Re: [PATCH v4 06/11] iio: backend: extend features

["Nuno Sá" <noname.nuno@gmail.com>]

On Sun, 2024-10-06 at 14:48 +0100, Jonathan Cameron wrote:
> On Fri, 4 Oct 2024 15:45:21 +0200
> Angelo Dureghello <adureghello@baylibre.com> wrote:
> 
> > Hi Nuno,
> > 
> > On 04.10.2024 14:54, Nuno Sá wrote:
> > > On Thu, 2024-10-03 at 19:29 +0200, Angelo Dureghello wrote:  
> > > > From: Angelo Dureghello <adureghello@baylibre.com>
> > > > 
> > > > Extend backend features with new calls needed later on this
> > > > patchset from axi version of ad3552r.
> > > > 
> > > > The follwoing calls are added:
> > > > 
> > > > iio_backend_ddr_enable
> > > > 	enable ddr bus transfer
> > > > iio_backend_ddr_disable
> > > > 	disable ddr bus transfer
> > > > iio_backend_buffer_enable
> > > > 	enable buffer
> > > > iio_backend_buffer_disable
> > > > 	disable buffer
> > > > iio_backend_data_transfer_addr
> > > > 	define the target register address where the DAC sample
> > > > 	will be written.
> > > > 
> > > > Signed-off-by: Angelo Dureghello <adureghello@baylibre.com>
> > > > ---
> > > >  drivers/iio/industrialio-backend.c | 79
> > > > ++++++++++++++++++++++++++++++++++++++
> > > >  include/linux/iio/backend.h        | 17 ++++++++
> > > >  2 files changed, 96 insertions(+)
> > > > 
> > > > diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> > > > backend.c
> > > > index 20b3b5212da7..d5e0a4da761e 100644
> > > > --- a/drivers/iio/industrialio-backend.c
> > > > +++ b/drivers/iio/industrialio-backend.c
> > > > @@ -718,6 +718,85 @@ static int __devm_iio_backend_get(struct device *dev,
> > > > struct
> > > > iio_backend *back)
> > > >  	return 0;
> > > >  }
> > > >  
> > > > +/**
> > > > + * iio_backend_ddr_enable - Enable interface DDR (Double Data Rate) mode
> > > > + * @back: Backend device
> > > > + *
> > > > + * Enable DDR, data is generated by the IP at each front (raising and
> > > > falling)
> > > > + * of the bus clock signal.
> > > > + *
> > > > + * RETURNS:
> > > > + * 0 on success, negative error number on failure.
> > > > + */
> > > > +int iio_backend_ddr_enable(struct iio_backend *back)
> > > > +{
> > > > +	return iio_backend_op_call(back, ddr_enable);
> > > > +}
> > > > +EXPORT_SYMBOL_NS_GPL(iio_backend_ddr_enable, IIO_BACKEND);
> > > > +
> > > > +/**
> > > > + * iio_backend_ddr_disable - Disable interface DDR (Double Data Rate) mode
> > > > + * @back: Backend device
> > > > + *
> > > > + * Disable DDR, setting into SDR mode (Single Data Rate).
> > > > + *
> > > > + * RETURNS:
> > > > + * 0 on success, negative error number on failure.
> > > > + */
> > > > +int iio_backend_ddr_disable(struct iio_backend *back)
> > > > +{
> > > > +	return iio_backend_op_call(back, ddr_disable);
> > > > +}
> > > > +EXPORT_SYMBOL_NS_GPL(iio_backend_ddr_disable, IIO_BACKEND);
> > > > +
> > > > +/**
> > > > + * iio_backend_dma_stream_enable - Enable iio buffering
> > > > + * @back: Backend device
> > > > + *
> > > > + * Enabling sending the dma data stream over the bus.
> > > > + * bus interface.
> > > > + *
> > > > + * RETURNS:
> > > > + * 0 on success, negative error number on failure.
> > > > + */
> > > > +int iio_backend_dma_stream_enable(struct iio_backend *back)
> > > > +{
> > > > +	return iio_backend_op_call(back, dma_stream_enable);
> > > > +}
> > > > +EXPORT_SYMBOL_NS_GPL(iio_backend_dma_stream_enable, IIO_BACKEND);
> > > > +
> > > > +/**
> > > > + * iio_backend_dma_stream_disable - Disable iio buffering
> > > > + * @back: Backend device
> > > > + *
> > > > + * Disable sending the dma data stream over the bus.
> > > > + *
> > > > + * RETURNS:
> > > > + * 0 on success, negative error number on failure.
> > > > + */
> > > > +int iio_backend_dma_stream_disable(struct iio_backend *back)
> > > > +{
> > > > +	return iio_backend_op_call(back, dma_stream_disable);
> > > > +}
> > > > +EXPORT_SYMBOL_NS_GPL(iio_backend_dma_stream_disable, IIO_BACKEND);
> > > > +  
> > > 
> > > I'm not sure if this is what Jonathan was suggesting... Ate least I don't
> > > really
> > > agree with it. I mean, yes, this is about buffering and to start receiving (or
> > > sending) a stream of data. But AFAICT, it might have nothing to do with DMA.
> > > Same as
> > > .request_buffer() - It's pretty much always a DMA one but we should not take
> > > that for
> > > granted.
> 
> Agreed. The stream bit works, the DMA is more tenuous.  Maybe *data_stream_enable()
> is generic enough.
> 
> > > 
> > > So going back to the RFC [1], you can see I was suggesting something like
> > > struct
> > > iio_buffer_setup_ops. Maybe just add the ones we use for now? So that would
> > > be.buffer_postenable() and .buffer_predisable(). Like this, it should be
> > > obvious the
> > > intent of the ops.
> > >   
> > ok, thanks,
> > 
> > so something as :
> > 
> > struct iio_backend_setup_ops {
> > 	int (*buffer_postenable)(struct iio_backend *back);
> > 	int (*buffer_predisable)(struct iio_backend *back);
> 

For me the above is ok as it goes in line with what we currently have. But I was not
aware that Jonathan was not 100% with that naming :). So, *data_stream_enable() also
seems like a good fit to me (and I agree it's more clear about the intent of the
function). To sum it up, I'm fine with either option.

- Nuno Sá