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From:   Gregory CLEMENT <gregory.clement@bootlin.com>
To:     Pali =?utf-8?Q?Roh=C3=A1r?= <pali@kernel.org>,
        Michael Turquette <mturquette@baylibre.com>,
        Stephen Boyd <sboyd@kernel.org>,
        Rob Herring <robh+dt@kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc:     Andrew Lunn <andrew@lunn.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>,
        Vladimir Vid <vladimir.vid@sartura.hr>,
        Marek =?utf-8?Q?Beh=C3=BAn?= <kabel@kernel.org>,
        linux-clk@vger.kernel.org, linux-serial@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        devicetree@vger.kernel.org
Subject: Re: [PATCH v7 2/6] serial: mvebu-uart: implement UART clock driver
 for configuring UART base clock
In-Reply-To: <20210930095838.28145-3-pali@kernel.org>
References: <20210930095838.28145-1-pali@kernel.org>
 <20210930095838.28145-3-pali@kernel.org>
Date:   Wed, 13 Oct 2021 16:16:10 +0200
Message-ID: <87o87tdn85.fsf@BL-laptop>
MIME-Version: 1.0
Content-Type: text/plain; charset=utf-8
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Precedence: bulk

Hello Pali,

> This patch implements a new device driver for controlling UART clocks on
> Marvell Armada 3700 SoC. This device driver is loaded for devices which
> match compatible string "marvell,armada-3700-uart-clock".
>
> There are more pitfalls related to UART clocks. Both UARTs use same base
> clock source. Also divisors for TBG base clock are shared between both
> UARTs and are configured only from UART1 address space. Clocks can be
> enabled / disabled separately for UART1 and UART2, but they are controlled
> only from UART1 address space. Moreover Marvell Armada 3700 Functional
> Specifications has swapped bits for enabling/disabling UART1 and UART2
> clocks.
>
> So driver for controlling UART2 needs to have access to UART1 address space
> as UART1 address space contains some bits exclusively used by UART2 and
> also bits which are shared for both UART1 and UART2.
>
> For changing UART base clock (which controls both UARTs) during boot when
> UART driver is not ready and only early console is active, is not simple
> operation as it is required to also recalculate divisors to not change UART
> baudrate used by early console. So for this operation UART1 clock driver
> needs to access also into address space of UART2 where are registers for
> UART2 divisors.
>
> For these reasons, this new device driver for UART clocks does not use
> ioremap_resource(), but only ioremap() to prevent resource conflicts
> between UART clock driver and UART driver.
>
> Shared between drivers are only two 4-bytes registers: UART Clock Control
> and UART 2 Baud Rate Divisor. Access to these two registers are protected
> by one spinlock to prevent any conflicts. Access is required only during
> probe time, changing baudrate and during suspend/resume.
>
> Hardware can be configured to use one of following clocks as UART base
> clock: TBG-A-P, TBG-B-P, TBG-A-S, TBG-B-S, xtal. Not every clock is usable
> for higher buadrates. In DT node can be specified any subset and kernel
> choose the best one, which still supports required baudrate 9600. For
> smooth boot log output it is needed to specify clock used by early console
> otherwise garbage would be put on UART during probing for UART clock driver
> and transitioning from early console to normal console.
>
> This change is required to enable and configure TBG clock as a base clock
> for UART. TBG clock is required to achieve higher baudrates than
> 230400.

Did you have a review from the clock maintainer for this driver ?

I found it very unusual to have the implementation of a clok driver
inside an uart driver.

