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SubjectRe: [PATCH v10 3/3] pwm: Add support for Xilinx AXI Timer
Date
Hi Uwe,

On 11/18/21 4:28 AM, Uwe Kleine-König wrote:
> Hello,
>
> On Fri, Nov 12, 2021 at 01:55:04PM -0500, Sean Anderson wrote:
>> This adds PWM support for Xilinx LogiCORE IP AXI soft timers commonly
>> found on Xilinx FPGAs. At the moment clock control is very basic: we
>> just enable the clock during probe and pin the frequency. In the future,
>> someone could add support for disabling the clock when not in use.
>>
>> Some common code has been specially demarcated. While currently only
>> used by the PWM driver, it is anticipated that it may be split off in
>> the future to be used by the timer driver as well.
>>
>> This driver was written with reference to Xilinx DS764 for v1.03.a [1].
>>
>> [1] https://www.xilinx.com/support/documentation/ip_documentation/axi_timer/v1_03_a/axi_timer_ds764.pdf
>>
>> Signed-off-by: Sean Anderson <sean.anderson@seco.com>
>> ---
>>
>> Changes in v10:
>> - Fix compilation error in timer driver
>>
>> Changes in v9:
>> - Refactor "if { return } else if { }" to "if { return } if { }"
>> - Remove drivers/clocksource/timer-xilinx-common.c from MAINTAINERS
>> - Remove xilinx_timer_common_init and integrate it into xilinx_timer_probe
>>
>> Changes in v8:
>> - Drop new timer driver; it has been deferred for future series
>>
>> Changes in v7:
>> - Add dependency on OF_ADDRESS
>> - Fix period_cycles calculation
>> - Fix typo in limitations
>>
>> Changes in v6:
>> - Capitalize error messages
>> - Don't disable regmap locking to allow inspection of registers via
>> debugfs
>> - Prevent overflow when calculating period_cycles
>> - Remove enabled variable from xilinx_pwm_apply
>> - Swap order of period_cycle range comparisons
>>
>> Changes in v5:
>> - Allow non-zero #pwm-cells
>> - Correctly set duty_cycle in get_state when TLR0=TLR1
>> - Elaborate on limitation section
>> - Perform some additional checks/rounding in apply_state
>> - Remove xlnx,axi-timer-2.0 compatible string
>> - Rework duty-cycle and period calculations with feedback from Uwe
>> - Switch to regmap to abstract endianness issues
>> - Use more verbose error messages
>>
>> Changes in v4:
>> - Don't use volatile in read/write replacements. Some arches have it and
>> some don't.
>> - Put common timer properties into their own struct to better reuse
>> code.
>> - Remove references to properties which are not good enough for Linux.
>>
>> Changes in v3:
>> - Add clockevent and clocksource support
>> - Remove old microblaze driver
>> - Rewrite probe to only use a device_node, since timers may need to be
>> initialized before we have proper devices. This does bloat the code a bit
>> since we can no longer rely on helpers such as dev_err_probe. We also
>> cannot rely on device resources being free'd on failure, so we must free
>> them manually.
