On Mon, Feb 10, 2014 at 11:19:58AM +0100, Uwe Kleine-König wrote: > This was tested on a EFM32GG-DK3750 devboard that has a temperature > sensor and an eeprom on its i2c bus. > > Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx> ping Thanks Uwe > --- > Hello, > > there are two places marked with a triple-X where I don't know if I did > it right. The one is "Do I need to protect from .master_xfer being > called again before the previous call returned?" The other is what to > return in the .functionality callback. > > Also note there is a matching entry in MAINTAINERS for "ARM/ENERGY MICRO > (SILICON LABS) EFM32 SUPPORT". > > Best regards > Uwe > > drivers/i2c/busses/Kconfig | 7 + > drivers/i2c/busses/Makefile | 1 + > drivers/i2c/busses/i2c-efm32.c | 527 ++++++++++++++++++++++++++++++++ > include/linux/platform_data/efm32-i2c.h | 15 + > 4 files changed, 550 insertions(+) > create mode 100644 drivers/i2c/busses/i2c-efm32.c > create mode 100644 include/linux/platform_data/efm32-i2c.h > > diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig > index f5ed03164d86..7322ff0c4c60 100644 > --- a/drivers/i2c/busses/Kconfig > +++ b/drivers/i2c/busses/Kconfig > @@ -432,6 +432,13 @@ config I2C_DESIGNWARE_PCI > This driver can also be built as a module. If so, the module > will be called i2c-designware-pci. > > +config I2C_EFM32 > + tristate "EFM32 I2C controller" > + depends on OF && (ARCH_EFM32 || COMPILE_TEST) > + help > + This driver supports the i2c block found in Energy Micro's EFM32 > + SoCs. > + > config I2C_EG20T > tristate "Intel EG20T PCH/LAPIS Semicon IOH(ML7213/ML7223/ML7831) I2C" > depends on PCI > diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile > index a08931fe73e1..2a56ab181851 100644 > --- a/drivers/i2c/busses/Makefile > +++ b/drivers/i2c/busses/Makefile > @@ -41,6 +41,7 @@ obj-$(CONFIG_I2C_DESIGNWARE_PLATFORM) += i2c-designware-platform.o > i2c-designware-platform-objs := i2c-designware-platdrv.o > obj-$(CONFIG_I2C_DESIGNWARE_PCI) += i2c-designware-pci.o > i2c-designware-pci-objs := i2c-designware-pcidrv.o > +obj-$(CONFIG_I2C_EFM32) += i2c-efm32.o > obj-$(CONFIG_I2C_EG20T) += i2c-eg20t.o > obj-$(CONFIG_I2C_EXYNOS5) += i2c-exynos5.o > obj-$(CONFIG_I2C_GPIO) += i2c-gpio.o > diff --git a/drivers/i2c/busses/i2c-efm32.c b/drivers/i2c/busses/i2c-efm32.c > new file mode 100644 > index 000000000000..9e860abcab63 > --- /dev/null > +++ b/drivers/i2c/busses/i2c-efm32.c > @@ -0,0 +1,527 @@ > +/* > + * Copyright (C) 2014 Uwe Kleine-Koenig for Pengutronix > + * > + * This program is free software; you can redistribute it and/or modify it under > + * the terms of the GNU General Public License version 2 as published by the > + * Free Software Foundation. > + */ > +#include <linux/module.h> > +#include <linux/platform_device.h> > +#include <linux/i2c.h> > +#include <linux/io.h> > +#include <linux/interrupt.h> > +#include <linux/err.h> > +#include <linux/clk.h> > +#include <linux/platform_data/efm32-i2c.h> > + > +#define DRIVER_NAME "efm32-i2c" > + > +#define MASK_VAL(mask, val) ((val << __ffs(mask)) & mask) > + > +#define REG_CTRL 