Gregory

>
> Signed-off-by: Pali Rohár <pali@kernel.org>
> ---
>  drivers/tty/serial/Kconfig      |   1 +
>  drivers/tty/serial/mvebu-uart.c | 519 +++++++++++++++++++++++++++++++-
>  2 files changed, 518 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> index 131a6a587acd..fe1a54231b19 100644
> --- a/drivers/tty/serial/Kconfig
> +++ b/drivers/tty/serial/Kconfig
> @@ -1444,6 +1444,7 @@ config SERIAL_STM32_CONSOLE
>  config SERIAL_MVEBU_UART
>  	bool "Marvell EBU serial port support"
>  	depends on ARCH_MVEBU || COMPILE_TEST
> +	depends on COMMON_CLK
>  	select SERIAL_CORE
>  	help
>  	  This driver is for Marvell EBU SoC's UART. If you have a machine
> diff --git a/drivers/tty/serial/mvebu-uart.c b/drivers/tty/serial/mvebu-uart.c
> index 231de29a6452..f3fb1f3718f2 100644
> --- a/drivers/tty/serial/mvebu-uart.c
> +++ b/drivers/tty/serial/mvebu-uart.c
> @@ -8,12 +8,14 @@
>  */
>  
>  #include <linux/clk.h>
> +#include <linux/clk-provider.h>
>  #include <linux/console.h>
>  #include <linux/delay.h>
>  #include <linux/device.h>
>  #include <linux/init.h>
>  #include <linux/io.h>
>  #include <linux/iopoll.h>
> +#include <linux/math64.h>
>  #include <linux/of.h>
>  #include <linux/of_address.h>
>  #include <linux/of_device.h>
> @@ -68,8 +70,31 @@
>  #define  STAT_BRK_ERR		(STAT_BRK_DET | STAT_FRM_ERR \
>  				 | STAT_PAR_ERR | STAT_OVR_ERR)
>  
> +/*
> + * Marvell Armada 3700 Functional Specifications describes that bit 21 of UART
> + * Clock Control register controls UART1 and bit 20 controls UART2. But in
> + * reality bit 21 controls UART2 and bit 20 controls UART1. This seems to be a
> + * bug in Marvell documentation. Hence following CLK_DIS macros are swapped.
> + */
> +
>  #define UART_BRDV		0x10
> +/* These bits are located in UART1 address space and control UART2 */
> +#define  UART2_CLK_DIS		BIT(21)
> +/* These bits are located in UART1 address space and control UART1 */
> +#define  UART1_CLK_DIS		BIT(20)
> +/* These bits are located in UART1 address space and control both UARTs */
> +#define  CLK_NO_XTAL		BIT(19)
> +#define  CLK_TBG_DIV1_SHIFT	15
> +#define  CLK_TBG_DIV1_MASK	0x7
> +#define  CLK_TBG_DIV1_MAX	6
> +#define  CLK_TBG_DIV2_SHIFT	12
> +#define  CLK_TBG_DIV2_MASK	0x7
> +#define  CLK_TBG_DIV2_MAX	6
> +#define  CLK_TBG_SEL_SHIFT	10
> +#define  CLK_TBG_SEL_MASK	0x3
> +/* These bits are located in both UARTs address space */
>  #define  BRDV_BAUD_MASK         0x3FF
> +#define  BRDV_BAUD_MAX		BRDV_BAUD_MASK
>  
>  #define UART_OSAMP		0x14
>  #define  OSAMP_DEFAULT_DIVISOR	16
> @@ -153,6 +178,8 @@ static struct mvebu_uart *to_mvuart(struct uart_port *port)
>  
>  static struct uart_port mvebu_uart_ports[MVEBU_NR_UARTS];
>  
> +static DEFINE_SPINLOCK(mvebu_uart_lock);
> +
>  /* Core UART Driver Operations */
>  static unsigned int mvebu_uart_tx_empty(struct uart_port *port)
>  {
> @@ -445,6 +472,7 @@ static void mvebu_uart_shutdown(struct uart_port *port)
>  static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
>  {
>  	unsigned int d_divisor, m_divisor;
> +	unsigned long flags;
>  	u32 brdv, osamp;
>  
>  	if (!port->uartclk)
> @@ -463,10 +491,12 @@ static int mvebu_uart_baud_rate_set(struct uart_port *port, unsigned int baud)
>  	m_divisor = OSAMP_DEFAULT_DIVISOR;
>  	d_divisor = DIV_ROUND_CLOSEST(port->uartclk, baud * m_divisor);
>  
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
>  	brdv = readl(port->membase + UART_BRDV);
>  	brdv &= ~BRDV_BAUD_MASK;
>  	brdv |= d_divisor;
>  	writel(brdv, port->membase + UART_BRDV);
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
>  
