[U-Boot] [PATCH v3 06/14] drivers: serial: add driver for Microchip PIC32 UART controller.

[Purna Chandra Mandal <purna.mandal@microchip.com>]

On 01/14/2016 01:39 AM, Simon Glass wrote:

> Hi Purna,
>
> On 12 January 2016 at 03:18, Purna Chandra Mandal
> <purna.mandal@microchip.com> wrote:
>> From: Paul Thacker <paul.thacker@microchip.com>
>>
>> This adds PIC32 UART controller support based on driver model.
>>
>> Signed-off-by: Paul Thacker <paul.thacker@microchip.com>
>> Signed-off-by: Purna Chandra Mandal <purna.mandal@microchip.com>
>>
>>
>> ---
>>
>> Changes in v3:
>> - remove ofdata_to_platdata, and replace platdata with priv
>> - remove special handling of '\r' as being handled by serial-uclass
>> - remove loop to wait for space in tx buffer before pumping char
>>
>> Changes in v2:
>> - fix missing/corrupted chars during baud rate change
>> - remove loop until any char is avaialbale in getc()
>>
>>  .../serial/microchip,pic32-uart.txt                |   5 +
>>  drivers/serial/Kconfig                             |  13 ++
>>  drivers/serial/Makefile                            |   1 +
>>  drivers/serial/serial_pic32.c                      | 199 +++++++++++++++++++++
>>  4 files changed, 218 insertions(+)
>>  create mode 100644 doc/device-tree-bindings/serial/microchip,pic32-uart.txt
>>  create mode 100644 drivers/serial/serial_pic32.c
>>
> Reviewed-by: Simon Glass <sjg@chromium.org>
>
> One nit/question below.
>
>> diff --git a/doc/device-tree-bindings/serial/microchip,pic32-uart.txt b/doc/device-tree-bindings/serial/microchip,pic32-uart.txt
>> new file mode 100644
>> index 0000000..f00e215
>> --- /dev/null
>> +++ b/doc/device-tree-bindings/serial/microchip,pic32-uart.txt
>> @@ -0,0 +1,5 @@
>> +* Microchip PIC32 serial UART
>> +
>> +Required properties:
>> +- compatible: must be "microchip,pic32mzda-uart".
>> +- reg: exactly one register range.
>> diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
>> index 1fc287e..9763ea1 100644
>> --- a/drivers/serial/Kconfig
>> +++ b/drivers/serial/Kconfig
>> @@ -107,6 +107,14 @@ config DEBUG_UART_APBUART
>>           will need to provide parameters to make this work. The driver will
>>           be available until the real driver model serial is running.
>>
>> +config DEBUG_UART_PIC32
>> +       bool "Microchip PIC32"
>> +       help
>> +         Select this to enable a debug UART using the serial_pic32 driver. You
>> +         will need to provide parameters to make this work. The driver will
>> +         be available until the real driver model serial is running.
>> +
>> +
>>  endchoice
>>
>>  config DEBUG_UART_BASE
>> @@ -223,4 +231,9 @@ config UNIPHIER_SERIAL
>>           If you have a UniPhier based board and want to use the on-chip
>>           serial ports, say Y to this option. If unsure, say N.
>>
>> +config PIC32_SERIAL
>> +       bool "Support for Microchip PIC32 on-chip UART"
>> +       help
>> +         Support for the UART found on Microchip PIC32 SoC's.
>> +
>>  endmenu
>> diff --git a/drivers/serial/Makefile b/drivers/serial/Makefile
