Re: [PATCH 1/3] iio: core: wrap IIO device into a iio_dev_priv object

[Jonathan Cameron]

On Fri, 8 May 2020 16:40:15 +0100
Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx> wrote:

> On Fri, 8 May 2020 17:13:04 +0300
> Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx> wrote:
> 
> > There are plenty of bad designs we want to discourage or not have to review
> > manually usually about accessing private (marked as [INTERN]) fields of
> > 'struct iio_dev'.  
> 
> This has been on the todo list for many years so great you are having a go.
>  
> > 
> > This is difficult, as a lot of users copy drivers, and not always the best
> > examples.
> > 
> > A better idea is to hide those fields into the framework.
> > For 'struct iio_dev' this is a 'struct iio_dev_priv' which wraps a public
> > 'struct iio_dev' object.
> > 
> > In the next patches, some fields will be moved to this new struct, each
> > with it's own rework.
> > 
> > This rework will not be complete[-able] for a while, as many fields need
> > some drivers to be reworked in order to finalize them
> > (e.g. 'indio_dev->mlock').
> > 
> > But some fields can already be moved, and in time, all of them may get
> > there (in the 'struct iio_dev_priv' object).
> > 
> > We also need to hide the implementations for 'iio_priv()' &
> > 'iio_priv_to_dev()', as the pointer arithmetic will not match once things
> > are moved.  
> 
> This last bit has the disadvantage of potentially putting a function
> call in some fast paths where there wasn't one before.
> 
> We may not need to 'forcefully' hide the internal parts.  May be
> enough to just make their use really obvious.  If you have to cast
> to an iio_dev_priv then you are doing something very wrong.

Note, definitely keep the to_* macro only in the private core header.