>  	osamp = readl(port->membase + UART_OSAMP);
>  	osamp &= ~OSAMP_DIVISORS_MASK;
> @@ -762,6 +792,7 @@ static int mvebu_uart_suspend(struct device *dev)
>  {
>  	struct mvebu_uart *mvuart = dev_get_drvdata(dev);
>  	struct uart_port *port = mvuart->port;
> +	unsigned long flags;
>  
>  	uart_suspend_port(&mvebu_uart_driver, port);
>  
> @@ -770,7 +801,9 @@ static int mvebu_uart_suspend(struct device *dev)
>  	mvuart->pm_regs.ctrl = readl(port->membase + UART_CTRL(port));
>  	mvuart->pm_regs.intr = readl(port->membase + UART_INTR(port));
>  	mvuart->pm_regs.stat = readl(port->membase + UART_STAT);
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
>  	mvuart->pm_regs.brdv = readl(port->membase + UART_BRDV);
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
>  	mvuart->pm_regs.osamp = readl(port->membase + UART_OSAMP);
>  
>  	device_set_wakeup_enable(dev, true);
> @@ -782,13 +815,16 @@ static int mvebu_uart_resume(struct device *dev)
>  {
>  	struct mvebu_uart *mvuart = dev_get_drvdata(dev);
>  	struct uart_port *port = mvuart->port;
> +	unsigned long flags;
>  
>  	writel(mvuart->pm_regs.rbr, port->membase + UART_RBR(port));
>  	writel(mvuart->pm_regs.tsh, port->membase + UART_TSH(port));
>  	writel(mvuart->pm_regs.ctrl, port->membase + UART_CTRL(port));
>  	writel(mvuart->pm_regs.intr, port->membase + UART_INTR(port));
>  	writel(mvuart->pm_regs.stat, port->membase + UART_STAT);
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
>  	writel(mvuart->pm_regs.brdv, port->membase + UART_BRDV);
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
>  	writel(mvuart->pm_regs.osamp, port->membase + UART_OSAMP);
>  
>  	uart_resume_port(&mvebu_uart_driver, port);
> @@ -972,6 +1008,476 @@ static struct platform_driver mvebu_uart_platform_driver = {
>  	},
>  };
>  
> +/* This code is based on clk-fixed-factor.c driver and modified. */
> +
> +struct mvebu_uart_clock {
> +	struct clk_hw clk_hw;
> +	int clock_idx;
> +	u32 pm_context_reg1;
> +	u32 pm_context_reg2;
> +};
> +
> +struct mvebu_uart_clock_base {
> +	struct mvebu_uart_clock clocks[2];
> +	unsigned int parent_rates[5];
> +	int parent_idx;
> +	unsigned int div;
> +	void __iomem *reg1;
> +	void __iomem *reg2;
> +	bool configured;
> +};
> +
> +#define PARENT_CLOCK_XTAL 4
> +
> +#define to_uart_clock(hw) container_of(hw, struct mvebu_uart_clock, clk_hw)
> +#define to_uart_clock_base(uart_clock) container_of(uart_clock, \
> +	struct mvebu_uart_clock_base, clocks[uart_clock->clock_idx])
> +
> +static int mvebu_uart_clock_prepare(struct clk_hw *hw)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +	unsigned int prev_clock_idx, prev_clock_rate, prev_d1d2;
> +	unsigned int parent_clock_idx, parent_clock_rate;
> +	unsigned long flags;
> +	unsigned int d1, d2;
> +	u64 divisor;
> +	u32 val;
> +
> +	/*
> +	 * This function just reconfigures UART Clock Control register (located
> +	 * in UART1 address space which controls both UART1 and UART2) to
> +	 * selected UART base clock and recalculate current UART1/UART2 divisors
> +	 * in their address spaces, so final baudrate will not be changed by
> +	 * switching UART base clock. This is required otherwise kernel boot log
> +	 * stops working. It is needed to ensure that UART baudrate does not
> +	 * change during this setup. It is one time operation, so based on
> +	 * "configured" member this function is skipped on second call. Because
> +	 * this UART Clock Control register (UART_BRDV) is shared between UART1
> +	 * baudrate function, UART1 clock selector and UART2 clock selector,
> +	 * every access to UART_BRDV (reg1) needs to be protected by lock.