>> - We now access registers through xilinx_timer_(read|write). This allows us
>> to deal with endianness issues, as originally seen in the microblaze
>> driver. CAVEAT EMPTOR: I have not tested this on big-endian!
>>
>> Changes in v2:
>> - Add comment describing device
>> - Add comment explaining why we depend on !MICROBLAZE
>> - Add dependencies on COMMON_CLK and HAS_IOMEM
>> - Cast dividends to u64 to avoid overflow
>> - Check for over- and underflow when calculating TLR
>> - Check range of xlnx,count-width
>> - Don't compile this module by default for arm64
>> - Don't set pwmchip.base to -1
>> - Ensure the clock is always running when the pwm is registered
>> - Remove debugfs file :l
>> - Rename TCSR_(SET|CLEAR) to TCSR_RUN_(SET|CLEAR)
>> - Report errors with dev_error_probe
>> - Set xilinx_pwm_ops.owner
>> - Use NSEC_TO_SEC instead of defining our own
>> - Use TCSR_RUN_MASK to check if the PWM is enabled, as suggested by Uwe
>>
>> MAINTAINERS | 6 +
>> arch/microblaze/kernel/timer.c | 3 +
>> drivers/pwm/Kconfig | 14 ++
>> drivers/pwm/Makefile | 1 +
>> drivers/pwm/pwm-xilinx.c | 311 +++++++++++++++++++++++++++++
>> include/clocksource/timer-xilinx.h | 91 +++++++++
>> 6 files changed, 426 insertions(+)
>> create mode 100644 drivers/pwm/pwm-xilinx.c
>> create mode 100644 include/clocksource/timer-xilinx.h
>>
>> diff --git a/MAINTAINERS b/MAINTAINERS
>> index 3b79fd441dde..6f0f57c041c4 100644
>> --- a/MAINTAINERS
>> +++ b/MAINTAINERS
>> @@ -20614,6 +20614,12 @@ F: drivers/misc/Makefile
>> F: drivers/misc/xilinx_sdfec.c
>> F: include/uapi/misc/xilinx_sdfec.h
>>
>> +XILINX PWM DRIVER
>> +M: Sean Anderson <sean.anderson@seco.com>
>> +S: Maintained
>> +F: drivers/pwm/pwm-xilinx.c
>> +F: include/clocksource/timer-xilinx.h
>> +
>> XILINX UARTLITE SERIAL DRIVER
>> M: Peter Korsgaard <jacmet@sunsite.dk>
>> L: linux-serial@vger.kernel.org
>> diff --git a/arch/microblaze/kernel/timer.c b/arch/microblaze/kernel/timer.c
>> index f8832cf49384..dea34a3d4aa4 100644
>> --- a/arch/microblaze/kernel/timer.c
>> +++ b/arch/microblaze/kernel/timer.c
>> @@ -251,6 +251,9 @@ static int __init xilinx_timer_init(struct device_node *timer)
>> u32 timer_num = 1;
>> int ret;
>>
>> + if (of_property_read_bool(timer, "#pwm-cells"))
>> + return 0;
>> +
>> if (initialized)
>> return -EINVAL;
>>
>> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
>> index aa29841bbb79..47f25237754f 100644
>> --- a/drivers/pwm/Kconfig
>> +++ b/drivers/pwm/Kconfig
>> @@ -638,4 +638,18 @@ config PWM_VT8500
>> To compile this driver as a module, choose M here: the module
>> will be called pwm-vt8500.
>>
>> +config PWM_XILINX
>> + tristate "Xilinx AXI Timer PWM support"
>> + depends on OF_ADDRESS
>> + depends on COMMON_CLK
>> + select REGMAP_MMIO
>> + help
>> + PWM driver for Xilinx LogiCORE IP AXI timers. This timer is
>> + typically a soft core which may be present in Xilinx FPGAs.
