Re: [PATCH v4 04/10] serial: bflb_uart: add Bouffalolab UART Driver

From: Jisheng Zhang <jszhang@kernel.org>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Thomas Gleixner <tglx@linutronix.de>,
	Marc Zyngier <maz@kernel.org>, Rob Herring <robh+dt@kernel.org>,
	Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
	Conor Dooley <conor+dt@kernel.org>,
	Palmer Dabbelt <palmer@dabbelt.com>,
	Paul Walmsley <paul.walmsley@sifive.com>,
	Albert Ou <aou@eecs.berkeley.edu>,
	Jiri Slaby <jirislaby@kernel.org>,
	linux-kernel@vger.kernel.org, linux-riscv@lists.infradead.org,
	devicetree@vger.kernel.org, linux-serial@vger.kernel.org
Subject: Re: [PATCH v4 04/10] serial: bflb_uart: add Bouffalolab UART Driver
Date: Wed, 31 May 2023 22:09:56 +0800	[thread overview]
Message-ID: <ZHdVNIQpgfCzimRg@xhacker> (raw)
In-Reply-To: <2023053010-gondola-luminous-f5e7@gregkh>

On Tue, May 30, 2023 at 11:36:00AM +0100, Greg Kroah-Hartman wrote:
> On Thu, May 18, 2023 at 11:22:38PM +0800, Jisheng Zhang wrote:
> > Add the driver for Bouffalolab UART IP which is found in Bouffalolab
> > SoCs such as bl808.
> 
> New uarts are being created that are NOT 8250-like?  Why????

Hi,

I'm not sure I understand your meaning. I guess you mean writing the new
uart driver following 8250 style. And the latest example is
sunplus-uart.c, it can be used as an example how to write a 8250 style
driver for new non-8250 uart IP. 

If the above guesses are wrong, could you please provide more details?