0x00 > +#define REG_CTRL_EN 0x00001 > +#define REG_CTRL_SLAVE 0x00002 > +#define REG_CTRL_AUTOACK 0x00004 > +#define REG_CTRL_AUTOSE 0x00008 > +#define REG_CTRL_AUTOSN 0x00010 > +#define REG_CTRL_ARBDIS 0x00020 > +#define REG_CTRL_GCAMEN 0x00040 > +#define REG_CTRL_CLHR__MASK 0x00300 > +#define REG_CTRL_BITO__MASK 0x03000 > +#define REG_CTRL_BITO_OFF 0x00000 > +#define REG_CTRL_BITO_40PCC 0x01000 > +#define REG_CTRL_BITO_80PCC 0x02000 > +#define REG_CTRL_BITO_160PCC 0x03000 > +#define REG_CTRL_GIBITO 0x08000 > +#define REG_CTRL_CLTO__MASK 0x70000 > +#define REG_CTRL_CLTO_OFF 0x00000 > + > +#define REG_CMD 0x04 > +#define REG_CMD_START 0x00001 > +#define REG_CMD_STOP 0x00002 > +#define REG_CMD_ACK 0x00004 > +#define REG_CMD_NACK 0x00008 > +#define REG_CMD_CONT 0x00010 > +#define REG_CMD_ABORT 0x00020 > +#define REG_CMD_CLEARTX 0x00040 > +#define REG_CMD_CLEARPC 0x00080 > + > +#define REG_STATE 0x08 > +#define REG_STATE_BUSY 0x00001 > +#define REG_STATE_MASTER 0x00002 > +#define REG_STATE_TRANSMITTER 0x00004 > +#define REG_STATE_NACKED 0x00008 > +#define REG_STATE_BUSHOLD 0x00010 > +#define REG_STATE_STATE__MASK 0x000e0 > +#define REG_STATE_STATE_IDLE 0x00000 > +#define REG_STATE_STATE_WAIT 0x00020 > +#define REG_STATE_STATE_START 0x00040 > +#define REG_STATE_STATE_ADDR 0x00060 > +#define REG_STATE_STATE_ADDRACK 0x00080 > +#define REG_STATE_STATE_DATA 0x000a0 > +#define REG_STATE_STATE_DATAACK 0x000c0 > + > +#define REG_STATUS 0x0c > +#define REG_STATUS_PSTART 0x00001 > +#define REG_STATUS_PSTOP 0x00002 > +#define REG_STATUS_PACK 0x00004 > +#define REG_STATUS_PNACK 0x00008 > +#define REG_STATUS_PCONT 0x00010 > +#define REG_STATUS_PABORT 0x00020 > +#define REG_STATUS_TXC 0x00040 > +#define REG_STATUS_TXBL 0x00080 > +#define REG_STATUS_RXDATAV 0x00100 > + > +#define REG_CLKDIV 0x10 > +#define REG_CLKDIV_DIV__MASK 0x001ff > +#define REG_CLKDIV_DIV(div) MASK_VAL(REG_CLKDIV_DIV__MASK, (div)) > + > +#define REG_SADDR 0x14 > +#define REG_SADDRMASK 0x18 > +#define REG_RXDATA 0x1c > +#define REG_RXDATAP 0x20 > +#define REG_TXDATA 0x24 > +#define REG_IF 0x28 > +#define REG_IF_START 0x00001 > +#define REG_IF_RSTART 0x00002 > +#define REG_IF_ADDR 0x00004 > +#define REG_IF_TXC 0x00008 > +#define REG_IF_TXBL 0x00010 > +#define REG_IF_RXDATAV 0x00020 > +#define REG_IF_ACK 0x00040 > +#define REG_IF_NACK 0x00080 > +#define REG_IF_MSTOP 0x00100 > +#define REG_IF_ARBLOST 0x00200 > +#define REG_IF_BUSERR 0x00400 > +#define REG_IF_BUSHOLD 0x00800 > +#define REG_IF_TXOF 0x01000 > +#define REG_IF_RXUF 0x02000 > +#define REG_IF_BITO 0x04000 > +#define REG_IF_CLTO 0x08000 > +#define REG_IF_SSTOP 0x10000 > + > +#define REG_IFS 0x2c > +#define REG_IFC 0x30 > +#define REG_IFC__MASK 0x1ffcf > + > +#define REG_IEN 0x34 > + > +#define REG_ROUTE 0x38 > +#define REG_ROUTE_SDAPEN 0x00001 > +#define REG_ROUTE_SCLPEN 0x00002 > +#define REG_ROUTE_LOCATION__MASK 0x00700 > +#define REG_ROUTE_LOCATION(n) MASK_VAL(REG_ROUTE_LOCATION__MASK, (n)) > + > +struct efm32_i2c_ddata { > + struct i2c_adapter adapter; > + spinlock_t lock; > + > + struct clk *clk; > + void __iomem *base; > + unsigned