);
> > +       if (ret)
> > +               return ret;
> 
> Because it's overwritten immediately.
> 
> > +
> > +       val = readl(data->regs + PLLDIG_REG_PLLDV);
> > +       val = phi1_param.mfd;
> > +       rfdphi1 = phi1_param.rfdphi1;
> > +       val |= 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) */
> > +       ret = readl_poll_timeout_atomic(data->regs + PLLDIG_REG_PLLSR,
> cond,
> > +                                       cond & PLLDIG_LOCK_MASK,
> 0,
> > +                                       USEC_PER_MSEC);
> > +
> > +       return ret;
> 
> Just return readl_poll_timeout_atomic(...) here.

Maybe use below code will to best describes.

If (ret)
	return -ETIMEOUT;

return 0;

> 
> > +}
> > +
> > +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 clk_init_data init = {};
> > +       struct device *dev = &pdev->dev;
> > +       struct clk_parent_data parent_data;
> 
> Set this to = { .index = 0 }

Understand,

> 
> > +       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);
> > +
> > +       parent_data.name = of_clk_get_parent_name(dev->of_node, 0);
> > +       parent_data.index = 0;
> 
> And don't assign these.

Understand,

> 
> > +
> > +       init.name = dev->of_node->name;
> > +       init.ops = &plldig_clk_ops;
> > +       init.parent_data = &parent_data;
> > +       init.num_parents = 1;
> > +
> > +       data->hw.init = &init;
> > +       data->dev = dev;
> > +
> > +       ret = devm_clk_hw_register(dev, &data->hw);
> > +       if (ret) {
> > +               dev_err(dev, "failed to register %s clock\n", init.name);
> > +               return ret;
> > +       }
> > +
> > +       ret = devm_of_clk_add_hw_provider(dev, of_clk_hw_simple_get,
> &data->hw);
> > +       if (ret)
> > +               dev_err(dev, "failed adding the clock provider\n");
> > +
> > +       return ret;
> 
> I'd prefer to just see return devm_of_clk_add_hw_provider(), but not a big
> deal.

Understand, thank you for the review.

Best Regards,
Wen

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