>> + This device may also be present in Microblaze soft processors.
>> + If you don't have this IP in your design, choose N.
>> +
>> + To compile this driver as a module, choose M here: the module
>> + will be called pwm-xilinx.
>> +
>> endif
>> diff --git a/drivers/pwm/Makefile b/drivers/pwm/Makefile
>> index 708840b7fba8..ea785480359b 100644
>> --- a/drivers/pwm/Makefile
>> +++ b/drivers/pwm/Makefile
>> @@ -60,3 +60,4 @@ obj-$(CONFIG_PWM_TWL) += pwm-twl.o
>> obj-$(CONFIG_PWM_TWL_LED) += pwm-twl-led.o
>> obj-$(CONFIG_PWM_VISCONTI) += pwm-visconti.o
>> obj-$(CONFIG_PWM_VT8500) += pwm-vt8500.o
>> +obj-$(CONFIG_PWM_XILINX) += pwm-xilinx.o
>> diff --git a/drivers/pwm/pwm-xilinx.c b/drivers/pwm/pwm-xilinx.c
>> new file mode 100644
>> index 000000000000..d79ef202d62f
>> --- /dev/null
>> +++ b/drivers/pwm/pwm-xilinx.c
>> @@ -0,0 +1,311 @@
>> +// SPDX-License-Identifier: GPL-2.0+
>> +/*
>> + * Copyright (C) 2021 Sean Anderson <sean.anderson@seco.com>
>> + *
>> + * Limitations:
>> + * - When changing both duty cycle and period, we may end up with one cycle
>> + * with the old duty cycle and the new period. This is because the counters
>> + * may only be reloaded by first stopping them, or by letting them be
>> + * automatically reloaded at the end of a cycle. If this automatic reload
>> + * happens after we set TLR0 but before we set TLR1 then we will have a
>> + * bad cycle. This could probably be fixed by reading TCR0 just before
>> + * reprogramming, but I think it would add complexity for little gain.
>> + * - Cannot produce 100% duty cycle by configuring the TLRs. This might be
>> + * possible by stopping the counters at an appropriate point in the cycle,
>> + * but this is not (yet) implemented.
>> + * - Only produces "normal" output.
>> + * - Always produces low output if disabled.
>> + */
>> +
>> +#include <clocksource/timer-xilinx.h>
>> +#include <linux/clk.h>
>> +#include <linux/clk-provider.h>
>> +#include <linux/device.h>
>> +#include <linux/module.h>
>> +#include <linux/of.h>
>> +#include <linux/platform_device.h>
>> +#include <linux/pwm.h>
>> +#include <linux/regmap.h>
>> +
>> +/*
>> + * The following functions are "common" to drivers for this device, and may be
>> + * exported at a future date.
>> + */
>> +u32 xilinx_timer_tlr_cycles(struct xilinx_timer_priv *priv, u32 tcsr,
>> + u64 cycles)
>> +{
>> + WARN_ON(cycles < 2 || cycles - 2 > priv->max);
>> +
>> + if (tcsr & TCSR_UDT)
>> + return cycles - 2;
>> + return priv->max - cycles + 2;
>> +}
>> +
>> +unsigned int xilinx_timer_get_period(struct xilinx_timer_priv *priv,
>> + u32 tlr, u32 tcsr)
>> +{
>> + u64 cycles;
>> +
>> + if (tcsr & TCSR_UDT)
>> + cycles = tlr + 2;
>> + else
>> + cycles = (u64)priv->max - tlr + 2;
>> +
>> + /* cycles has a max of 2^32 + 2 */
>> + return DIV64_U64_ROUND_CLOSEST(cycles * NSEC_PER_SEC,
>> + clk_get_rate(priv->clk));
>
> Please round up here.