int irq; > + struct efm32_i2c_pdata pdata; > + > + /* transfer data */ > + struct completion done; > + struct i2c_msg *msgs; > + size_t num_msgs; > + size_t current_word, current_msg; > +}; > + > +static u32 efm32_i2c_read32(struct efm32_i2c_ddata *ddata, unsigned offset) > +{ > + return readl(ddata->base + offset); > +} > + > +static void efm32_i2c_write32(struct efm32_i2c_ddata *ddata, > + unsigned offset, u32 value) > +{ > + writel(value, ddata->base + offset); > +} > + > +static void efm32_i2c_send_next_msg(struct efm32_i2c_ddata *ddata) > +{ > + struct i2c_msg *cur_msg = &ddata->msgs[ddata->current_msg]; > + > + dev_dbg(&ddata->adapter.dev, "send msg %zu/%zu (addr = %x, flags = %x, if = %08x)\n", > + ddata->current_msg, ddata->num_msgs, cur_msg->addr, > + cur_msg->flags, efm32_i2c_read32(ddata, REG_IF)); > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_START); > + efm32_i2c_write32(ddata, REG_TXDATA, cur_msg->addr << 1 | > + (cur_msg->flags & I2C_M_RD ? 1 : 0)); > +} > + > +static void efm32_i2c_send_next_byte(struct efm32_i2c_ddata *ddata) > +{ > + struct i2c_msg *cur_msg = &ddata->msgs[ddata->current_msg]; > + dev_dbg(&ddata->adapter.dev, "%s, %zu %zu\n", > + __func__, ddata->current_word, cur_msg->len); > + if (ddata->current_word >= cur_msg->len) { > + /* cur_msg completely transferred */ > + ddata->current_word = 0; > + ddata->current_msg += 1; > + > + if (ddata->current_msg >= ddata->num_msgs) { > + dev_dbg(&ddata->adapter.dev, "Stop\n"); > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_STOP); > + complete(&ddata->done); > + } else { > + efm32_i2c_send_next_msg(ddata); > + } > + } else { > + dev_dbg(&ddata->adapter.dev, "send byte %zu/%zu\n", > + ddata->current_word, cur_msg->len); > + efm32_i2c_write32(ddata, REG_TXDATA, > + cur_msg->buf[ddata->current_word++]); > + } > +} > + > +static void efm32_i2c_recv_next_byte(struct efm32_i2c_ddata *ddata) > +{ > + struct i2c_msg *cur_msg = &ddata->msgs[ddata->current_msg]; > + > + cur_msg->buf[ddata->current_word] = efm32_i2c_read32(ddata, REG_RXDATA); > + dev_dbg(&ddata->adapter.dev, "recv byte %zu/%zu: 0x%02hhx\n", > + ddata->current_word, cur_msg->len, cur_msg->buf[ddata->current_word]); > + ddata->current_word += 1; > + if (ddata->current_word >= cur_msg->len) { > + /* cur_msg completely transferred */ > + ddata->current_word = 0; > + ddata->current_msg += 1; > + > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_NACK); > + > + if (ddata->current_msg >= ddata->num_msgs) { > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_STOP); > + complete(&ddata->done); > + } else { > + efm32_i2c_send_next_msg(ddata); > + } > + } else { > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_ACK); > + } > +} > + > +static irqreturn_t efm32_i2c_irq(int irq, void *dev_id) > +{ > + struct efm32_i2c_ddata *ddata = dev_id; > + struct i2c_msg *cur_msg = &ddata->msgs[ddata->current_msg]; > + u32 irqflag = efm32_i2c_read32(ddata, REG_IF); > + u32 state = efm32_i2c_read32(ddata, REG_STATE); > + > + dev_dbg(&ddata->adapter.dev, "irq: if: %08x, state: %08x, status: %08x\n", > + irqflag, state, efm32_i2c_read32(ddata, REG_STATUS)); > + efm32_i2c_write32(ddata, REG_IFC, irqflag & REG_IFC__MASK); > + > + switch (state & REG_STATE_STATE__MASK) { > + case REG_STATE_STATE_IDLE: > + /* arbitration lost? */ > + complete(&ddata->done); > + break; > + case REG_STATE_STATE_WAIT: > + /* huh, this shouldn't happen */ > + BUG(); > + break; > + case REG_STATE_STATE_START: > + /* "caller" is expected to send an address */ > + break; > + case REG_STATE_STATE_ADDR: > + /* wait for Ack or NAck of slave */ > + break; > + case REG_STATE_STATE_ADDRACK: > + if (state & REG_STATE_NACKED) { > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_STOP); > + complete(&ddata->done); > + } else if (cur_msg->flags & I2C_M_RD) { > + /* wait for slave to send first data byte */ > + } else { > + efm32_i2c_send_next_byte(ddata); > + } > + break; > + case REG_STATE_STATE_DATA: > + if (cur_msg->flags & I2C_M_RD) { > + efm32_i2c_recv_next_byte(ddata); > + } else { > + /* wait for Ack or Nack of slave */ > + } > + break; > + case REG_STATE_STATE_DATAACK: > + if (state & REG_STATE_NACKED) { > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_STOP); > + complete(&ddata->done); > + } else { > + efm32_i2c_send_next_byte(ddata); > + } > + } > + > + return IRQ_HANDLED; > +} > + > +static int efm32_i2c_master_xfer(struct i2c_adapter *adap, > + struct i2c_msg *msgs, int num) > +{ > + struct efm32_i2c_ddata *ddata = i2c_get_adapdata(adap); > + int ret = -EBUSY; > + > + spin_lock_irq(&ddata->lock); > + > + if (ddata->msgs) > + /* > + * XXX: can .master_xfer be called when the previous is still > + * running? > + */ > + goto out_unlock; > + > + ddata->msgs = msgs; > + ddata->num_msgs = num; > + ddata->current_word = 0; > + ddata->current_msg = 0; > + > + init_completion(&ddata->done); > + > + dev_dbg(&ddata->adapter.dev, "state: %08x, status: %08x\n", > + efm32_i2c_read32(ddata, REG_STATE), > + efm32_i2c_read32(ddata, REG_STATUS)); > + > + efm32_i2c_send_next_msg(ddata); > + > + spin_unlock_irq(&ddata->lock); > + > + wait_for_completion(&ddata->done); > + > + spin_lock_irq(&ddata->lock); > + > + if (ddata->current_msg >= ddata->num_msgs) > + ret = ddata->num_msgs; > + else > + ret = -EIO; > + > + ddata->msgs = NULL; > + > +out_unlock: > + spin_unlock_irq(&ddata->lock); > + return ret; > +} > + > +static u32 efm32_i2c_functionality(struct i2c_adapter *adap) > +{ > + /* XXX: some more? */ > + return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL; > +} > + > +static const struct i2c_algorithm efm32_i2c_algo = { > + .master_xfer = efm32_i2c_master_xfer, > + .functionality = efm32_i2c_functionality, > +}; > + > +static u32 efm32_i2c_get_configured_location(struct efm32_i2c_ddata *ddata) > +{ > + u32 reg = efm32_i2c_read32(ddata, REG_ROUTE); > + > + return (reg & REG_ROUTE_LOCATION__MASK) >> > + __ffs(REG_ROUTE_LOCATION__MASK); > +} > + > +static int efm32_i2c_probe_dt(struct platform_device *pdev, > + struct efm32_i2c_ddata *ddata) > +{ > + struct device_node *np = pdev->dev.of_node; > + u32 location, frequency; > + int ret; > + > + if (!np) > + return 