> +	 */
> +
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
> +
> +	if (uart_clock_base->configured) {
> +		spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> +		return 0;
> +	}
> +
> +	parent_clock_idx = uart_clock_base->parent_idx;
> +	parent_clock_rate = uart_clock_base->parent_rates[parent_clock_idx];
> +
> +	val = readl(uart_clock_base->reg1);
> +
> +	if (uart_clock_base->div > CLK_TBG_DIV1_MAX) {
> +		d1 = CLK_TBG_DIV1_MAX;
> +		d2 = uart_clock_base->div / CLK_TBG_DIV1_MAX;
> +	} else {
> +		d1 = uart_clock_base->div;
> +		d2 = 1;
> +	}
> +
> +	if (val & CLK_NO_XTAL) {
> +		prev_clock_idx = (val >> CLK_TBG_SEL_SHIFT) & CLK_TBG_SEL_MASK;
> +		prev_d1d2 = ((val >> CLK_TBG_DIV1_SHIFT) & CLK_TBG_DIV1_MASK)
> +			  * ((val >> CLK_TBG_DIV2_SHIFT) & CLK_TBG_DIV2_MASK);
> +	} else {
> +		prev_clock_idx = PARENT_CLOCK_XTAL;
> +		prev_d1d2 = 1;
> +	}
> +
> +	/* Note that uart_clock_base->parent_rates[i] may not be available */
> +	prev_clock_rate = uart_clock_base->parent_rates[prev_clock_idx];
> +
> +	/* Recalculate UART1 divisor so UART1 baudrate does not change */
> +	if (prev_clock_rate) {
> +		divisor = DIV_U64_ROUND_CLOSEST((u64)(val & BRDV_BAUD_MASK) *
> +						parent_clock_rate * prev_d1d2,
> +						prev_clock_rate * d1 * d2);
> +		if (divisor < 1)
> +			divisor = 1;
> +		else if (divisor > BRDV_BAUD_MAX)
> +			divisor = BRDV_BAUD_MAX;
> +		val = (val & ~BRDV_BAUD_MASK) | divisor;
> +	}
> +
> +	if (parent_clock_idx != PARENT_CLOCK_XTAL) {
> +		/* Do not use XTAL, select TBG clock and TBG d1 * d2 divisors */
> +		val |= CLK_NO_XTAL;
> +		val &= ~(CLK_TBG_DIV1_MASK << CLK_TBG_DIV1_SHIFT);
> +		val |= d1 << CLK_TBG_DIV1_SHIFT;
> +		val &= ~(CLK_TBG_DIV2_MASK << CLK_TBG_DIV2_SHIFT);
> +		val |= d2 << CLK_TBG_DIV2_SHIFT;
> +		val &= ~(CLK_TBG_SEL_MASK << CLK_TBG_SEL_SHIFT);
> +		val |= parent_clock_idx << CLK_TBG_SEL_SHIFT;
> +	} else {
> +		/* Use XTAL, TBG bits are then ignored */
> +		val &= ~CLK_NO_XTAL;
> +	}
> +
> +	writel(val, uart_clock_base->reg1);
> +
> +	/* Recalculate UART2 divisor so UART2 baudrate does not change */
> +	if (prev_clock_rate) {
> +		val = readl(uart_clock_base->reg2);
> +		divisor = DIV_U64_ROUND_CLOSEST((u64)(val & BRDV_BAUD_MASK) *
> +						parent_clock_rate * prev_d1d2,
> +						prev_clock_rate * d1 * d2);
> +		if (divisor < 1)
> +			divisor = 1;
> +		else if (divisor > BRDV_BAUD_MAX)
> +			divisor = BRDV_BAUD_MAX;
> +		val = (val & ~BRDV_BAUD_MASK) | divisor;
> +		writel(val, uart_clock_base->reg2);
> +	}
> +
> +	uart_clock_base->configured = true;
> +
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> +
> +	return 0;
> +}
> +
> +static int mvebu_uart_clock_enable(struct clk_hw *hw)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +	unsigned long flags;
> +	u32 val;
> +
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
> +
> +	val = readl(uart_clock_base->reg1);
> +
> +	if (uart_clock->clock_idx == 0)
> +		val &= ~UART1_CLK_DIS;
> +	else
> +		val &= ~UART2_CLK_DIS;
> +
> +	writel(val, uart_clock_base->reg1);
> +
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> +
> +	return 0;
> +}
> +
> +static void mvebu_uart_clock_disable(struct clk_hw *hw)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +	unsigned long flags;
> +	u32 val;
> +
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
> +
> +	val = readl(uart_clock_base->reg1);
> +
> +	if (uart_clock->clock_idx == 0)
> +		val |= UART1_CLK_DIS;
> +	else
> +		val |= UART2_CLK_DIS;
> +
> +	writel(val, uart_clock_base->reg1);
> +
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> +}
> +
> +static int mvebu_uart_clock_is_enabled(struct clk_hw *hw)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +	u32 val;
> +
> +	val = readl(uart_clock_base->reg1);
> +
> +	if (uart_clock->clock_idx == 0)
> +		return !(val & UART1_CLK_DIS);
> +	else
> +		return !(val & UART2_CLK_DIS);