Please document the correct rounding mode you expect. The last time we
discussed this (3 months ago), you only said that rounding down was
incorrect...

>> +}
>> +
>> +/*
>> + * The idea here is to capture whether the PWM is actually running (e.g.
>> + * because we or the bootloader set it up) and we need to be careful to ensure
>> + * we don't cause a glitch. According to the data sheet, to enable the PWM we
>> + * need to
>> + *
>> + * - Set both timers to generate mode (MDT=1)
>> + * - Set both timers to PWM mode (PWMA=1)
>> + * - Enable the generate out signals (GENT=1)
>> + *
>> + * In addition,
>> + *
>> + * - The timer must be running (ENT=1)
>> + * - The timer must auto-reload TLR into TCR (ARHT=1)
>> + * - We must not be in the process of loading TLR into TCR (LOAD=0)
>> + * - Cascade mode must be disabled (CASC=0)
>> + *
>> + * If any of these differ from usual, then the PWM is either disabled, or is
>> + * running in a mode that this driver does not support.
>> + */
>> +#define TCSR_PWM_SET (TCSR_GENT | TCSR_ARHT | TCSR_ENT | TCSR_PWMA)
>> +#define TCSR_PWM_CLEAR (TCSR_MDT | TCSR_LOAD)
>> +#define TCSR_PWM_MASK (TCSR_PWM_SET | TCSR_PWM_CLEAR)
>> +
>> +struct xilinx_pwm_device {
>> + struct pwm_chip chip;
>> + struct xilinx_timer_priv priv;
>> +};
>> +
>> +static inline struct xilinx_timer_priv
>> +*xilinx_pwm_chip_to_priv(struct pwm_chip *chip)
>> +{
>> + return &container_of(chip, struct xilinx_pwm_device, chip)->priv;
>> +}
>> +
>> +static bool xilinx_timer_pwm_enabled(u32 tcsr0, u32 tcsr1)
>> +{
>> + return ((TCSR_PWM_MASK | TCSR_CASC) & tcsr0) == TCSR_PWM_SET &&
>> + (TCSR_PWM_MASK & tcsr1) == TCSR_PWM_SET;
>> +}
>> +
>> +static int xilinx_pwm_apply(struct pwm_chip *chip, struct pwm_device *unused,
>> + const struct pwm_state *state)
>> +{
>> + struct xilinx_timer_priv *priv = xilinx_pwm_chip_to_priv(chip);
>> + u32 tlr0, tlr1, tcsr0, tcsr1;
>> + u64 period_cycles, duty_cycles;
>> + unsigned long rate;
>> +
>> + if (state->polarity != PWM_POLARITY_NORMAL)
>> + return -EINVAL;
>> +
>> + /*
>> + * To be representable by TLR, cycles must be between 2 and
>> + * priv->max + 2. To enforce this we can reduce the duty
>> + * cycle, but we may not increase it.
>> + */
>> + rate = clk_get_rate(priv->clk);
>> + /* Prevent overflow by clamping to the worst case of rate */
>
> I wouldn't have called this "worst case of rate", maybe better use
> "maximal rate"?

OK

>> + period_cycles = min_t(u64, state->period, ULONG_MAX * NSEC_PER_SEC);
>> + period_cycles = mul_u64_u32_div(period_cycles, rate, NSEC_PER_SEC);
>> + if (period_cycles < 2 || period_cycles - 2 > priv->max)
>> + return -ERANGE;
>
> if period_cycles - 2 > priv->max the right reaction is to do
>
> period_cycles = priv->max + 2

It has been 5 months since we last talked about this, and yet you have
not submitted any patches for a "pwm_round_rate" function. Forgive me if
I am reticent to implement forward compatibility for an API which shows
no signs of appearing.

>> + duty_cycles = mul_u64_u32_div(state->duty_cycle, rate, NSEC_PER_SEC);
>
> duty_cycle needs sanitation in case period was reduced and duty_cycle is
> bigger now than period.

