Currently iio_debugfs_read_reg calls debugfs_reg_access
every time it is ran. Reading the same hardware register
multiple times during the same reading of a debugfs file
can cause unintended effects.
For example for each: cat iio:device0/direct_reg_access
the file_operations.read function will be called at least
twice. First will return the full length of the string in
bytes and the second will return 0.
This patch makes iio_debugfs_read_reg to call debugfs_reg_access
only when the user's buffer position (*ppos) is 0. (meaning
it is the beginning of a new reading of the debugfs file).
Fixes: e553f182d55b ("staging: iio: core: Introduce debugfs support, add support for direct register access")
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
Signed-off-by: Alexandru Tachici <alexandru.tachici@xxxxxxxxxx>
---
drivers/iio/industrialio-core.c | 15 +++++++++++----
include/linux/iio/iio.h | 2 ++
2 files changed, 13 insertions(+), 4 deletions(-)
diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
index 65ff0d067018..c4d5104934fc 100644
--- a/drivers/iio/industrialio-core.c
+++ b/drivers/iio/industrialio-core.c
@@ -301,11 +301,14 @@ static ssize_t iio_debugfs_read_reg(struct file *file, char __user *userbuf,
size_t count, loff_t *ppos)
{
struct iio_dev *indio_dev = file->private_data;
- char buf[20];
unsigned val = 0;
- ssize_t len;
int ret;
+ if (*ppos > 0)
+ return simple_read_from_buffer(userbuf, count, ppos,
+ indio_dev->read_buf,
+ indio_dev->read_buf_len);
+
ret = indio_dev->info->debugfs_reg_access(indio_dev,
indio_dev->cached_reg_addr,
0, &val);
@@ -314,9 +317,13 @@ static ssize_t iio_debugfs_read_reg(struct file *file, char __user *userbuf,
return ret;
}
- len = snprintf(buf, sizeof(buf), "0x%X\n", val);
+ indio_dev->read_buf_len = snprintf(indio_dev->read_buf,
+ sizeof(indio_dev->read_buf),
+ "0x%X\n", val);
- return simple_read_from_buffer(userbuf, count, ppos, buf, len);
+ return simple_read_from_buffer(userbuf, count, ppos,
+ indio_dev->read_buf,
+ indio_dev->read_buf_len);
}
static ssize_t iio_debugfs_write_reg(struct file *file,
diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
index 862ce0019eba..eed58ed2f368 100644
--- a/include/linux/iio/iio.h
+++ b/include/linux/iio/iio.h
@@ -568,6 +568,8 @@ struct iio_dev {
#if defined(CONFIG_DEBUG_FS)
struct dentry *debugfs_dentry;
unsigned cached_reg_addr;
+ char read_buf[20];
+ unsigned int read_buf_len;
#endif
};
--
2.20.1