> +}
> +
> +static int mvebu_uart_clock_save_context(struct clk_hw *hw)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
> +	uart_clock->pm_context_reg1 = readl(uart_clock_base->reg1);
> +	uart_clock->pm_context_reg2 = readl(uart_clock_base->reg2);
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> +
> +	return 0;
> +}
> +
> +static void mvebu_uart_clock_restore_context(struct clk_hw *hw)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&mvebu_uart_lock, flags);
> +	writel(uart_clock->pm_context_reg1, uart_clock_base->reg1);
> +	writel(uart_clock->pm_context_reg2, uart_clock_base->reg2);
> +	spin_unlock_irqrestore(&mvebu_uart_lock, flags);
> +}
> +
> +static unsigned long mvebu_uart_clock_recalc_rate(struct clk_hw *hw,
> +						  unsigned long parent_rate)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +
> +	return parent_rate / uart_clock_base->div;
> +}
> +
> +static long mvebu_uart_clock_round_rate(struct clk_hw *hw, unsigned long rate,
> +					unsigned long *parent_rate)
> +{
> +	struct mvebu_uart_clock *uart_clock = to_uart_clock(hw);
> +	struct mvebu_uart_clock_base *uart_clock_base =
> +						to_uart_clock_base(uart_clock);
> +
> +	return *parent_rate / uart_clock_base->div;
> +}
> +
> +static int mvebu_uart_clock_set_rate(struct clk_hw *hw, unsigned long rate,
> +				     unsigned long parent_rate)
> +{
> +	/*
> +	 * We must report success but we can do so unconditionally because
> +	 * mvebu_uart_clock_round_rate returns values that ensure this call is a
> +	 * nop.
> +	 */
> +
> +	return 0;
> +}
> +
> +static const struct clk_ops mvebu_uart_clock_ops = {
> +	.prepare = mvebu_uart_clock_prepare,
> +	.enable = mvebu_uart_clock_enable,
> +	.disable = mvebu_uart_clock_disable,
> +	.is_enabled = mvebu_uart_clock_is_enabled,
> +	.save_context = mvebu_uart_clock_save_context,
> +	.restore_context = mvebu_uart_clock_restore_context,
> +	.round_rate = mvebu_uart_clock_round_rate,
> +	.set_rate = mvebu_uart_clock_set_rate,
> +	.recalc_rate = mvebu_uart_clock_recalc_rate,
> +};
> +
> +static int mvebu_uart_clock_register(struct device *dev,
> +				     struct mvebu_uart_clock *uart_clock,
> +				     const char *name,
> +				     const char *parent_name)
> +{
> +	struct clk_init_data init = { };
> +
> +	uart_clock->clk_hw.init = &init;
> +
> +	init.name = name;
> +	init.ops = &mvebu_uart_clock_ops;
> +	init.flags = 0;
> +	init.num_parents = 1;
> +	init.parent_names = &parent_name;
> +
> +	return devm_clk_hw_register(dev, &uart_clock->clk_hw);
> +}
> +
> +static int mvebu_uart_clock_probe(struct platform_device *pdev)
> +{
> +	static const char *const uart_clk_names[] = { "uart_1", "uart_2" };
> +	static const char *const parent_clk_names[] = { "TBG-A-P", "TBG-B-P",
> +							"TBG-A-S", "TBG-B-S",
> +							"xtal" };
> +	struct clk *parent_clks[ARRAY_SIZE(parent_clk_names)];
> +	struct mvebu_uart_clock_base *uart_clock_base;
> +	struct clk_hw_onecell_data *hw_clk_data;
> +	struct device *dev = &pdev->dev;
> +	int i, parent_clk_idx, ret;
> +	unsigned long div, rate;
> +	struct resource *res;
> +	unsigned int d1, d2;
> +
> +	BUILD_BUG_ON(ARRAY_SIZE(uart_clk_names) !=
> +		     ARRAY_SIZE(uart_clock_base->clocks));
> +	BUILD_BUG_ON(ARRAY_SIZE(parent_clk_names) !=
> +		     ARRAY_SIZE(uart_clock_base->parent_rates));
> +
> +	uart_clock_base = devm_kzalloc(dev,
> +				       sizeof(*uart_clock_base),
> +				       GFP_KERNEL);
> +	if (!uart_clock_base)
> +		return -ENOMEM;
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	if (!res) {
> +		dev_err(dev, "Couldn't get first register\n");
> +		return -ENOENT;
> +	}
> +
> +	/*
> +	 * UART Clock Control register (reg1 / UART_BRDV) is in address range
> +	 * of UART1 (standard UART variant), controls clock source and dividers
> +	 * for both UART1 and UART2 and is supplied via DT as first resource.
