On Mon, 11 May 2020 09:16:32 +0000
"Ardelean, Alexandru" <alexandru.Ardelean@xxxxxxxxxx> wrote:
> On Fri, 2020-05-08 at 16:44 +0100, Jonathan Cameron wrote:
> > [External]
> >
> > 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.
>
> Hmm.
> I think we can change this to have a void *ptr in the public iio.h header and
> that points to the private data in the private struct, and we compute it once,
> and just return it.
>
> so:
>
> struct iio_dev_opaque;
>
> struct iio_dev {
> struct iio_dev_opaque *opaque; // compute this during iio_device_alloc()
> void *priv; // compute this during iio_device_alloc()
> };
>
> static inline void *iio_priv(const struct iio_dev *indio_dev)
> {
> return indio_dev->priv;
> }
>
> [ or even just convert it to a macro ; no preference ]
That works for me and avoids any of the messy stuff below.
Make sure to add a comment that the region that points to is guaranteed
to maintain cacheline alignment as thats hidden now.
>
> > >
> > > 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?
>
> regarding the 'opaque' part, that would be a 'struct iio_dev_opaque {' that
> lives somewhere like
>
> struct iio_dev_opaque {
> struct iio_dev indio_dev; // public IIO device part
> ... // opaque IIO device parts
> ... // iio_priv data
> }
>
> The stick __ in front, may work just fine as well.
>
> Personally, I would prefer to forcefully hide stuff, because then the compiler
> could also be useful in telling people not to use some private fields.
> People [juniors usually] listen to compilers more than they listen to review-
> comments.
> We could move the 'struct iio_dev_opaque' in 'include/linux/iio/iio-opaque.h',
> so that if they need to access some fields for some advanced/hacky debugging, it
> should work as well.
>
> Still, if it's more preferred to prefix them, I can do that as well.
> But we should prefix them as we manage to somehow make the more opaque, or
> remove the fields from places they should be used.
> Otherwise it is pointless, as people would copy 'indio_dev->__mlock' anyway.
>
>
> > >
> > >
> > > > 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);
> >
> >
