From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: MIME-Version: 1.0 In-Reply-To: <20170820120512.31c8e98a@archlinux> References: <1500564267-8613-1-git-send-email-akinobu.mita@gmail.com> <1500564267-8613-12-git-send-email-akinobu.mita@gmail.com> <20170723130143.474dbe6d@kernel.org> <20170820120512.31c8e98a@archlinux> From: Akinobu Mita Date: Tue, 22 Aug 2017 19:20:20 +0900 Message-ID: Subject: Re: [PATCH v2 11/11] iio: adc: ti-ads1015: add threshold event support To: Jonathan Cameron Cc: linux-iio@vger.kernel.org, Daniel Baluta Content-Type: text/plain; charset="UTF-8" List-ID: 2017-08-20 20:05 GMT+09:00 Jonathan Cameron : > On Sun, 23 Jul 2017 13:01:43 +0100 > Jonathan Cameron wrote: > >> On Fri, 21 Jul 2017 00:24:27 +0900 >> Akinobu Mita wrote: >> >> > The ADS1015 device provides programmable comparator that can issue an >> > interrupt on the ALERT pin. This change adds the iio threshold event >> > support for that feature. >> > >> > The ADS1015 device only have a single config register which contains an >> > input multiplexer selection, comparator settings, and etc. So only a >> > single event channel can be enabled at a time. Also enabling both buffer >> > and event are prohibited for simplicity. >> > >> > Cc: Daniel Baluta >> > Cc: Jonathan Cameron >> > Signed-off-by: Akinobu Mita >> one really minor point inline. >> >> Otherwise I'm happy with this set. Just waiting to see if >> Daniel has time to take a look (or anyone else!) >> > > I added a really trivial check on the error as mentioned inline and > applied to the togreg branch of iio.git and pushed out as testing. > > If you could sanity check my change that would be great. I have sent version 3 of this series on 2017-07-31 that included a fix for the comparator polarity field setting in config register. Should I send a incremental patch for the missing part to the togreg branch? > Thanks, > > Jonathan > >> Jonathan >> > --- >> > drivers/iio/adc/ti-ads1015.c | 406 ++++++++++++++++++++++++++++++++++++++++++- >> > 1 file changed, 404 insertions(+), 2 deletions(-) >> > >> > diff --git a/drivers/iio/adc/ti-ads1015.c b/drivers/iio/adc/ti-ads1015.c >> > index 5568be4..54547a2 100644 >> > --- a/drivers/iio/adc/ti-ads1015.c >> > +++ b/drivers/iio/adc/ti-ads1015.c >> > @@ -17,6 +17,7 @@ >> > #include >> > #include >> > #include >> > +#include >> > #include >> > #include >> > #include >> > @@ -28,6 +29,7 @@ >> > #include >> > #include >> > #include >> > +#include >> > #include >> > #include >> > #include >> > @@ -36,17 +38,38 @@ >> > >> > #define ADS1015_CONV_REG 0x00 >> > #define ADS1015_CFG_REG 0x01 >> > +#define ADS1015_LO_THRESH_REG 0x02 >> > +#define ADS1015_HI_THRESH_REG 0x03 >> > >> > +#define ADS1015_CFG_COMP_QUE_SHIFT 0 >> > +#define ADS1015_CFG_COMP_LAT_SHIFT 2 >> > +#define ADS1015_CFG_COMP_POL_SHIFT 3 >> > +#define ADS1015_CFG_COMP_MODE_SHIFT 4 >> > #define ADS1015_CFG_DR_SHIFT 5 >> > #define ADS1015_CFG_MOD_SHIFT 8 >> > #define ADS1015_CFG_PGA_SHIFT 9 >> > #define ADS1015_CFG_MUX_SHIFT 12 >> > >> > +#define ADS1015_CFG_COMP_QUE_MASK GENMASK(1, 0) >> > +#define ADS1015_CFG_COMP_LAT_MASK BIT(2) >> > +#define ADS1015_CFG_COMP_POL_MASK BIT(2) >> > +#define ADS1015_CFG_COMP_MODE_MASK BIT(4) >> > #define ADS1015_CFG_DR_MASK GENMASK(7, 5) >> > #define