OK

>> + /*
>> + * If we specify 100% duty cycle, we will get 0% instead, so decrease
>> + * the duty cycle count by one.
>> + */
>> + if (period_cycles == duty_cycles)
>> + duty_cycles--;
>> +
>> + /* Round down to 0% duty cycle for unrepresentable duty cycles */
>> + if (duty_cycles < 2)
>> + duty_cycles = period_cycles;
>> +
>> + regmap_read(priv->map, TCSR0, &tcsr0);
>> + regmap_read(priv->map, TCSR1, &tcsr1);
>> + tlr0 = xilinx_timer_tlr_cycles(priv, tcsr0, period_cycles);
>> + tlr1 = xilinx_timer_tlr_cycles(priv, tcsr1, duty_cycles);
>> + regmap_write(priv->map, TLR0, tlr0);
>> + regmap_write(priv->map, TLR1, tlr1);
>> +
>> + if (state->enabled) {
>> + /*
>> + * If the PWM is already running, then the counters will be
>> + * reloaded at the end of the current cycle.
>> + */
>> + if (!xilinx_timer_pwm_enabled(tcsr0, tcsr1)) {
>> + /* Load TLR into TCR */
>> + regmap_write(priv->map, TCSR0, tcsr0 | TCSR_LOAD);
>> + regmap_write(priv->map, TCSR1, tcsr1 | TCSR_LOAD);
>> + /* Enable timers all at once with ENALL */
>> + tcsr0 = (TCSR_PWM_SET & ~TCSR_ENT) | (tcsr0 & TCSR_UDT);
>> + tcsr1 = TCSR_PWM_SET | TCSR_ENALL | (tcsr1 & TCSR_UDT);
>> + regmap_write(priv->map, TCSR0, tcsr0);
>> + regmap_write(priv->map, TCSR1, tcsr1);
>> + }
>> + } else {
>> + regmap_write(priv->map, TCSR0, 0);
>> + regmap_write(priv->map, TCSR1, 0);
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static void xilinx_pwm_get_state(struct pwm_chip *chip,
>> + struct pwm_device *unused,
>> + struct pwm_state *state)
>> +{
>> + struct xilinx_timer_priv *priv = xilinx_pwm_chip_to_priv(chip);
>> + u32 tlr0, tlr1, tcsr0, tcsr1;
>> +
>> + regmap_read(priv->map, TLR0, &tlr0);
>> + regmap_read(priv->map, TLR1, &tlr1);
>> + regmap_read(priv->map, TCSR0, &tcsr0);
>> + regmap_read(priv->map, TCSR1, &tcsr1);
>> + state->period = xilinx_timer_get_period(priv, tlr0, tcsr0);
>> + state->duty_cycle = xilinx_timer_get_period(priv, tlr1, tcsr1);
>> + state->enabled = xilinx_timer_pwm_enabled(tcsr0, tcsr1);
>> + state->polarity = PWM_POLARITY_NORMAL;
>> +
>> + /* 100% duty cycle results in constant low output */
>> + if (state->period == state->duty_cycle)
>> + state->duty_cycle = 0;
>> +}
>> +
>> +static const struct pwm_ops xilinx_pwm_ops = {
>> + .apply = xilinx_pwm_apply,
>> + .get_state = xilinx_pwm_get_state,
>> + .owner = THIS_MODULE,
>> +};
>> +
>> +static const struct regmap_config xilinx_pwm_regmap_config = {
>> + .reg_bits = 32,
>> + .reg_stride = 4,
>> + .val_bits = 32,
>> + .val_format_endian = REGMAP_ENDIAN_LITTLE,
>> + .max_register = TCR1,
>> +};
>> +
>> +static int xilinx_timer_probe(struct platform_device *pdev)
>> +{
>> + int ret;
>> + struct device *dev = &pdev->dev;
>> + struct device_node *np = dev->of_node;
>> + struct xilinx_timer_priv *priv;
>> + struct xilinx_pwm_device *pwm;
>
> The name "pwm" is usually reserved for struct pwm_device pointers. A
> typical name for this would be xlnxpwm or ddata.

I suppose. However, no variables of struct pwm_device are used in
this driver.

>> + u32 pwm_cells, one_timer, width;
>> + void __iomem *regs;
>> +
>> + ret = of_property_read_u32(np, "#pwm-cells", &pwm_cells);
>> + if (ret == -EINVAL)
>> + return -ENODEV;
>
> A comment about why this is done would be great.