>> index dd87147..57cd38b 100644
>> --- a/drivers/serial/Makefile
>> +++ b/drivers/serial/Makefile
>> @@ -41,6 +41,7 @@ obj-$(CONFIG_MXS_AUART) += mxs_auart.o
>>  obj-$(CONFIG_ARC_SERIAL) += serial_arc.o
>>  obj-$(CONFIG_UNIPHIER_SERIAL) += serial_uniphier.o
>>  obj-$(CONFIG_STM32_SERIAL) += serial_stm32.o
>> +obj-$(CONFIG_PIC32_SERIAL) += serial_pic32.o
>>
>>  ifndef CONFIG_SPL_BUILD
>>  obj-$(CONFIG_USB_TTY) += usbtty.o
>> diff --git a/drivers/serial/serial_pic32.c b/drivers/serial/serial_pic32.c
>> new file mode 100644
>> index 0000000..ee9d056
>> --- /dev/null
>> +++ b/drivers/serial/serial_pic32.c
>> @@ -0,0 +1,199 @@
>> +/*
>> + * (c) 2015 Paul Thacker <paul.thacker@microchip.com>
>> + *
>> + * SPDX-License-Identifier:    GPL-2.0+
>> + *
>> + */
>> +#include <common.h>
>> +#include <clk.h>
>> +#include <dm.h>
>> +#include <serial.h>
>> +#include <wait_bit.h>
>> +#include <mach/pic32.h>
>> +#include <dt-bindings/clock/microchip,clock.h>
>> +
>> +DECLARE_GLOBAL_DATA_PTR;
>> +
>> +/* UART Control Registers */
>> +#define U_MOD          0x00
>> +#define U_MODCLR       (U_MOD + _CLR_OFFSET)
>> +#define U_MODSET       (U_MOD + _SET_OFFSET)
>> +#define U_STA          0x10
>> +#define U_STACLR       (U_STA + _CLR_OFFSET)
>> +#define U_STASET       (U_STA + _SET_OFFSET)
>> +#define U_TXR          0x20
>> +#define U_RXR          0x30
>> +#define U_BRG          0x40
>> +
>> +/* U_MOD bits */
>> +#define UART_ENABLE            BIT(15)
>> +
>> +/* U_STA bits */
>> +#define UART_RX_ENABLE         BIT(12)
>> +#define UART_TX_BRK            BIT(11)
>> +#define UART_TX_ENABLE         BIT(10)
>> +#define UART_TX_FULL           BIT(9)
>> +#define UART_TX_EMPTY          BIT(8)
>> +#define UART_RX_OERR           BIT(1)
>> +#define UART_RX_DATA_AVAIL     BIT(0)
>> +
>> +struct pic32_uart_priv {
>> +       void __iomem *base;
>> +       ulong uartclk;
>> +};
>> +
>> +/*
>> + * Initialize the serial port with the given baudrate.
>> + * The settings are always 8 data bits, no parity, 1 stop bit, no start bits.
>> + */
>> +static int pic32_serial_init(void __iomem *base, ulong clk, u32 baudrate)
>> +{
>> +       u32 div = DIV_ROUND_CLOSEST(clk, baudrate * 16);
>> +
>> +       /* wait for TX FIFO to empty */
>> +       wait_for_bit(__func__, base + U_STA, UART_TX_EMPTY,
>> +                    true, CONFIG_SYS_HZ, false);
>> +
>> +       /* send break */
>> +       writel(UART_TX_BRK, base + U_STASET);
>> +
>> +       /* disable and clear mode */
>> +       writel(0, base + U_MOD);
>> +       writel(0, base + U_STA);
>> +
>> +       /* set baud rate generator */
>> +       writel(div - 1, base + U_BRG);
>> +
>> +       /* enable the UART for TX and RX */
>> +       writel(UART_TX_ENABLE | UART_RX_ENABLE, base + U_STASET);
>> +
>> +       /* enable the UART */
>> +       writel(UART_ENABLE, base + U_MODSET);
>> +       return 0;
>> +}
>> +
>> +/* Check number of characters ready in RX Fifo */
> But what does it return? The number of available characters? Please
> make the comment more specific.