ADS1015_CFG_MOD_MASK BIT(8) >> > #define ADS1015_CFG_PGA_MASK GENMASK(11, 9) >> > #define ADS1015_CFG_MUX_MASK GENMASK(14, 12) >> > >> > +/* Comparator queue and disable field */ >> > +#define ADS1015_CFG_COMP_DISABLE 3 >> > + >> > +/* Comparator polarity field */ >> > +#define ADS1015_CFG_COMP_POL_LOW 0 >> > +#define ADS1015_CFG_COMP_POL_HIGH 1 >> > + >> > +/* Comparator mode field */ >> > +#define ADS1015_CFG_COMP_MODE_TRAD 0 >> > +#define ADS1015_CFG_COMP_MODE_WINDOW 1 >> > + >> > /* device operating modes */ >> > #define ADS1015_CONTINUOUS 0 >> > #define ADS1015_SINGLESHOT 1 >> > @@ -89,6 +112,30 @@ static int ads1015_fullscale_range[] = { >> > 6144, 4096, 2048, 1024, 512, 256, 256, 256 >> > }; >> > >> > +/* >> > + * Translation from COMP_QUE field value to the number of successive readings >> > + * exceed the threshold values before an interrupt is generated >> > + */ >> > +static const int ads1015_comp_queue[] = { 1, 2, 4 }; >> > + >> > +static const struct iio_event_spec ads1015_events[] = { >> > + { >> > + .type = IIO_EV_TYPE_THRESH, >> > + .dir = IIO_EV_DIR_RISING, >> > + .mask_separate = BIT(IIO_EV_INFO_VALUE) | >> > + BIT(IIO_EV_INFO_ENABLE), >> > + }, { >> > + .type = IIO_EV_TYPE_THRESH, >> > + .dir = IIO_EV_DIR_FALLING, >> > + .mask_separate = BIT(IIO_EV_INFO_VALUE), >> > + }, { >> > + .type = IIO_EV_TYPE_THRESH, >> > + .dir = IIO_EV_DIR_EITHER, >> > + .mask_separate = BIT(IIO_EV_INFO_ENABLE) | >> > + BIT(IIO_EV_INFO_PERIOD), >> > + }, >> > +}; >> > + >> > #define ADS1015_V_CHAN(_chan, _addr) { \ >> > .type = IIO_VOLTAGE, \ >> > .indexed = 1, \ >> > @@ -105,6 +152,8 @@ static int ads1015_fullscale_range[] = { >> > .shift = 4, \ >> > .endianness = IIO_CPU, \ >> > }, \ >> > + .event_spec = ads1015_events, \ >> > + .num_event_specs = ARRAY_SIZE(ads1015_events), \ >> > .datasheet_name = "AIN"#_chan, \ >> > } >> > >> > @@ -126,6 +175,8 @@ static int ads1015_fullscale_range[] = { >> > .shift = 4, \ >> > .endianness = IIO_CPU, \ >> > }, \ >> > + .event_spec = ads1015_events, \ >> > + .num_event_specs = ARRAY_SIZE(ads1015_events), \ >> > .datasheet_name = "AIN"#_chan"-AIN"#_chan2, \ >> > } >> > >> > @@ -144,6 +195,8 @@ static int ads1015_fullscale_range[] = { >> > .storagebits = 16, \ >> > .endianness = IIO_CPU, \ >> > }, \ >> > + .event_spec = ads1015_events, \ >> > + .num_event_specs = ARRAY_SIZE(ads1015_events), \ >> > .datasheet_name = "AIN"#_chan, \ >> > } >> > >> > @@ -164,9 +217,17 @@ static int ads1015_fullscale_range[] = { >> > .storagebits = 16, \ >> > .endianness = IIO_CPU, \ >> > }, \ >> > + .event_spec = ads1015_events, \ >> > + .num_event_specs = ARRAY_SIZE(ads1015_events), \ >> > .datasheet_name = "AIN"#_chan"-AIN"#_chan2, \ >> > } >> > >> > +struct ads1015_thresh_data { >> > + unsigned int comp_queue; >> > + int high_thresh; >> > + int low_thresh; >> > +}; >> > + >> > struct ads1015_data { >> > struct regmap *regmap; >> > /* >> > @@ -176,6 +237,10 @@ struct ads1015_data { >> > struct mutex lock; >> > struct ads1015_channel_data channel_data[ADS1015_CHANNELS]; >> > >> > + unsigned int event_channel; >> > + unsigned int comp_mode; >> > + struct ads1015_thresh_data thresh_data[ADS1015_CHANNELS]; >> > + >> > unsigned int *data_rate; >> > /* >> > * Set to true when the ADC is switched to the continuous-conversion >> > @@ -185,15 +250,41 @@ struct ads1015_data { >> > bool conv_invalid; >> > }; >> > >> > +static bool ads1015_event_channel_enabled(struct ads1015_data *data) >> > +{ >> > + return (data->event_channel != ADS1015_CHANNELS); >> > +} >> > + >> > +static void ads1015_event_channel_enable(struct ads1015_data *data, int chan, >> > + int comp_mode) >> > +{ >> > + WARN_ON(ads1015_event_channel_enabled(data)); >> > + >> > + data->event_channel = chan; >> > + data->comp_mode = comp_mode; >> > +} >> > + >> > +static void ads1015_event_channel_disable(struct ads1015_data *data, int chan) >> > +{ >> > + data->event_channel = ADS1015_CHANNELS; >> > +} >> > + >> > static bool ads1015_is_writeable_reg(struct device *dev, unsigned int reg) >> > { >> > - return (reg == ADS1015_CFG_REG); >> > + switch (reg) { >> > + case ADS1015_CFG_REG: >> > + case ADS1015_LO_THRESH_REG: >> > + case ADS1015_HI_THRESH_REG: >> > + return true; >> > + default: >> > + return false; >> > + } >> > } >> > >> > static const struct regmap_config ads1015_regmap_config = { >> > .reg_bits = 8, >> > .val_bits = 16, >> > - .max_register = ADS1015_CFG_REG, >> > + .max_register = ADS1015_HI_THRESH_REG, >> > .writeable_reg = ads1015_is_writeable_reg, >> > }; >> > >> > @@ -258,6 +349,14 @@ int ads1015_get_adc_result(struct ads1015_data *data, int chan, int *val) >> > cfg = chan << ADS1015_CFG_MUX_SHIFT | pga << ADS1015_CFG_PGA_SHIFT | >> > dr << ADS1015_CFG_DR_SHIFT; >> > >> > + if (ads1015_event_channel_enabled(data)) { >> > + mask |= ADS1015_CFG_COMP_QUE_MASK | ADS1015_CFG_COMP_MODE_MASK; >> > + cfg |= data->thresh_data[chan].comp_queue << >> > + ADS1015_CFG_COMP_QUE_SHIFT | >> > + data->comp_mode << >> > + ADS1015_CFG_COMP_MODE_SHIFT; >> > + } >> > + >> > cfg = (old & ~mask) | (cfg & mask); >> > >> > ret = regmap_write(data->regmap, ADS1015_CFG_REG, cfg); >> > @@ -356,6 +455,12 @@ static int ads1015_read_raw(struct iio_dev *indio_dev, >> > if (ret) >> > break; >> > >> > + if (ads1015_event_channel_enabled(data) && >> > + data->event_channel != chan->address) { >> > + ret = -EBUSY; >> > + goto release_direct; >> > + } >> > + >> > ret = ads1015_set_power_state(data, true); >> > if (ret < 0) >> > goto release_direct; >> > @@ -421,8 +526,251 @@ static int ads1015_write_raw(struct iio_dev *indio_dev, >> > return ret; >> > } >> > >> > +static int ads1015_read_event(struct iio_dev *indio_dev, >> > + const struct iio_chan_spec *chan, enum iio_event_type type, >> > + enum iio_event_direction dir, enum iio_event_info info, int *val, >> > + int *val2) >> > +{ >> > + struct ads1015_data *data = iio_priv(indio_dev); >> > + int ret; >> > + unsigned int comp_queue; >> > + int period; >> > + int dr; >> > + >> > + mutex_lock(&data->lock); >> > + >> > + switch (info) { >> > + case IIO_EV_INFO_VALUE: >> > + *val = (dir == IIO_EV_DIR_RISING) ? >> > + data->thresh_data[chan->address].high_thresh : >> > + data->thresh_data[chan->address].low_thresh; >> > + ret = IIO_VAL_INT; >> > + break; >> > + case IIO_EV_INFO_PERIOD: >> > + dr = data->channel_data[chan->address].data_rate; >> > + comp_queue = data->thresh_data[chan->address].comp_queue; >> > + period = ads1015_comp_queue[comp_queue] * >> > + USEC_PER_SEC / data->data_rate[dr]; >> > + >> > + *val = period / USEC_PER_SEC; >> > + *val2 = period % USEC_PER_SEC; >> > + ret = IIO_VAL_INT_PLUS_MICRO; >> > + break; >> > + default: >> > + ret = -EINVAL; >> > + break; >> > + } >> > + >> > + mutex_unlock(&data->lock); >> > + >> > + return ret; >> > +} >> > + >> > +static int ads1015_write_event(struct iio_dev *indio_dev, >> > + const struct iio_chan_spec *chan, enum iio_event_type type, >> > + enum iio_event_direction dir, enum iio_event_info info, int val, >> > + int val2) >> > +{ >> > + struct ads1015_data *data = iio_priv(indio_dev); >> > + int realbits = chan->scan_type.realbits; >> > + int ret = 0; >> > + long long period; >> > + int i; >> > + int dr; >> > + >> > + mutex_lock(&data->lock); >> > + >> > + switch (info) { >> > + case IIO_EV_INFO_VALUE: >> > + if (val >= 1 << (realbits - 1) || val < -1 << (realbits - 1)) { >> > + ret = -EINVAL; >> > + break; >> > + } >> > + if (dir == IIO_EV_DIR_RISING) >> > + data->thresh_data[chan->address].high_thresh = val; >> > + else >> > + data->thresh_data[chan->address].low_thresh = val; >> > + break; >> > + case IIO_EV_INFO_PERIOD: >> > + dr = data->channel_data[chan->address].data_rate; >> > + period = val * USEC_PER_SEC + val2; >> > + >> > + for (i = 0; i < ARRAY_SIZE(ads1015_comp_queue) - 1; i++) { >> > + if (period <= ads1015_comp_queue[i] * >> > + USEC_PER_SEC / data->data_rate[dr]) >> > + break; >> > + } >> > + data->thresh_data[chan->address].comp_queue = i; >> > + break; >> > + default: >> > + ret = -EINVAL; >> > + break; >> > + } >> > + >> > + mutex_unlock(&data->lock); >> > + >> > + return ret; >> > +} >> > + >> > +static int ads1015_read_event_config(struct iio_dev *indio_dev, >> > + const struct iio_chan_spec *chan, enum iio_event_type type, >> > + enum iio_event_direction dir) >> > +{ >> > + struct ads1015_data *data = iio_priv(indio_dev); >> > + int ret = 0; >> > + >> > + mutex_lock(&data->lock); >> > + if (data->event_channel == chan->address) { >> > + switch (dir) { >> > + case IIO_EV_DIR_RISING: >> > + ret = 1; >> > + break; >> > + case IIO_EV_DIR_EITHER: >> > + ret = (data->comp_mode == ADS1015_CFG_COMP_MODE_WINDOW); >> > + break; >> > + default: >> > + ret = -EINVAL; >> > + break; >> > + } >> > + } >> > + mutex_unlock(&data->lock); >> > + >> > + return ret; >> > +} >> > + >> > +static int ads1015_enable_event_config(struct ads1015_data *data, >> > + const struct iio_chan_spec *chan, int comp_mode) >> > +{ >> > + int low_thresh = data->thresh_data[chan->address].low_thresh; >> > + int high_thresh = data->thresh_data[chan->address].high_thresh; >> > + int ret; >> > + unsigned int val; >> > + >> > + if (ads1015_event_channel_enabled(data)) { >> > + if (data->event_channel != chan->address || >> > + (data->comp_mode == ADS1015_CFG_COMP_MODE_TRAD && >> > + comp_mode == ADS1015_CFG_COMP_MODE_WINDOW)) >> > + return -EBUSY; >> > + >> > + return 0; >> > + } >> > + >> > + if (comp_mode == ADS1015_CFG_COMP_MODE_TRAD) { >> > + low_thresh = max(-1 << (chan->scan_type.realbits - 1), >> > + high_thresh - 1); >> > + } >> > + ret = regmap_write(data->regmap, ADS1015_LO_THRESH_REG, >> > + low_thresh << chan->scan_type.shift); >> > + if (ret) >> > + return ret; >> > + >> > + ret = regmap_write(data->regmap, ADS1015_HI_THRESH_REG, >> > + high_thresh << chan->scan_type.shift); >> > + if (ret) >> > + return ret; >> > + >> > + ret = ads1015_set_power_state(data, true); >> > + if (ret < 0) >> > + return ret; >> > + >> > + ads1015_event_channel_enable(data, chan->address, comp_mode); >> > + >> > + ret = ads1015_get_adc_result(data, chan->address, &val); >> > + if (ret) { >> > + ads1015_event_channel_disable(data, chan->address); >> > + ads1015_set_power_state(data, false); >> > + } >> > + >> > + return ret; >> > +} >> > + >> > +static int ads1015_disable_event_config(struct ads1015_data *data, >> > + const struct iio_chan_spec *chan, int comp_mode) >> > +{ >> > + int ret; >> > + >> > + if (!ads1015_event_channel_enabled(data)) >> > + return 0; >> > + >> > + if (data->event_channel != chan->address) >> > + return 0; >> > + >> > + if (data->comp_mode == ADS1015_CFG_COMP_MODE_TRAD && >> > + comp_mode == ADS1015_CFG_COMP_MODE_WINDOW) >> > + return 0; >> > + >> > + ret = regmap_update_bits(data->regmap, ADS1015_CFG_REG, >> > + ADS1015_CFG_COMP_QUE_MASK, >> > + ADS1015_CFG_COMP_DISABLE << >> > + ADS1015_CFG_COMP_QUE_SHIFT); >> > + if (ret) >> > + return ret; >> > + >> > + ads1015_event_channel_disable(data, chan->address); >> > + >> > + return ads1015_set_power_state(data, false); >> > +} >> > + >> > +static int ads1015_write_event_config(struct iio_dev *indio_dev, >> > + const struct iio_chan_spec *chan, enum iio_event_type type, >> > + enum iio_event_direction dir, int state) >> > +{ >> > + struct ads1015_data *data = iio_priv(indio_dev); >> > + int ret; >> > + int comp_mode = (dir == IIO_EV_DIR_EITHER) ? >> > + ADS1015_CFG_COMP_MODE_WINDOW : ADS1015_CFG_COMP_MODE_TRAD; >> > + >> > + mutex_lock(&data->lock); >> > + >> > + /* Prevent from enabling both buffer and event at a time */ >> > + ret = iio_device_claim_direct_mode(indio_dev); >> > + if (ret) { >> > + mutex_unlock(&data->lock); >> > + return ret; >> > + } >> > + >> > + if (state) >> > + ret = ads1015_enable_event_config(data, chan, comp_mode); >> > + else >> > + ret = ads1015_disable_event_config(data, chan, comp_mode); >> > + >> > + iio_device_release_direct_mode(indio_dev); >> > + mutex_unlock(&data->lock); >> > + >> > + return ret; >> > +} >> > + >> > +static irqreturn_t ads1015_event_handler(int irq, void *priv) >> > +{ >> > + struct iio_dev *indio_dev = priv; >> > + struct ads1015_data *data = iio_priv(indio_dev); >> > + int val; >> > + >> > + /* Clear the latched ALERT/RDY pin */ >> > + regmap_read(data->regmap, ADS1015_CONV_REG, &val); >> error checking? Obviously you can't do anything much with >> the error, but you don't want to muddle through the rest >> with it. >> > + >> > + if (ads1015_event_channel_enabled(data)) { >> > + enum iio_event_direction dir; >> > + u64 code; >> > + >> > + dir = data->comp_mode == ADS1015_CFG_COMP_MODE_TRAD ? >> > + IIO_EV_DIR_RISING : IIO_EV_DIR_EITHER; >> > + code = IIO_UNMOD_EVENT_CODE(IIO_VOLTAGE, data->event_channel, >> > + IIO_EV_TYPE_THRESH, dir); >> > + iio_push_event(indio_dev, code, iio_get_time_ns(indio_dev)); >> > + } >> > + >> > + return IRQ_HANDLED; >> > +} >> > + >> > static int ads1015_buffer_preenable(struct iio_dev *indio_dev) >> > { >> > + struct ads1015_data *data = iio_priv(indio_dev); >> > + >> > + /* Prevent from enabling both buffer and event at a time */ >> > + if (ads1015_event_channel_enabled(data)) >> > + return -EBUSY; >> > + >> > return ads1015_set_power_state(iio_priv(indio_dev), true); >> > } >> > >> > @@ -473,6 +821,10 @@ static const struct iio_info ads1015_info = { >> > .driver_module = THIS_MODULE, >> > .read_raw = ads1015_read_raw, >> > .write_raw = ads1015_write_raw, >> > + .read_event_value = ads1015_read_event, >> > + .write_event_value = ads1015_write_event, >> > + .read_event_config = ads1015_read_event_config, >> > + .write_event_config = ads1015_write_event_config, >> > .attrs = &ads1015_attribute_group, >> > }; >> > >> > @@ -480,6 +832,10 @@ static const struct iio_info ads1115_info = { >> > .driver_module = THIS_MODULE, >> > .read_raw = ads1015_read_raw, >> > .write_raw = ads1015_write_raw, >> > + .read_event_value = ads1015_read_event, >> > + .write_event_value = ads1015_write_event, >> > + .read_event_config = ads1015_read_event_config, >> > + .write_event_config = ads1015_write_event_config, >> > .attrs = &ads1115_attribute_group, >> > }; >> > >> > @@ -583,6 +939,7 @@ static int ads1015_probe(struct i2c_client *client, >> > struct ads1015_data *data; >> > int ret; >> > enum chip_ids chip; >> > + int i; >> > >> > indio_dev = devm_iio_device_alloc(&client->dev, sizeof(*data)); >> > if (!indio_dev) >> > @@ -617,6 +974,18 @@ static int ads1015_probe(struct i2c_client *client, >> > break; >> > } >> > >> > + data->event_channel = ADS1015_CHANNELS; >> > + /* >> > + * Set default lower and upper threshold to min and max value >> > + * respectively. >> > + */ >> > + for (i = 0; i < ADS1015_CHANNELS; i++) { >> > + int realbits = indio_dev->channels[i].scan_type.realbits; >> > + >> > + data->thresh_data[i].low_thresh = -1 << (realbits - 1); >> > + data->thresh_data[i].high_thresh = (1 << (realbits - 1)) - 1; >> > + } >> > + >> > /* we need to keep this ABI the same as used by hwmon ADS1015 driver */ >> > ads1015_get_channels_config(client); >> > >> > @@ -634,6 +1003,39 @@ static int ads1015_probe(struct i2c_client *client, >> > return ret; >> > } >> > >> > + if (client->irq) { >> > + unsigned long irq_trig = >> > + irqd_get_trigger_type(irq_get_irq_data(client->irq)); >> > + unsigned int cfg_comp_mask = ADS1015_CFG_COMP_QUE_MASK | >> > + ADS1015_CFG_COMP_LAT_MASK | ADS1015_CFG_COMP_POL_MASK; >> > + unsigned int cfg_comp = >> > + ADS1015_CFG_COMP_DISABLE << ADS1015_CFG_COMP_QUE_SHIFT | >> > + 1 << ADS1015_CFG_COMP_LAT_SHIFT; >> > + >> > + switch (irq_trig) { >> > + case IRQF_TRIGGER_LOW: >> > + cfg_comp |= ADS1015_CFG_COMP_POL_LOW; >> > + break; >> > + case IRQF_TRIGGER_HIGH: >> > + cfg_comp |= ADS1015_CFG_COMP_POL_HIGH; >> > + break; >> > + default: >> > + return -EINVAL; >> > + } >> > + >> > + ret = regmap_update_bits(data->regmap, ADS1015_CFG_REG, >> > + cfg_comp_mask, cfg_comp); >> > + if (ret) >> > + return ret; >> > + >> > + ret = devm_request_threaded_irq(&client->dev, client->irq, >> > + NULL, ads1015_event_handler, >> > + irq_trig | IRQF_ONESHOT, >> > + client->name, indio_dev); >> > + if (ret) >> > + return ret; >> > + } >> > + >> > ret = ads1015_set_conv_mode(data, ADS1015_CONTINUOUS); >> > if (ret) >> > return ret; >> >> -- >> To unsubscribe from this list: send the line "unsubscribe linux-iio" in >> the body of a message to majordomo@vger.kernel.org >> More majordomo info at http://vger.kernel.org/majordomo-info.html >