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iio: industrialio-core: Fix debugfs read

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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: e553f182d5 ("staging: iio: core: Introduce debugfs support, add support for direct register access")
Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
Signed-off-by: Alexandru Tachici <alexandru.tachici@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
This commit is contained in:
Alexandru Tachici 2020-02-21 14:06:55 +02:00 committed by Jonathan Cameron
parent 2303248b29
commit 2ddc982a6c
2 changed files with 13 additions and 4 deletions
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15
drivers/iio/industrialio-core.c
View file

@ -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,

2
include/linux/iio/iio.h
View file

@ -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
};