Thanks

> 
> 
> > 
> > UART driver probe will create path named "/dev/ttySx".
> > 
> > Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
> > ---
> >  drivers/tty/serial/Kconfig       |  18 +
> >  drivers/tty/serial/Makefile      |   1 +
> >  drivers/tty/serial/bflb_uart.c   | 586 +++++++++++++++++++++++++++++++
> >  include/uapi/linux/serial_core.h |   3 +
> >  4 files changed, 608 insertions(+)
> >  create mode 100644 drivers/tty/serial/bflb_uart.c
> > 
> > diff --git a/drivers/tty/serial/Kconfig b/drivers/tty/serial/Kconfig
> > index 398e5aac2e77..abc30a0713f5 100644
> > --- a/drivers/tty/serial/Kconfig
> > +++ b/drivers/tty/serial/Kconfig
> > @@ -179,6 +179,24 @@ config SERIAL_ATMEL_TTYAT
> >  
> >  	  Say Y if you have an external 8250/16C550 UART.  If unsure, say N.
> >  
> > +config SERIAL_BFLB
> > +	tristate "Bouffalolab serial port support"
> > +	select SERIAL_CORE
> > +	depends on COMMON_CLK
> > +	help
> > +	  This enables the driver for the Bouffalolab's serial.
> > +
> > +config SERIAL_BFLB_CONSOLE
> > +	bool "Support for console on Bouffalolab serial port"
> > +	depends on SERIAL_BFLB=y
> > +	select SERIAL_CORE_CONSOLE
> > +	select SERIAL_EARLYCON
> > +	help
> > +	  Say Y here if you wish to use a Bouffalolab UART as the
> > +	  system console (the system console is the device which
> > +	  receives all kernel messages and warnings and which allows
> > +	  logins in single user mode) as /dev/ttySn.
> > +
> >  config SERIAL_KGDB_NMI
> >  	bool "Serial console over KGDB NMI debugger port"
> >  	depends on KGDB_SERIAL_CONSOLE
> > diff --git a/drivers/tty/serial/Makefile b/drivers/tty/serial/Makefile
> > index cd9afd9e3018..5788a708d327 100644
> > --- a/drivers/tty/serial/Makefile
> > +++ b/drivers/tty/serial/Makefile
> > @@ -25,6 +25,7 @@ obj-$(CONFIG_SERIAL_8250) += 8250/
> >  
> >  obj-$(CONFIG_SERIAL_AMBA_PL010) += amba-pl010.o
> >  obj-$(CONFIG_SERIAL_AMBA_PL011) += amba-pl011.o
> > +obj-$(CONFIG_SERIAL_BFLB) += bflb_uart.o
> >  obj-$(CONFIG_SERIAL_CLPS711X) += clps711x.o
> >  obj-$(CONFIG_SERIAL_PXA_NON8250) += pxa.o
> >  obj-$(CONFIG_SERIAL_SA1100) += sa1100.o
> > diff --git a/drivers/tty/serial/bflb_uart.c b/drivers/tty/serial/bflb_uart.c
> > new file mode 100644
> > index 000000000000..3f80bba8599a
> > --- /dev/null
> > +++ b/drivers/tty/serial/bflb_uart.c
> > @@ -0,0 +1,586 @@
> > +// SPDX-License-Identifier: GPL-2.0+
> > +/*
> > + * Based on bflb_uart.c, by Bouffalolab team
> > + *
> > + * Copyright (C) 2022 Jisheng Zhang <jszhang@kernel.org>
> 
> It is 2023 :)
> 
> > + */
> > +
> > +#include <linux/bitfield.h>
> > +#include <linux/clk.h>
> > +#include <linux/console.h>
> > +#include <linux/kernel.h>
> > +#include <linux/init.h>
> > +#include <linux/interrupt.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/serial.h>
> > +#include <linux/serial_core.h>
> > +#include <linux/tty.h>
> > +#include <linux/tty_flip.h>
> > +
> > +#define UART_UTX_CONFIG			0x00
> > +#define  UART_CR_UTX_EN			BIT(0)
> > +#define  UART_CR_UTX_CTS_EN		BIT(1)
> > +#define  UART_CR_UTX_FRM_EN		BIT(2)
> > +#define  UART_CR_UTX_PRT_EN		BIT(4)
> > +#define  UART_CR_UTX_PRT_SEL		BIT(5)
> > +#define  UART_CR_UTX_BIT_CNT_D_MSK	GENMASK(10, 8)
> > +#define  UART_CR_UTX_BIT_CNT_P_MSK	GENMASK(12, 11)
> > +#define UART_URX_CONFIG			0x04
> > +#define  UART_CR_URX_EN			BIT(0)
> > +#define  UART_CR_URX_PRT_EN		BIT(4)