> The old stick __ in front of it may make that even more obvious.
> 
> Naming is a bit confusing though.  iio_dev_priv sounds like private
> to the device... iio_dev_opaque maybe?
> 
> 
> > 
> > Signed-off-by: Alexandru Ardelean <alexandru.ardelean@xxxxxxxxxx>
> > ---
> > 
> > Just as a note here, I've been running this patchset without a problem
> > for 2 weeks now in a work branch.
> > But it's only been a setup, so no idea if some other thing may cause
> > bigger issues.
> > 
> > This small patchset is meant to kickstart this, for GSoC people or for
> > people wanting to start contributing to IIO.
> > 
> >  drivers/iio/iio_core.h          | 11 +++++++++++
> >  drivers/iio/industrialio-core.c | 32 +++++++++++++++++++++++++++-----
> >  include/linux/iio/iio.h         | 12 ++----------
> >  3 files changed, 40 insertions(+), 15 deletions(-)
> > 
> > diff --git a/drivers/iio/iio_core.h b/drivers/iio/iio_core.h
> > index fd9a5f1d5e51..84f3b4590c05 100644
> > --- a/drivers/iio/iio_core.h
> > +++ b/drivers/iio/iio_core.h
> > @@ -17,6 +17,17 @@ struct iio_dev;
> >  
> >  extern struct device_type iio_device_type;
> >  
> > +/**
> > + * struct iio_dev_priv - industrial I/O device private information
> > + * @indio_dev:			public IIO device object
> > + */
> > +struct iio_dev_priv {
> > +	struct iio_dev			indio_dev;
> > +};
> > +
> > +#define to_iio_dev_priv(indio_dev)	\
> > +	container_of(indio_dev, struct iio_dev_priv, indio_dev)
> > +
> >  int __iio_add_chan_devattr(const char *postfix,
> >  			   struct iio_chan_spec const *chan,
> >  			   ssize_t (*func)(struct device *dev,
> > diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> > index 462d3e810013..f0888dd84d3d 100644
> > --- a/drivers/iio/industrialio-core.c
> > +++ b/drivers/iio/industrialio-core.c
> > @@ -164,6 +164,23 @@ static const char * const iio_chan_info_postfix[] = {
> >  	[IIO_CHAN_INFO_THERMOCOUPLE_TYPE] = "thermocouple_type",
> >  };
> >  
> > +
> > +void *iio_priv(const struct iio_dev *indio_dev)
> > +{
> > +	struct iio_dev_priv *iio_dev_priv = to_iio_dev_priv(indio_dev);
> > +	return (char *)iio_dev_priv + ALIGN(sizeof(struct iio_dev_priv), IIO_ALIGN);
> > +}
> > +EXPORT_SYMBOL_GPL(iio_priv);
> > +
> > +struct iio_dev *iio_priv_to_dev(void *priv)
> > +{
> > +	struct iio_dev_priv *iio_dev_priv =
> > +		(struct iio_dev_priv *)((char *)priv -
> > +				  ALIGN(sizeof(struct iio_dev_priv), IIO_ALIGN));
> > +	return &iio_dev_priv->indio_dev;
> > +}
> > +EXPORT_SYMBOL_GPL(iio_priv_to_dev);
> > +
> >  /**
> >   * iio_find_channel_from_si() - get channel from its scan index
> >   * @indio_dev:		device
> > @@ -1476,6 +1493,8 @@ static void iio_device_unregister_sysfs(struct iio_dev *indio_dev)
> >  static void iio_dev_release(struct device *device)
> >  {
> >  	struct iio_dev *indio_dev = dev_to_iio_dev(device);
> > +	struct iio_dev_priv *iio_dev_priv = to_iio_dev_priv(indio_dev);
> > +
> >  	if (indio_dev->modes & INDIO_ALL_TRIGGERED_MODES)
> >  		iio_device_unregister_trigger_consumer(indio_dev);
> >  	iio_device_unregister_eventset(indio_dev);
> > @@ -1484,7 +1503,7 @@ static void iio_dev_release(struct device *device)
> >  	iio_buffer_put(indio_dev->buffer);
> >  
> >  	ida_simple_remove(&iio_ida, indio_dev->id);
> > -	kfree(indio_dev);
> > +	kfree(iio_dev_priv);
> >  }
> >  
> >  struct device_type iio_device_type = {
> > @@ -1498,10 +1517,11 @@ struct device_type iio_device_type = {
> >   **/
> >  struct iio_dev *iio_device_alloc(int sizeof_priv)
> >  {
> > +	struct iio_dev_priv *iio_dev_priv;
> >  	struct iio_dev *dev;
> >  	size_t alloc_size;
> >  
> > -	alloc_size = sizeof(struct iio_dev);
> > +	alloc_size = sizeof(struct iio_dev_priv);
> >  	if (sizeof_priv) {
> >  		alloc_size = ALIGN(alloc_size, IIO_ALIGN);
> >  		alloc_size += sizeof_priv;
> > @@ -1509,10 +1529,12 @@ struct iio_dev *iio_device_alloc(int sizeof_priv)
> >  	/* ensure 32-byte alignment of whole construct ? */
> >  	alloc_size += IIO_ALIGN - 1;
> >  
> > -	dev = kzalloc(alloc_size, GFP_KERNEL);
> > -	if (!dev)
> > +	iio_dev_priv = kzalloc(alloc_size, GFP_KERNEL);
> > +	if (!iio_dev_priv)
> >  		return NULL;
> >  
> > +	dev = &iio_dev_priv->indio_dev;
> > +
> >  	dev->dev.groups = dev->groups;
> >  	dev->dev.type = &iio_device_type;
> >  	dev->dev.bus = &iio_bus_type;
> > @@ -1526,7 +1548,7 @@ struct iio_dev *iio_device_alloc(int sizeof_priv)
> >  	if (dev->id < 0) {
> >  		/* cannot use a dev_err as the name isn't available */
> >  		pr_err("failed to get device id\n");
> > -		kfree(dev);
> > +		kfree(iio_dev_priv);
> >  		return NULL;
> >  	}
> >  	dev_set_name(&dev->dev, "iio:device%d", dev->id);
> > diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> > index 5f9f439a4f01..38c4ea505394 100644
> > --- a/include/linux/iio/iio.h
> > +++ b/include/linux/iio/iio.h
> > @@ -678,16 +678,8 @@ static inline void *iio_device_get_drvdata(struct iio_dev *indio_dev)
> >  #define IIO_ALIGN L1_CACHE_BYTES
> >  struct iio_dev *iio_device_alloc(int sizeof_priv);
> >  
> > -static inline void *iio_priv(const struct iio_dev *indio_dev)
> > -{
> > -	return (char *)indio_dev + ALIGN(sizeof(struct iio_dev), IIO_ALIGN);
> > -}
> > -
> > -static inline struct iio_dev *iio_priv_to_dev(void *priv)
> > -{
> > -	return (struct iio_dev *)((char *)priv -
> > -				  ALIGN(sizeof(struct iio_dev), IIO_ALIGN));
> > -}
> > +void *iio_priv(const struct iio_dev *indio_dev);
> > +struct iio_dev *iio_priv_to_dev(void *priv);
> >  
> >  void iio_device_free(struct iio_dev *indio_dev);
> >  struct iio_dev *devm_iio_device_alloc(struct device *dev, int sizeof_priv);  
> 
>