> +	 * Therefore use ioremap() function rather than ioremap_resource() to
> +	 * avoid conflicts with UART1 driver. Access to UART_BRDV is protected
> +	 * by lock shared between clock and UART driver.
> +	 */
> +	uart_clock_base->reg1 = devm_ioremap(dev, res->start,
> +					     resource_size(res));
> +	if (IS_ERR(uart_clock_base->reg1))
> +		return PTR_ERR(uart_clock_base->reg1);
> +
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 1);
> +	if (!res) {
> +		dev_err(dev, "Couldn't get second register\n");
> +		return -ENOENT;
> +	}
> +
> +	/*
> +	 * UART 2 Baud Rate Divisor register (reg2 / UART_BRDV) is in address
> +	 * range of UART2 (extended UART variant), controls only one UART2
> +	 * specific divider and is supplied via DT as second resource.
> +	 * Therefore use ioremap() function rather than ioremap_resource() to
> +	 * avoid conflicts with UART2 driver. Access to UART_BRDV is protected
> +	 * by lock shared between clock and UART driver.
> +	 */
> +	uart_clock_base->reg2 = devm_ioremap(dev, res->start,
> +					     resource_size(res));
> +	if (IS_ERR(uart_clock_base->reg2))
> +		return PTR_ERR(uart_clock_base->reg2);
> +
> +	hw_clk_data = devm_kzalloc(dev,
> +				   struct_size(hw_clk_data, hws,
> +					       ARRAY_SIZE(uart_clk_names)),
> +				   GFP_KERNEL);
> +	if (!hw_clk_data)
> +		return -ENOMEM;
> +
> +	hw_clk_data->num = ARRAY_SIZE(uart_clk_names);
> +	for (i = 0; i < ARRAY_SIZE(uart_clk_names); i++) {
> +		hw_clk_data->hws[i] = &uart_clock_base->clocks[i].clk_hw;
> +		uart_clock_base->clocks[i].clock_idx = i;
> +	}
> +
> +	parent_clk_idx = -1;
> +
> +	for (i = 0; i < ARRAY_SIZE(parent_clk_names); i++) {
> +		parent_clks[i] = devm_clk_get(dev, parent_clk_names[i]);
> +		if (IS_ERR(parent_clks[i])) {
> +			if (PTR_ERR(parent_clks[i]) == -EPROBE_DEFER)
> +				return -EPROBE_DEFER;
> +			dev_warn(dev, "Couldn't get the parent clock %s: %ld\n",
> +				parent_clk_names[i], PTR_ERR(parent_clks[i]));
> +			continue;
> +		}
> +
> +		ret = clk_prepare_enable(parent_clks[i]);
> +		if (ret) {
> +			dev_warn(dev, "Couldn't enable parent clock %s: %d\n",
> +				parent_clk_names[i], ret);
> +			continue;
> +		}
> +		rate = clk_get_rate(parent_clks[i]);
> +		uart_clock_base->parent_rates[i] = rate;
> +
> +		if (i != PARENT_CLOCK_XTAL) {
> +			/*
> +			 * Calculate the smallest TBG d1 and d2 divisors that
> +			 * still can provide 9600 baudrate.
