read_raw when buffered sampling enabled

read_raw when buffered sampling enabled

[Gregor Boirie]

Greetings,

I see in several iio drivers supporting triggered buffer mode that read_raw
returns -EBUSY when buffered sampling is enabled. This additional logic
is implemented in read_raw using iio_buffer_enabled().
Since some drivers don't implement this I'm wondering wether this logic is
an IIO design requirement or if this is device / driver specific.

Regards,
Grégor.

Re: read_raw when buffered sampling enabled

[Jonathan Cameron]

On 12 February 2016 10:05:11 GMT+00:00, Gregor Boirie <gregor.boirie@parrot.com> wrote:
>Greetings,
>
>I see in several iio drivers supporting triggered buffer mode that
>read_raw
>returns -EBUSY when buffered sampling is enabled. This additional logic
>is implemented in read_raw using iio_buffer_enabled().
>Since some drivers don't implement this I'm wondering wether this logic
>is
>an IIO design requirement or if this is device / driver specific.

Driver specific. Usually depends on whether such a read will
 materially effect capture to a buffer.  So usually prevent
 reads if for example a new data interrupt would be skipped
 or a sequence of data disrupted.

Some devices will read a last captured value out without
 effecting the flow so don't need to prevent such reads.

Others do every read on demand, so other than possible bus congestion, there is no
 reason to prevent such reads (and congestion is largely beyond our control,
 is we don't lock the bus up,  anyway so who cares!)

I have thought about adding some caching in the core to allow in kernel
 polled and push clients to run at the same time but that would require explicit
 notice that a polled client might want the data and some fun with an additional
 cache buffer attached.


Jonathan
>
>Regards,
>Grégor.
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