Be more careful with the amount of data we read from the iio dev fd

The iio drivers we have operate with a buffer length set at 2, and
can be set at larger sizes, however the current event integration
code path only handles a iio device report per loop.

For now, simply make sure we only read a single "scan", a.k.a. iio
device report, per loop. This could avoid dropping events if the
driver is producing them faster than we can consume them.

Change-Id: Ibfad7abbd445d6aae0345e2c828ca72c555c42ea
Signed-off-by: Patrick Porlan <patrick.porlan@intel.com>

diff --git a/common.h b/common.h
index 977d810..0dfa098 100644 (file)
--- a/common.h
+++ b/common.h
@@ -29,6 +29,7 @@
 
 #define MAX_TYPE_SPEC_LEN 32   /* Channel type spec len; ex: "le:u10/16>>0" */
 #define MAX_SENSOR_REPORT_SIZE 32      /* Sensor report buffer size */
+#define MAX_DEVICE_REPORT_SIZE 32      /* iio device scan buffer size */
 
 #define MAX_NAME_SIZE          32
 

diff --git a/control.c b/control.c
index 9d88047..9416d4a 100644 (file)
--- a/control.c
+++ b/control.c
@@ -25,7 +25,7 @@ static int trig_sensors_per_dev[MAX_DEVICES]; /* trigger, event based */
 
 static int device_fd[MAX_DEVICES];   /* fd on the /dev/iio:deviceX file */
 static int has_iio_ts[MAX_DEVICES];  /* ts channel available on this iio dev */
-
+static int expected_dev_report_size[MAX_DEVICES]; /* expected iio scan len */
 static int poll_fd; /* epoll instance covering all enabled sensors */
 
 static int active_poll_sensors; /* Number of enabled poll-mode sensors */
@@ -288,6 +288,20 @@ void build_sensor_report_maps (int dev_num)
 
        /* Enable the timestamp channel if there is one available */
        enable_iio_timestamp(dev_num, known_channels);
+
+       /* Add padding and timestamp size if it's enabled on this iio device */
+       if (has_iio_ts[dev_num])
+               offset = (offset+7)/8*8 + sizeof(int64_t);
+
+       expected_dev_report_size[dev_num] = offset;
+       ALOGI("Expecting %d scan length on iio dev %d\n", offset, dev_num);
+
+       if (expected_dev_report_size[dev_num] > MAX_DEVICE_REPORT_SIZE) {
+               ALOGE("Unexpectedly large scan buffer on iio dev%d: %d bytes\n",
+                     dev_num, expected_dev_report_size[dev_num]);
+
+               expected_dev_report_size[dev_num] = MAX_DEVICE_REPORT_SIZE;
+       }
 }
 
 
@@ -828,7 +842,7 @@ static int integrate_device_report (int dev_num)
 {
        int len;
        int s,c;
-       unsigned char buf[MAX_SENSOR_REPORT_SIZE] = { 0 };
+       unsigned char buf[MAX_DEVICE_REPORT_SIZE] = { 0 };
        int sr_offset;
        unsigned char *target;
        unsigned char *source;
@@ -848,7 +862,7 @@ static int integrate_device_report (int dev_num)
                return -1;
        }
 
-       len = read(device_fd[dev_num], buf, MAX_SENSOR_REPORT_SIZE);
+       len = read(device_fd[dev_num], buf, expected_dev_report_size[dev_num]);
 
        if (len == -1) {
                ALOGE("Could not read report from iio device %d (%s)\n",
@@ -902,7 +916,7 @@ static int integrate_device_report (int dev_num)
        ts_offset = (ts_offset + 7)/8*8;
 
        /* If we read an amount of data consistent with timestamp presence */
-       if (len == ts_offset + (int) sizeof(int64_t))
+       if (len == expected_dev_report_size[dev_num])
                ts = *(int64_t*) (buf + ts_offset);
 
        if (ts == 0) {