OK. How about:

/* If there are no #pwm-cells, this binding is for a timer and not a PWM */

>> + if (ret)
>> + return dev_err_probe(dev, ret, "could not read #pwm-cells\n");
>> +
>> + pwm = devm_kzalloc(dev, sizeof(*pwm), GFP_KERNEL);
>> + if (!pwm)
>> + return -ENOMEM;
>> + platform_set_drvdata(pdev, pwm);
>> + priv = &pwm->priv;
>> +
>> + regs = devm_platform_ioremap_resource(pdev, 0);
>> + if (IS_ERR(regs))
>> + return PTR_ERR(regs);
>> +
>> + priv->map = devm_regmap_init_mmio(dev, regs,
>> + &xilinx_pwm_regmap_config);
>> + if (IS_ERR(priv->map))
>> + return dev_err_probe(dev, PTR_ERR(priv->map),
>> + "Could not create regmap\n");
>> +
>> + ret = of_property_read_u32(np, "xlnx,one-timer-only", &one_timer);
>> + if (ret)
>> + return dev_err_probe(dev, ret,
>> + "Could not read xlnx,one-timer-only\n");
>> +
>> + if (one_timer)
>> + return dev_err_probe(dev, -EINVAL,
>> + "Two timers required for PWM mode\n");
>> +
>> +
>> + ret = of_property_read_u32(np, "xlnx,count-width", &width);
>> + if (ret == -EINVAL)
>> + width = 32;
>> + else if (ret)
>> + return dev_err_probe(dev, ret,
>> + "Could not read xlnx,count-width\n");
>> +
>> + if (width != 8 && width != 16 && width != 32)
>> + return dev_err_probe(dev, -EINVAL,
>> + "Invalid counter width %d\n", width);
>> + priv->max = BIT_ULL(width) - 1;
>> +
>> + /*
>> + * The polarity of the generate outputs must be active high for PWM
>
> s/generate/generated/

The signals I am referring to are called "GenerateOut0" and
"GenerateOut1".

>> + * mode to work. We could determine this from the device tree, but
>> + * alas, such properties are not allowed to be used.
>> + */
>> +
>> + priv->clk = devm_clk_get(dev, "s_axi_aclk");
>> + if (IS_ERR(priv->clk))
>> + return dev_err_probe(dev, PTR_ERR(priv->clk),
>> + "Could not get clock\n");
>> +
>> + ret = clk_prepare_enable(priv->clk);
>> + if (ret)
>> + return dev_err_probe(dev, ret, "Clock enable failed\n");
>> + clk_rate_exclusive_get(priv->clk);
>> +
>> + pwm->chip.dev = dev;
>> + pwm->chip.ops = &xilinx_pwm_ops;
>> + pwm->chip.npwm = 1;
>> + ret = pwmchip_add(&pwm->chip);
>> + if (ret) {
>> + clk_rate_exclusive_put(priv->clk);
>> + clk_disable_unprepare(priv->clk);
>> + return dev_err_probe(dev, ret, "Could not register PWM chip\n");
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +static int xilinx_timer_remove(struct platform_device *pdev)
>> +{
>> + struct xilinx_pwm_device *pwm = platform_get_drvdata(pdev);
>> +
>> + pwmchip_remove(&pwm->chip);
>> + clk_rate_exclusive_put(pwm->priv.clk);
>> + clk_disable_unprepare(pwm->priv.clk);
>> + return 0;
>> +}
>> +
>> +static const struct of_device_id xilinx_timer_of_match[] = {
>> + { .compatible = "xlnx,xps-timer-1.00.a", },
>> + {},
>> +};
>> +MODULE_DEVICE_TABLE(of, xilinx_timer_of_match);
>> +
>> +static struct platform_driver xilinx_timer_driver = {
>> + .probe = xilinx_timer_probe,
>> + .remove = xilinx_timer_remove,
>> + .driver = {
>> + .name = "xilinx-timer",
>
> Doesn't this give a wrong impression as this is a PWM driver, not a
> timer driver?

Perhaps. Though this is the PWM driver for the Xilinx AXI timer, not the
Xilinx AXI PWM.