> +			 */
> +			d1 = DIV_ROUND_UP(rate, 9600 * OSAMP_DEFAULT_DIVISOR *
> +						BRDV_BAUD_MAX);
> +			if (d1 < 1)
> +				d1 = 1;
> +			else if (d1 > CLK_TBG_DIV1_MAX)
> +				d1 = CLK_TBG_DIV1_MAX;
> +
> +			d2 = DIV_ROUND_UP(rate, 9600 * OSAMP_DEFAULT_DIVISOR *
> +						BRDV_BAUD_MAX * d1);
> +			if (d2 < 1)
> +				d2 = 1;
> +			else if (d2 > CLK_TBG_DIV2_MAX)
> +				d2 = CLK_TBG_DIV2_MAX;
> +		} else {
> +			/*
> +			 * When UART clock uses XTAL clock as a source then it
> +			 * is not possible to use d1 and d2 divisors.
> +			 */
> +			d1 = d2 = 1;
> +		}
> +
> +		/* Skip clock source which cannot provide 9600 baudrate */
> +		if (rate > 9600 * OSAMP_DEFAULT_DIVISOR * BRDV_BAUD_MAX * d1 * d2)
> +			continue;
> +
> +		/*
> +		 * Choose TBG clock source with the smallest divisors. Use XTAL
> +		 * clock source only in case TBG is not available as XTAL cannot
> +		 * be used for baudrates higher than 230400.
> +		 */
> +		if (parent_clk_idx == -1 ||
> +		    (i != PARENT_CLOCK_XTAL && div > d1 * d2)) {
> +			parent_clk_idx = i;
> +			div = d1 * d2;
> +		}
> +	}
> +
> +	for (i = 0; i < ARRAY_SIZE(parent_clk_names); i++) {
> +		if (i == parent_clk_idx || IS_ERR(parent_clks[i]))
> +			continue;
> +		clk_disable_unprepare(parent_clks[i]);
> +		devm_clk_put(dev, parent_clks[i]);
> +	}
> +
> +	if (parent_clk_idx == -1) {
> +		dev_err(dev, "No usable parent clock\n");
> +		return -ENOENT;
> +	}
> +
> +	uart_clock_base->parent_idx = parent_clk_idx;
> +	uart_clock_base->div = div;
> +
> +	dev_notice(dev, "Using parent clock %s as base UART clock\n",
> +		   __clk_get_name(parent_clks[parent_clk_idx]));
> +
> +	for (i = 0; i < ARRAY_SIZE(uart_clk_names); i++) {
> +		ret = mvebu_uart_clock_register(dev,
> +				&uart_clock_base->clocks[i],
> +				uart_clk_names[i],
> +				__clk_get_name(parent_clks[parent_clk_idx]));
> +		if (ret) {
> +			dev_err(dev, "Can't register UART clock %d: %d\n",
> +				i, ret);
> +			return ret;
> +		}
> +	}
> +
> +	return devm_of_clk_add_hw_provider(dev, of_clk_hw_onecell_get,
> +					   hw_clk_data);
> +}
> +
> +static const struct of_device_id mvebu_uart_clock_of_match[] = {
> +	{ .compatible = "marvell,armada-3700-uart-clock", },
> +	{ }
> +};
> +
> +static struct platform_driver mvebu_uart_clock_platform_driver = {
> +	.probe = mvebu_uart_clock_probe,
> +	.driver		= {
> +		.name	= "mvebu-uart-clock",
> +		.of_match_table = mvebu_uart_clock_of_match,
> +	},
> +};
> +
>  static int __init mvebu_uart_init(void)
>  {
>  	int ret;
> @@ -980,10 +1486,19 @@ static int __init mvebu_uart_init(void)
>  	if (ret)
>  		return ret;
>  
> +	ret = platform_driver_register(&mvebu_uart_clock_platform_driver);
> +	if (ret) {
> +		uart_unregister_driver(&mvebu_uart_driver);
> +		return ret;
> +	}
> +
>  	ret = platform_driver_register(&mvebu_uart_platform_driver);
> -	if (ret)
> +	if (ret) {
> +		platform_driver_unregister(&mvebu_uart_clock_platform_driver);
>  		uart_unregister_driver(&mvebu_uart_driver);
> +		return ret;
> +	}
>  
> -	return ret;
> +	return 0;
>  }
>  arch_initcall(mvebu_uart_init);
> -- 
> 2.20.1
>

-- 
Gregory Clement, Bootlin
Embedded Linux and Kernel engineering
http://bootlin.com