linux-stable/include/linux/i2c-mux.h
Gustavo A. R. Silva 8695e0b1b9 i2c: mux: Replace zero-length array with flexible-array
The current codebase makes use of the zero-length array language
extension to the C90 standard, but the preferred mechanism to declare
variable-length types such as these ones is a flexible array member[1][2],
introduced in C99:

struct foo {
        int stuff;
        struct boo array[];
};

By making use of the mechanism above, we will get a compiler warning
in case the flexible array does not occur last in the structure, which
will help us prevent some kind of undefined behavior bugs from being
inadvertently introduced[3] to the codebase from now on.

Also, notice that, dynamic memory allocations won't be affected by
this change:

"Flexible array members have incomplete type, and so the sizeof operator
may not be applied. As a quirk of the original implementation of
zero-length arrays, sizeof evaluates to zero."[1]

sizeof(flexible-array-member) triggers a warning because flexible array
members have incomplete type[1]. There are some instances of code in
which the sizeof operator is being incorrectly/erroneously applied to
zero-length arrays and the result is zero. Such instances may be hiding
some bugs. So, this work (flexible-array member conversions) will also
help to get completely rid of those sorts of issues.

This issue was found with the help of Coccinelle.

[1] https://gcc.gnu.org/onlinedocs/gcc/Zero-Length.html
[2] https://github.com/KSPP/linux/issues/21
[3] commit 7649773293 ("cxgb3/l2t: Fix undefined behaviour")

Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
2020-05-15 11:23:49 +02:00

66 lines
1.6 KiB
C

/* SPDX-License-Identifier: GPL-2.0-or-later */
/*
*
* i2c-mux.h - functions for the i2c-bus mux support
*
* Copyright (c) 2008-2009 Rodolfo Giometti <giometti@linux.it>
* Copyright (c) 2008-2009 Eurotech S.p.A. <info@eurotech.it>
* Michael Lawnick <michael.lawnick.ext@nsn.com>
*/
#ifndef _LINUX_I2C_MUX_H
#define _LINUX_I2C_MUX_H
#ifdef __KERNEL__
#include <linux/bitops.h>
struct i2c_mux_core {
struct i2c_adapter *parent;
struct device *dev;
unsigned int mux_locked:1;
unsigned int arbitrator:1;
unsigned int gate:1;
void *priv;
int (*select)(struct i2c_mux_core *, u32 chan_id);
int (*deselect)(struct i2c_mux_core *, u32 chan_id);
int num_adapters;
int max_adapters;
struct i2c_adapter *adapter[];
};
struct i2c_mux_core *i2c_mux_alloc(struct i2c_adapter *parent,
struct device *dev, int max_adapters,
int sizeof_priv, u32 flags,
int (*select)(struct i2c_mux_core *, u32),
int (*deselect)(struct i2c_mux_core *, u32));
/* flags for i2c_mux_alloc */
#define I2C_MUX_LOCKED BIT(0)
#define I2C_MUX_ARBITRATOR BIT(1)
#define I2C_MUX_GATE BIT(2)
static inline void *i2c_mux_priv(struct i2c_mux_core *muxc)
{
return muxc->priv;
}
struct i2c_adapter *i2c_root_adapter(struct device *dev);
/*
* Called to create an i2c bus on a multiplexed bus segment.
* The chan_id parameter is passed to the select and deselect
* callback functions to perform hardware-specific mux control.
*/
int i2c_mux_add_adapter(struct i2c_mux_core *muxc,
u32 force_nr, u32 chan_id,
unsigned int class);
void i2c_mux_del_adapters(struct i2c_mux_core *muxc);
#endif /* __KERNEL__ */
#endif /* _LINUX_I2C_MUX_H */