On 6/9/21 10:19 AM, Sa, Nuno wrote:
Hi Henk,
From: Henk Medenblik <iio-developer@xxxxxxxxxx>
Sent: Wednesday, June 9, 2021 9:04 AM
To: Alexandru Ardelean <ardeleanalex@xxxxxxxxx>; Henk Medenblik
<iio-developer@xxxxxxxxxx>
Cc: linux-iio <linux-iio@xxxxxxxxxxxxxxx>
Subject: Re: active_scan_mask
[External]
Dear Alexandru,
Hmm, so the "zerocopy" branch isn't at v0.21.
It's something much older [ ~6 years ? ].
Though the kernel active scan mask is unrelated to libiio, since
iio_readdev is being used in different sessions.
The 4.14 version of the kernel, isn't quite new.
There was some recent fix with regards to active scan-mask
computation.
But I am not sure if it's related to this.
Will try to make some time to do some testing on this.
I believe it is a bug which still exists in the adi linux kernel sources.
In industrialio-buffer.c :
static int iio_channel_mask_clear(struct iio_dev *indio_dev,
struct iio_buffer *buffer, int bit)
{
unsigned int ch;
clear_bit(bit, buffer->channel_mask);
memset(buffer->scan_mask, 0,
BITS_TO_LONGS(indio_dev->masklength)); <---------
for_each_set_bit(ch, buffer->channel_mask, indio_dev-
num_channels)
set_bit(indio_dev->channels[ch].scan_index, buffer-
scan_mask);
return 0;
}
Take a look at [1] for more details. Long story short, I think this is here because we have
some devices where we have bit granularity. Hence, we map all channels to the same
scan_index and to distinguish which channels are enabled, we could not use the current
upstream implementation. I remember some talks about this but not actual patches
came from it (I will have to go over those emails to see if I can come up with some
patches).
Regarding the memset, that looks like a bug. I guess we want:
memset(buffer->scan_mask, 0, BITS_TO_LONGS(indio_dev->masklength) * sizeof(*buffer->scan_mask));
Ccing Lars as he implemented this patches and might have something to add to
your questions.
Yea, my fault, sorry. The patch looks good.