1; > + > + ret = of_property_read_u32(np, "location", &location); > + if (!ret) { > + dev_dbg(&pdev->dev, "using location %u\n", location); > + } else { > + /* default to location configured in hardware */ > + location = efm32_i2c_get_configured_location(ddata); > + > + dev_info(&pdev->dev, "fall back to location %u\n", location); > + } > + > + ddata->pdata.location = location; > + > + ret = of_property_read_u32(np, "clock-frequency", &frequency); > + if (!ret) { > + dev_dbg(&pdev->dev, "using frequency %u\n", frequency); > + } else { > + frequency = 100000; > + dev_info(&pdev->dev, "defaulting to 100 kHz\n"); > + } > + ddata->pdata.frequency = frequency; > + > + /* i2c core takes care about bus numbering using an alias */ > + ddata->adapter.nr = -1; > + > + return 0; > +} > + > +static int efm32_i2c_probe(struct platform_device *pdev) > +{ > + struct efm32_i2c_ddata *ddata; > + struct resource *res; > + unsigned long rate; > + int ret; > + u32 clkdiv; > + > + ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL); > + if (!ddata) { > + dev_dbg(&pdev->dev, "failed to allocate private data\n"); > + return -ENOMEM; > + } > + platform_set_drvdata(pdev, ddata); > + > + strlcpy(ddata->adapter.name, pdev->name, sizeof(ddata->adapter.name)); > + ddata->adapter.owner = THIS_MODULE; > + ddata->adapter.algo = &efm32_i2c_algo; > + ddata->adapter.dev.parent = &pdev->dev; > + ddata->adapter.dev.of_node = pdev->dev.of_node; > + i2c_set_adapdata(&ddata->adapter, ddata); > + > + spin_lock_init(&ddata->lock); > + > + ddata->clk = devm_clk_get(&pdev->dev, NULL); > + if (IS_ERR(ddata->clk)) { > + ret = PTR_ERR(ddata->clk); > + dev_err(&pdev->dev, "failed to get clock: %d\n", ret); > + return ret; > + } > + > + res = platform_get_resource(pdev, IORESOURCE_MEM, 0); > + if (!res) { > + dev_err(&pdev->dev, "failed to determine base address\n"); > + return -ENODEV; > + } > + > + if (resource_size(res) < 0x42) { > + dev_err(&pdev->dev, "memory resource too small\n"); > + return -EINVAL; > + } > + > + ddata->base = devm_ioremap_resource(&pdev->dev, res); > + if (IS_ERR(ddata->base)) > + return PTR_ERR(ddata->base); > + > + ret = platform_get_irq(pdev, 0); > + if (ret <= 0) { > + dev_err(&pdev->dev, "failed to get irq (%d)\n", ret); > + if (!ret) > + ret = -EINVAL; > + return ret; > + } > + > + ddata->irq = ret; > + > + ret = clk_prepare_enable(ddata->clk); > + if (ret < 0) { > + dev_err(&pdev->dev, "failed to enable clock (%d)\n", ret); > + return ret; > + } > + > + ret = efm32_i2c_probe_dt(pdev, ddata); > + if (ret > 0) { > + /* not created by device tree */ > + const struct efm32_i2c_pdata *pdata = > + dev_get_platdata(&pdev->dev); > + > + if (pdata) > + ddata->pdata = *pdata; > + else { > + ddata->pdata.location = > + efm32_i2c_get_configured_location(ddata); > + ddata->pdata.frequency = 100000; > + } > + > + ddata->adapter.nr = pdev->id; > + } else if (ret < 0) { > + goto err_disable_clk; > + } > + > + rate = clk_get_rate(ddata->clk); > + if (!rate) { > + dev_err(&pdev->dev, "there is no input clock available\n"); > + ret = -EIO; > + goto err_disable_clk; > + } > + clkdiv = DIV_ROUND_UP(rate, 8 * ddata->pdata.frequency) - 1; > + if (clkdiv >= 0x200) { > + dev_err(&pdev->dev, > + "input clock too fast (%lu) to divide down to bus freq (%lu)", > + rate, ddata->pdata.frequency); > + ret = -EIO; > + goto err_disable_clk; > + } > + > + dev_dbg(&pdev->dev, "input clock = %lu, bus freq = %lu, clkdiv = %lu\n", > + rate, ddata->pdata.frequency, (unsigned long)clkdiv); > + efm32_i2c_write32(ddata, REG_CLKDIV, REG_CLKDIV_DIV(clkdiv)); > + > + efm32_i2c_write32(ddata, REG_ROUTE, REG_ROUTE_SDAPEN | > + REG_ROUTE_SCLPEN | > + REG_ROUTE_LOCATION(ddata->pdata.location)); > + > + efm32_i2c_write32(ddata, REG_CTRL, REG_CTRL_EN | > + REG_CTRL_BITO_160PCC | 0 * REG_CTRL_GIBITO); > + > + efm32_i2c_write32(ddata, REG_IFC, REG_IFC__MASK); > + efm32_i2c_write32(ddata, REG_IEN, REG_IF_TXC | REG_IF_ACK | REG_IF_NACK > + | REG_IF_ARBLOST | REG_IF_BUSERR | REG_IF_RXDATAV); > + > + /* to make bus idle */ > + efm32_i2c_write32(ddata, REG_CMD, REG_CMD_ABORT); > + > + ret = request_irq(ddata->irq, efm32_i2c_irq, 0, DRIVER_NAME, ddata); > + if (ret < 0) { > + dev_err(&pdev->dev, "failed to request irq (%d)\n", ret); > + return ret; > + } > + > + ret = i2c_add_numbered_adapter(&ddata->adapter); > + if (ret) { > + dev_err(&pdev->dev, "failed to add i2c adapter (%d)\n", ret); > + free_irq(ddata->irq, ddata); > + > +err_disable_clk: > + clk_disable_unprepare(ddata->clk); > + } > + return ret; > +} > + > +static int efm32_i2c_remove(struct platform_device *pdev) > +{ > + struct efm32_i2c_ddata *ddata = platform_get_drvdata(pdev); > + > + free_irq(ddata->irq, ddata); > + clk_disable_unprepare(ddata->clk); > + > + return 0; > +} > + > +static const struct of_device_id efm32_i2c_dt_ids[] = { > + { > + .compatible = "efm32,i2c", > + }, { > + /* sentinel */ > + } > +}; > +MODULE_DEVICE_TABLE(of, efm32_i2c_dt_ids); > + > +static struct platform_driver efm32_i2c_driver = { > + .probe = efm32_i2c_probe, > + .remove = efm32_i2c_remove, > + > + .driver = { > + .name = DRIVER_NAME, > + .owner = THIS_MODULE, > + .of_match_table = efm32_i2c_dt_ids, > + }, > +}; > +module_platform_driver(efm32_i2c_driver); > + > +MODULE_AUTHOR("Uwe Kleine-Koenig <u.kleine-koenig@xxxxxxxxxxxxxx>"); > +MODULE_DESCRIPTION("EFM32 i2c driver"); > +MODULE_LICENSE("GPL v2"); > +MODULE_ALIAS("platform:" DRIVER_NAME); > diff --git a/include/linux/platform_data/efm32-i2c.h b/include/linux/platform_data/efm32-i2c.h > new file mode 100644 > index 000000000000..5e175db68bb6 > --- /dev/null > +++ b/include/linux/platform_data/efm32-i2c.h > @@ -0,0 +1,15 @@ > +#ifndef __LINUX_PLATFORM_DATA_EFM32_I2C_H__ > +#define __LINUX_PLATFORM_DATA_EFM32_I2C_H__ > + > +#include <linux/types.h> > + > +/** > + * struct efm32_i2c_pdata > + * @location: pinmux location for the I/O pins (to be written to the ROUTE > + * register) > + */ > +struct efm32_i2c_pdata { > + u8 location; > + unsigned long frequency; /* in Hz */ > +}; > +#endif /* ifndef __LINUX_PLATFORM_DATA_EFM32_I2C_H__ */ > -- > 1.8.5.2 > > -- Pengutronix e.K. | Uwe Kleine-König | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html