Re: [PATCH v2 6/8] iio: core: wrap IIO device into an iio_dev_opaque object

Jonathan Cameron
2020-05-16T17:29:01Z

On Thu, 14 May 2020 16:17:08 +0300
Alexandru Ardelean <alexandru.ardelean@analog.com> 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'.
>
> Sometimes users copy drivers that are 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_opaque' which wraps a public
> 'struct iio_dev' object.
>
> In the next series, 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_opaque' object).

Hopefully! This is very nice. One trivial comment inline.

>
> Since a lot of drivers also call 'iio_priv()', in order to preserve
> fast-paths (where this matters), the public iio_dev object will have a
> 'priv' field that will have the pointer to the private information already
> computed. The reference returned by this field should be guaranteed to be
> cacheline aligned.
>
> As for the 'iio_priv_to_dev()' helper, this needs to be hidden away. There
> aren't many users of this helper, and arguably drivers shouldn't need to
> use it in any fast-paths, as they can maintain a reference to the IIO
> device.
>
> The opaque parts will be moved into the 'include/linux/iio/iio-opaque.h'
> header. Should the hidden information be required for some debugging or
> some special needs, it can be made available via this header.
> Otherwise, only the IIO core files should include this file.
>
> Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
> ---
> drivers/iio/industrialio-core.c | 27 ++++++++++++++++++++++-----
> include/linux/iio/iio-opaque.h | 17 +++++++++++++++++
> include/linux/iio/iio.h | 11 +++++------
> 3 files changed, 44 insertions(+), 11 deletions(-)
> create mode 100644 include/linux/iio/iio-opaque.h
>
> diff --git a/drivers/iio/industrialio-core.c b/drivers/iio/industrialio-core.c
> index 462d3e810013..a1b29e0f8fd6 100644
> --- a/drivers/iio/industrialio-core.c
> +++ b/drivers/iio/industrialio-core.c
> @@ -25,6 +25,7 @@
> #include <linux/debugfs.h>
> #include <linux/mutex.h>
> #include <linux/iio/iio.h>
> +#include <linux/iio/iio-opaque.h>
> #include "iio_core.h"
> #include "iio_core_trigger.h"
> #include <linux/iio/sysfs.h>
> @@ -164,6 +165,15 @@ static const char * const iio_chan_info_postfix[] = {
> [IIO_CHAN_INFO_THERMOCOUPLE_TYPE] = "thermocouple_type",
> };
>
> +struct iio_dev *iio_priv_to_dev(void *priv)
> +{
> + struct iio_dev_opaque *iio_dev_opaque =
> + (struct iio_dev_opaque *)((char *)priv -
> + ALIGN(sizeof(struct iio_dev_opaque), IIO_ALIGN));
> + return &iio_dev_opaque->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 +1486,8 @@ 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_opaque *iio_dev_opaque = to_iio_dev_opaque(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 +1496,7 @@ 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_opaque);
> }
>
> struct device_type iio_device_type = {
> @@ -1498,10 +1510,11 @@ struct device_type iio_device_type = {
> **/
> struct iio_dev *iio_device_alloc(int sizeof_priv)
> {
> + struct iio_dev_opaque *iio_dev_opaque;
> struct iio_dev *dev;
> size_t alloc_size;
>
> - alloc_size = sizeof(struct iio_dev);
> + alloc_size = sizeof(struct iio_dev_opaque);
> if (sizeof_priv) {
> alloc_size = ALIGN(alloc_size, IIO_ALIGN);
> alloc_size += sizeof_priv;
> @@ -1509,10 +1522,14 @@ 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_opaque = kzalloc(alloc_size, GFP_KERNEL);
> + if (!iio_dev_opaque)
> return NULL;
>
> + dev = &iio_dev_opaque->indio_dev;
> + dev->priv = (char *)iio_dev_opaque +
> + ALIGN(sizeof(struct iio_dev_opaque), IIO_ALIGN);
> +
> dev->dev.groups = dev->groups;
> dev->dev.type = &iio_device_type;
> dev->dev.bus = &iio_bus_type;
> @@ -1526,7 +1543,7 @@ 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_opaque);
> return NULL;
> }
> dev_set_name(&dev->dev, "iio:device%d", dev->id);
> diff --git a/include/linux/iio/iio-opaque.h b/include/linux/iio/iio-opaque.h
> new file mode 100644
> index 000000000000..1375674f14cd
> --- /dev/null
> +++ b/include/linux/iio/iio-opaque.h
> @@ -0,0 +1,17 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef _INDUSTRIAL_IO_OPAQUE_H_
> +#define _INDUSTRIAL_IO_OPAQUE_H_
> +
> +/**
> + * struct iio_dev_opaque - industrial I/O device opaque information
> + * @indio_dev: public industrial I/O device information
> + */
> +struct iio_dev_opaque {
> + struct iio_dev indio_dev;
> +};
> +
> +#define to_iio_dev_opaque(indio_dev) \
> + container_of(indio_dev, struct iio_dev_opaque, indio_dev)
> +
> +#endif
> diff --git a/include/linux/iio/iio.h b/include/linux/iio/iio.h
> index 5f9f439a4f01..e82693db6578 100644
> --- a/include/linux/iio/iio.h
> +++ b/include/linux/iio/iio.h
> @@ -522,6 +522,7 @@ struct iio_buffer_setup_ops {
> * @flags: [INTERN] file ops related flags including busy flag.
> * @debugfs_dentry: [INTERN] device specific debugfs dentry.
> * @cached_reg_addr: [INTERN] cached register address for debugfs reads.
> + * @priv: [DRIVER] reference to driver's private information
Add a note to this to say it should be accessed only through the
iio_priv() route. Whilst it's not opaque we might in theory change
what it does sometime in the future - just like we are doing here :)

> */
> struct iio_dev {
> int id;
> @@ -571,6 +572,7 @@ struct iio_dev {
> char read_buf[20];
> unsigned int read_buf_len;
> #endif
> + void *priv;
> };
>
> const struct iio_chan_spec
> @@ -678,16 +680,13 @@ 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);
>
> +/* The information at this reference is guaranteed to be cacheline aligned */
> static inline void *iio_priv(const struct iio_dev *indio_dev)
> {
> - return (char *)indio_dev + ALIGN(sizeof(struct iio_dev), IIO_ALIGN);
> + return indio_dev->priv;
> }
>
> -static inline struct iio_dev *iio_priv_to_dev(void *priv)
> -{
> - return (struct iio_dev *)((char *)priv -
> - ALIGN(sizeof(struct iio_dev), IIO_ALIGN));
> -}
> +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);