On Thu, 2024-03-28 at 15:16 +0000, Jonathan Cameron wrote:
> On Thu, 28 Mar 2024 14:22:32 +0100
> Nuno Sa via B4 Relay <devnull+nuno.sa.analog.com@xxxxxxxxxx> wrote:
>
> > From: Nuno Sa <nuno.sa@xxxxxxxxxx>
> >
> > This adds the needed backend ops for supporting a backend inerfacing
> > with an high speed dac. The new ops are:
> >
> > * data_source_set();
> > * set_sampling_freq();
> > * extend_chan_spec();
> > * ext_info_set();
> > * ext_info_get().
> >
> > Also to note the new helpers that are meant to be used by the backends
> > when extending an IIO channel (adding extended info):
> >
> > * iio_backend_ext_info_set();
> > * iio_backend_ext_info_get().
> >
> > Signed-off-by: Nuno Sa <nuno.sa@xxxxxxxxxx>
> I'm pretty flexible on this so far as I think we are still learning how front
> ends and backends should interact. Maybe we'll figure that out in the medium
> term and rework this stuff. For now it looks fine. A few minor things inline.
> >
> > +/**
> > + * iio_backend_ext_info_get - IIO ext_info read callback
> > + * @indio_dev: IIO device
> > + * @private: Data private to the driver
> > + * @chan: IIO channel
> > + * @buf: Buffer where to place the attribute data
> > + *
> > + * This helper is intended to be used by backends that extend an IIO channel
> > + * (trough iio_backend_extend_chan_spec()) with extended info. In that case,
> > + * backends are not supposed to give their own callbacks (as they would not
> > + * a way to get te backend from indio_dev). This is the getter.
>
> te->the?
Yes and some more typos :).
>
>
> > +/**
> > + * iio_backend_extend_chan_spec - Extend an IIO channel
> > + * @indio_dev: IIO device
> > + * @back: Backend device
> > + * @chan: IIO channel
> > + *
> > + * Some backends may have their own functionalities and hence capable of
> > + * extending a frontend's channel.
> > + *
> > + * RETURNS:
> > + * 0 on success, negative error number on failure.
> > + */
> > +int iio_backend_extend_chan_spec(struct iio_dev *indio_dev,
> > + struct iio_backend *back,
> > + struct iio_chan_spec *chan)
> > +{
> > + const struct iio_chan_spec_ext_info *ext_info = chan->ext_info;
> This is getting confusing. So this one is the front end value of ext_info?
> Name it as such frontend_ext_info
Yes, it's the frontend pointer. Just to enforce the below constrain. Will rename as
suggested.
>
> > + int ret;
> > +
> > + ret = iio_backend_op_call(back, extend_chan_spec, chan);
> > + if (ret)
> > + return ret;
> > + /*
> > + * Let's keep things simple for now. Don't allow to overwrite the
> > + * frontend's extended info. If ever needed, we can support appending
> > + * it.
> > + */
> > + if (ext_info && chan->ext_info != ext_info)
> > + return -EOPNOTSUPP;
> > + if (!chan->ext_info)
>
> This is checking if the backend added anything? Perhaps a comment on that
> as we don't need a backend_ext_info local variable...
Yes, but just regarding ext_info as that is the only thing we're handling below
(doing some sanity checks). Note that (as you said above) I'm keeping things a bit
"open" in that the backend is open to extend whatever it wants. With time we may
learn better what do we want constrain or not.
>
> > + return 0;
> > + /*
> > + * !\NOTE: this will break as soon as we have multiple backends on one
> > + * frontend and all of them extend channels. In that case, the core
> > + * backend code has no way to get the correct backend given the
> > + * iio device.
> > + *
> > + * One solution for this could be introducing a new backend
> > + * dedicated callback in struct iio_info so we can callback into the
> > + * frontend so it can give us the right backend given a chan_spec.
> > + */
>
> Hmm. This is indeed messy. Could we associate it with the buffer as presuably
> a front end with multiple backends is using multiple IIO buffers?
>
Hmm, the assumption of having multiple buffers seems plausible to me but considering
the example we have in hands it would be cumbersome to get the backend. Considering
iio_backend_ext_info_get(), how could we get the backend if it was associated to one
of the IIO buffers? I think we would need more "intrusive" changes to make that work
or do you have something in mind=
> As you say a dance via the front end would work fine.