Good catch.
In PIC32 there is no way to know number of outstanding/pending chars in rx-fifo. Only it can be known whether there is any. I'll update the comment accordingly. 
Specifically bitwise ANDing with 'UART_RX_DATA_AVAIL' (=BIT(0)) makes result always binary (0, or 1).

>> +static int pic32_uart_pending_input(void __iomem *base)
>> +{
>> +       /* check if rx buffer overrun error has occurred */
>> +       if (readl(base + U_STA) & UART_RX_OERR) {
>> +               readl(base + U_RXR);
>> +
>> +               /* clear OERR to keep receiving */
>> +               writel(UART_RX_OERR, base + U_STACLR);
>> +       }
>> +
>> +       return readl(base + U_STA) & UART_RX_DATA_AVAIL;
>> +}
>> +
>> +static int pic32_uart_pending(struct udevice *dev, bool input)
>> +{
>> +       struct pic32_uart_priv *priv = dev_get_priv(dev);
>> +
>> +       if (input)
>> +               return pic32_uart_pending_input(priv->base);
> Should return the number of characters available. Should this be?
>
>                return pic32_uart_pending_input(priv->base) ? 1 : 0;
>
> Of course I don't quite know what pic32_uart_pending_input() does, so
> I could be wrong.

It returns in binary (0 or 1) due to short-coming in controller.

>> +
>> +       return !(readl(priv->base + U_STA) & UART_TX_EMPTY);
>> +}
>> +
>> +static int pic32_uart_setbrg(struct udevice *dev, int baudrate)
>> +{
>> +       struct pic32_uart_priv *priv = dev_get_priv(dev);
>> +
>> +       return pic32_serial_init(priv->base, priv->uartclk, baudrate);
>> +}
>> +
>> +static int pic32_uart_putc(struct udevice *dev, const char ch)
>> +{
>> +       struct pic32_uart_priv *priv = dev_get_priv(dev);
>> +
>> +       /* Check if Tx FIFO is full */
>> +       if (readl(priv->base + U_STA) & UART_TX_FULL)
>> +               return -EAGAIN;
>> +
>> +       /* pump the char to tx buffer */
>> +       writel(ch, priv->base + U_TXR);
>> +
>> +       return 0;
>> +}
>> +
>> +static int pic32_uart_getc(struct udevice *dev)
>> +{
>> +       struct pic32_uart_priv *priv = dev_get_priv(dev);
>> +
>> +       /* return error if RX fifo is empty */
>> +       if (!pic32_uart_pending_input(priv->base))
>> +               return -EAGAIN;
>> +
>> +       /* read the character from rx buffer */
>> +       return readl(priv->base + U_RXR) & 0xff;
>> +}
>> +
>> +static int pic32_uart_probe(struct udevice *dev)
>> +{
>> +       struct pic32_uart_priv *priv = dev_get_priv(dev);
>> +       struct udevice *clkdev;
>> +       fdt_addr_t addr;
>> +       fdt_size_t size;
>> +       int ret;
>> +
>> +       /* get address */
>> +       addr = fdtdec_get_addr_size(gd->fdt_blob, dev->of_offset, "reg", &size);
>> +       if (addr == FDT_ADDR_T_NONE)
>> +               return -EINVAL;
>> +
>> +       priv->base = ioremap(addr, size);
>> +       if (!priv->base)
>> +               return -EINVAL;
>> +
>> +       /* get clock rate */
>> +       ret = uclass_get_device(UCLASS_CLK, 0, &clkdev);
>> +       if (ret) {
>> +               printf("clk class not found, %d\n", ret);
>> +               return ret;
>> +       }
>> +       priv->uartclk = clk_get_periph_rate(clkdev, PB2CLK);
>> +
>> +       /* initialize serial */
>> +       return pic32_serial_init(priv->base, priv->uartclk, CONFIG_BAUDRATE);
>> +}
>> +
>> +static const struct dm_serial_ops pic32_uart_ops = {
>> +       .putc           = pic32_uart_putc,
>> +       .pending        = pic32_uart_pending,
>> +       .getc           = pic32_uart_getc,
>> +       .setbrg         = pic32_uart_setbrg,
>> +};
>> +
>> +static const struct udevice_id pic32_uart_ids[] = {
>> +       { .compatible = "microchip,pic32mzda-uart" },
>> +       {}
>> +};
>> +
>> +U_BOOT_DRIVER(pic32_serial) = {
>> +       .name           = "pic32-uart",
>> +       .id             = UCLASS_SERIAL,
>> +       .of_match       = pic32_uart_ids,
>> +       .probe          = pic32_uart_probe,
>> +       .ops            = &pic32_uart_ops,
>> +       .flags          = DM_FLAG_PRE_RELOC,
>> +       .priv_auto_alloc_size = sizeof(struct pic32_uart_priv),
>> +};
>> +
>> +#ifdef CONFIG_DEBUG_UART_PIC32
>> +#include <debug_uart.h>
>> +
>> +static inline void _debug_uart_init(void)
>> +{
>> +       void __iomem *base = (void __iomem *)CONFIG_DEBUG_UART_BASE;
>> +
>> +       pic32_serial_init(base, CONFIG_DEBUG_UART_CLOCK, CONFIG_BAUDRATE);
>> +}
>> +
>> +static inline void _debug_uart_putc(int ch)
>> +{
>> +       writel(ch, CONFIG_DEBUG_UART_BASE + U_TXR);
>> +}
>> +
>> +DEBUG_UART_FUNCS
>> +#endif
>> --
>> 1.8.3.1
>>
> Regards,
> Simon