> > +#define  UART_CR_URX_PRT_SEL		BIT(5)
> > +#define  UART_CR_URX_BIT_CNT_D_MSK	GENMASK(10, 8)
> > +#define UART_BIT_PRD			0x08
> > +#define  UART_CR_UTX_BIT_PRD_MSK	GENMASK(15, 0)
> > +#define  UART_CR_URX_BIT_PRD_MSK	GENMASK(31, 16)
> > +#define UART_DATA_CONFIG		0x0c
> > +#define  UART_CR_UART_BIT_INV		BIT(0)
> > +#define UART_URX_RTO_TIMER		0x18
> > +#define  UART_CR_URX_RTO_VALUE_MSK	GENMASK(7, 0)
> > +#define UART_SW_MODE			0x1c
> > +#define UART_INT_STS			0x20
> > +#define  UART_UTX_END_INT		BIT(0)
> > +#define  UART_URX_END_INT		BIT(1)
> > +#define  UART_UTX_FIFO_INT		BIT(2)
> > +#define  UART_URX_FIFO_INT		BIT(3)
> > +#define  UART_URX_RTO_INT		BIT(4)
> > +#define  UART_URX_PCE_INT		BIT(5)
> > +#define  UART_UTX_FER_INT		BIT(6)
> > +#define  UART_URX_FER_INT		BIT(7)
> > +#define  UART_URX_LSE_INT		BIT(8)
> > +#define UART_INT_MASK			0x24
> > +#define UART_INT_CLEAR			0x28
> > +#define UART_INT_EN			0x2c
> > +#define UART_STATUS			0x30
> > +#define  UART_STS_UTX_BUS_BUSY		BIT(0)
> > +#define UART_FIFO_CONFIG_0		0x80
> > +#define  UART_DMA_TX_EN			BIT(0)
> > +#define  UART_DMA_RX_EN			BIT(1)
> > +#define  UART_TX_FIFO_CLR		BIT(2)
> > +#define  UART_RX_FIFO_CLR		BIT(3)
> > +#define  UART_TX_FIFO_OVERFLOW		BIT(4)
> > +#define  UART_TX_FIFO_UNDERFLOW		BIT(5)
> > +#define  UART_RX_FIFO_OVERFLOW		BIT(6)
> > +#define  UART_RX_FIFO_UNDERFLOW		BIT(7)
> > +#define UART_FIFO_CONFIG_1		0x84
> > +#define  UART_TX_FIFO_CNT_MSK		GENMASK(5, 0)
> > +#define  UART_RX_FIFO_CNT_MSK		GENMASK(13, 8)
> > +#define  UART_TX_FIFO_TH_MSK		GENMASK(20, 16)
> > +#define  UART_RX_FIFO_TH_MSK		GENMASK(28, 24)
> > +#define UART_FIFO_WDATA			0x88
> > +#define UART_FIFO_RDATA			0x8c
> > +#define  UART_FIFO_RDATA_MSK		GENMASK(7, 0)
> > +
> > +#define BFLB_UART_MAXPORTS		8
> > +#define BFLB_UART_BAUD			2000000
> > +#define BFLB_UART_RX_FIFO_TH		7
> > +#define BFLB_UART_TX_FIFO_TH		15
> > +#define BFLB_UART_URX_RTO_TIME		0x4f
> > +
> > +struct bflb_uart_port {
> > +	struct uart_port port;
> > +	struct clk *clk;
> > +};
> > +
> > +static struct bflb_uart_port *bflb_uart_ports[BFLB_UART_MAXPORTS];
> > +
> > +static inline u32 rdl(struct uart_port *port, u32 reg)
> > +{
> > +	return readl_relaxed(port->membase + reg);
> > +}
> > +
> > +static inline void wrl(struct uart_port *port, u32 reg, u32 value)
> > +{
> > +	writel_relaxed(value, port->membase + reg);
> > +}
> > +
> > +static inline void wrb(struct uart_port *port, u32 reg, u8 value)
> > +{
> > +	writeb_relaxed(value, port->membase + reg);
> > +}
> > +
> > +static unsigned int bflb_uart_tx_empty(struct uart_port *port)
> > +{
> > +	return (rdl(port, UART_FIFO_CONFIG_1) & UART_TX_FIFO_CNT_MSK) ? TIOCSER_TEMT : 0;
> > +}
> > +
> > +static unsigned int bflb_uart_get_mctrl(struct uart_port *port)
> > +{
> > +	return TIOCM_CAR | TIOCM_DSR | TIOCM_CTS;
> > +}
> > +
> > +static void bflb_uart_set_mctrl(struct uart_port *port, unsigned int sigs)
> > +{
> > +}
> 
> Why is a blank function required here?
> 
> 
> > --- a/include/uapi/linux/serial_core.h
> > +++ b/include/uapi/linux/serial_core.h
> > @@ -279,4 +279,7 @@
> >  /* Sunplus UART */
> >  #define PORT_SUNPLUS	123
> >  
> > +/* Bouffalolab UART */
> > +#define PORT_BFLB	124
> 
> Why is this required?  What userspace code is going to need this?
> 
> thanks,
> 
> greg k-h

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