--Sean

>> + .of_match_table = of_match_ptr(xilinx_timer_of_match),
>> + },
>> +};
>> +module_platform_driver(xilinx_timer_driver);
>> +
>> +MODULE_ALIAS("platform:xilinx-timer");
>> +MODULE_DESCRIPTION("Xilinx LogiCORE IP AXI Timer driver");
>> +MODULE_LICENSE("GPL v2");
>> diff --git a/include/clocksource/timer-xilinx.h b/include/clocksource/timer-xilinx.h
>> new file mode 100644
>> index 000000000000..1f7757b84a5e
>> --- /dev/null
>> +++ b/include/clocksource/timer-xilinx.h
>> @@ -0,0 +1,91 @@
>> +/* SPDX-License-Identifier: GPL-2.0+ */
>> +/*
>> + * Copyright (C) 2021 Sean Anderson <sean.anderson@seco.com>
>> + */
>> +
>> +#ifndef XILINX_TIMER_H
>> +#define XILINX_TIMER_H
>> +
>> +#include <linux/compiler.h>
>> +
>> +#define TCSR0 0x00
>> +#define TLR0 0x04
>> +#define TCR0 0x08
>> +#define TCSR1 0x10
>> +#define TLR1 0x14
>> +#define TCR1 0x18
>> +
>> +#define TCSR_MDT BIT(0)
>> +#define TCSR_UDT BIT(1)
>> +#define TCSR_GENT BIT(2)
>> +#define TCSR_CAPT BIT(3)
>> +#define TCSR_ARHT BIT(4)
>> +#define TCSR_LOAD BIT(5)
>> +#define TCSR_ENIT BIT(6)
>> +#define TCSR_ENT BIT(7)
>> +#define TCSR_TINT BIT(8)
>> +#define TCSR_PWMA BIT(9)
>> +#define TCSR_ENALL BIT(10)
>> +#define TCSR_CASC BIT(11)
>> +
>> +struct clk;
>> +struct device_node;
>> +struct regmap;
>> +
>> +/**
>> + * struct xilinx_timer_priv - Private data for Xilinx AXI timer drivers
>> + * @map: Regmap of the device, possibly with an offset
>> + * @clk: Parent clock
>> + * @max: Maximum value of the counters
>> + */
>> +struct xilinx_timer_priv {
>> + struct regmap *map;
>> + struct clk *clk;
>> + u32 max;
>> +};
>> +
>> +/**
>> + * xilinx_timer_tlr_cycles() - Calculate the TLR for a period specified
>> + * in clock cycles
>> + * @priv: The timer's private data
>> + * @tcsr: The value of the TCSR register for this counter
>> + * @cycles: The number of cycles in this period
>> + *
>> + * Callers of this function MUST ensure that @cycles is representable as
>> + * a TLR.
>> + *
>> + * Return: The calculated value for TLR
>> + */
>> +u32 xilinx_timer_tlr_cycles(struct xilinx_timer_priv *priv, u32 tcsr,
>> + u64 cycles);
>> +
>> +/**
>> + * xilinx_timer_get_period() - Get the current period of a counter
>> + * @priv: The timer's private data
>> + * @tlr: The value of TLR for this counter
>> + * @tcsr: The value of TCSR for this counter
>> + *
>> + * Return: The period, in ns
>> + */
>> +unsigned int xilinx_timer_get_period(struct xilinx_timer_priv *priv,
>> + u32 tlr, u32 tcsr);
>> +
>> +/**
>> + * xilinx_timer_common_init() - Perform common initialization for Xilinx
>> + * AXI timer drivers.
>> + * @priv: The timer's private data
>> + * @np: The devicetree node for the timer
>> + * @one_timer: Set to %1 if there is only one timer
>> + *
>> + * This performs common initialization, such as detecting endianness,
>> + * and parsing devicetree properties. @priv->regs must be initialized
>> + * before calling this function. This function initializes @priv->read,
>> + * @priv->write, and @priv->width.
>> + *
>> + * Return: 0, or negative errno
>> + */
>> +int xilinx_timer_common_init(struct device_node *np,
>> + struct xilinx_timer_priv *priv,
>> + u32 *one_timer);
>> +
>> +#endif /* XILINX_TIMER_H */
>> --
>> 2.25.1
>>
>

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