On Sun, 29 Jan 2023 19:05:23 +0100
Andreas Feldner <pelzi@xxxxxxxxxxxxxxx> wrote:
> Currently, IRQs for both falling and raising edges of the GPIO
> line connected to the DHT11 device are requested. However, the
> low states do not carry information, it is possible to determine
> 0 and 1 bits from the timing of two adjacent falling edges as
> well.
>
> Doing so does no longer requires to read the GPIO line value
> within the IRQ handler, plus halves the number of IRQs to be
> handled at all.
>
> Signed-off-by: Andreas Feldner <pelzi@xxxxxxxxxxxxxxx>
+CC Harald Not been that many years since Harald replied, so address
may still be good.
> ---
> drivers/iio/humidity/dht11.c | 28 +++++++++++-----------------
> 1 file changed, 11 insertions(+), 17 deletions(-)
>
> diff --git a/drivers/iio/humidity/dht11.c b/drivers/iio/humidity/dht11.c
> index c97e25448772..d1cd053c5dd4 100644
> --- a/drivers/iio/humidity/dht11.c
> +++ b/drivers/iio/humidity/dht11.c
> @@ -30,13 +30,13 @@
>
> #define DHT11_DATA_VALID_TIME 2000000000 /* 2s in ns */
>
> -#define DHT11_EDGES_PREAMBLE 2
> +#define DHT11_EDGES_PREAMBLE 1
> #define DHT11_BITS_PER_READ 40
> /*
> * Note that when reading the sensor actually 84 edges are detected, but
> * since the last edge is not significant, we only store 83:
> */
> -#define DHT11_EDGES_PER_READ (2 * DHT11_BITS_PER_READ + \
> +#define DHT11_EDGES_PER_READ (DHT11_BITS_PER_READ + \
> DHT11_EDGES_PREAMBLE + 1)
>
> /*
> @@ -46,6 +46,7 @@
> * 1-bit: 68-75uS -- typically 70uS (AM2302)
> * The acutal timings also depend on the properties of the cable, with
> * longer cables typically making pulses shorter.
> + * Low time is constant 50uS.
> *
> * Our decoding depends on the time resolution of the system:
> * timeres > 34uS ... don't know what a 1-tick pulse is
> @@ -63,7 +64,8 @@
> #define DHT11_START_TRANSMISSION_MIN 18000 /* us */
> #define DHT11_START_TRANSMISSION_MAX 20000 /* us */
> #define DHT11_MIN_TIMERES 34000 /* ns */
> -#define DHT11_THRESHOLD 49000 /* ns */
> +#define DHT11_LOW 50000 /* ns */
> +#define DHT11_THRESHOLD (49000 + DHT11_LOW) /* ns */
> #define DHT11_AMBIG_LOW 23000 /* ns */
> #define DHT11_AMBIG_HIGH 30000 /* ns */
>
> @@ -83,7 +85,7 @@ struct dht11 {
>
> /* num_edges: -1 means "no transmission in progress" */
> int num_edges;
> - struct {s64 ts; int value; } edges[DHT11_EDGES_PER_READ];
> + struct {s64 ts; } edges[DHT11_EDGES_PER_READ];
> };
>
> #ifdef CONFIG_DYNAMIC_DEBUG
> @@ -99,7 +101,7 @@ static void dht11_edges_print(struct dht11 *dht11)
> for (i = 1; i < dht11->num_edges; ++i) {
> dev_dbg(dht11->dev, "%d: %lld ns %s\n", i,
> dht11->edges[i].ts - dht11->edges[i - 1].ts,
> - dht11->edges[i - 1].value ? "high" : "low");
> + "falling");
> }
> }
> #endif /* CONFIG_DYNAMIC_DEBUG */
> @@ -125,14 +127,8 @@ static int dht11_decode(struct dht11 *dht11, int offset)
> unsigned char temp_int, temp_dec, hum_int, hum_dec, checksum;
>
> for (i = 0; i < DHT11_BITS_PER_READ; ++i) {
> - t = dht11->edges[offset + 2 * i + 2].ts -
> - dht11->edges[offset + 2 * i + 1].ts;
> - if (!dht11->edges[offset + 2 * i + 1].value) {
> - dev_dbg(dht11->dev,
> - "lost synchronisation at edge %d\n",
> - offset + 2 * i + 1);
> - return -EIO;
> - }
> + t = dht11->edges[offset + i + 1].ts -
> + dht11->edges[offset + i].ts;
> bits[i] = t > DHT11_THRESHOLD;
> }
>
> @@ -174,9 +170,7 @@ static irqreturn_t dht11_handle_irq(int irq, void *data)
> struct dht11 *dht11 = iio_priv(iio);
>
> if (dht11->num_edges < DHT11_EDGES_PER_READ && dht11->num_edges >= 0) {
> - dht11->edges[dht11->num_edges].ts = ktime_get_boottime_ns();
> - dht11->edges[dht11->num_edges++].value =
> - gpiod_get_value(dht11->gpiod);
> + dht11->edges[dht11->num_edges++].ts = ktime_get_boottime_ns();
>
> if (dht11->num_edges >= DHT11_EDGES_PER_READ)
> complete(&dht11->completion);
> @@ -224,7 +218,7 @@ static int dht11_read_raw(struct iio_dev *iio_dev,
> goto err;
>
> ret = request_irq(dht11->irq, dht11_handle_irq,
> - IRQF_TRIGGER_RISING | IRQF_TRIGGER_FALLING,
> + IRQF_TRIGGER_FALLING,
> iio_dev->name, iio_dev);
> if (ret)
> goto err;