I'm happy you're also open for a proper solution already. I mention this in the
cover. My idea was something like (consider the iio_backend_ext_info_get()):
if (!indio_dev->info->get_iio_backend())
return -EOPNOTSUPP;
back = indio_dev->info->get_iio_backend(indio_dev, chan_spec);
It would be nice to have some "default/generic" implementation for cases where we
only have one backend per frontend so that the frontend would not need to define the
callback.
>
>
> > + iio_device_set_drvdata(indio_dev, back);
> > +
> > + /* Don't allow backends to get creative and force their own handlers */
> > + for (ext_info = chan->ext_info; ext_info->name; ext_info++) {
> > + if (ext_info->read != iio_backend_ext_info_get)
> > + return -EINVAL;
> > + if (ext_info->write != iio_backend_ext_info_set)
> > + return -EINVAL;
> > + }
> > +
> > + return 0;
> > +}
> > +EXPORT_SYMBOL_NS_GPL(iio_backend_extend_chan_spec, IIO_BACKEND);
>
> > diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
> > index a6d79381866e..09ff2f8f9fd8 100644
> > --- a/include/linux/iio/backend.h
> > +++ b/include/linux/iio/backend.h
> > @@ -4,6 +4,7 @@
> >
> > #include <linux/types.h>
> >
> > +struct iio_chan_spec;
> > struct fwnode_handle;
> > struct iio_backend;
> > struct device;
> > @@ -15,6 +16,26 @@ enum iio_backend_data_type {
> > IIO_BACKEND_DATA_TYPE_MAX
> > };
> >
> > +enum iio_backend_data_source {
> > + IIO_BACKEND_INTERNAL_CW,
>
> CW? Either expand out what ever that is in definition of add a comment
> at least.
Continuous wave :)
>
> > + IIO_BACKEND_EXTERNAL,
> What does external mean in this case?
In this particular case comes from a DMA source (IP). I thought external to be more
generic but if you prefer, I can do something like IIO_BACKEND_DMA?
> > + IIO_BACKEND_DATA_SOURCE_MAX
> > +};
> > +
> > +/**
> > + * IIO_BACKEND_EX_INFO - Helper for an IIO extended channel attribute
> > + * @_name: Attribute name
> > + * @_shared: Whether the attribute is shared between all channels
> > + * @_what: Data private to the driver
> > + */
> > +#define IIO_BACKEND_EX_INFO(_name, _shared, _what) { \
> > + .name = (_name), \
> > + .shared = (_shared), \
> > + .read = iio_backend_ext_info_get, \
> > + .write = iio_backend_ext_info_set, \
> > + .private = (_what), \
> > +}
> > +
> > /**
> > * struct iio_backend_data_fmt - Backend data format
> > * @type: Data type.
> > @@ -35,8 +56,13 @@ struct iio_backend_data_fmt {
> > * @chan_enable: Enable one channel.
> > * @chan_disable: Disable one channel.
> > * @data_format_set: Configure the data format for a specific channel.
> > + * @data_source_set: Configure the data source for a specific channel.
> > + * @set_sample_rate: Configure the sampling rate for a specific channel.
> > * @request_buffer: Request an IIO buffer.
> > * @free_buffer: Free an IIO buffer.
> > + * @extend_chan_spec: Extend an IIO channel.
> > + * @ext_info_set: Extended info setter.
> > + * @ext_info_get: Extended info getter.
> > **/
> > struct iio_backend_ops {
> > int (*enable)(struct iio_backend *back);
> > @@ -45,10 +71,21 @@ struct iio_backend_ops {
> > int (*chan_disable)(struct iio_backend *back, unsigned int chan);
> > int (*data_format_set)(struct iio_backend *back, unsigned int chan,
> > const struct iio_backend_data_fmt *data);
> > + int (*data_source_set)(struct iio_backend *back, unsigned int chan,
> > + enum iio_backend_data_source data);
> > + int (*set_sample_rate)(struct iio_backend *back, unsigned int chan,
> > + u64 sample_rate);
>
> Name the parameter that so we know the units. _hz?
yes. And u64 to not fall in the CCF problem for 32bits :)
- Nuno Sá
