Convert greybus/uart.c from IDR to XArray. The abstract data type XArray is more memory-efficient, parallelisable, and cache friendly. It takes advantage of RCU to perform lookups without locking. Furthermore, IDR is deprecated because XArray has a better (cleaner and more consistent) API.

Signed-off-by: Fabio M. De Francesco fmdefrancesco@gmail.com ---

v3->v4: Remove mutex_lock/unlock around xa_load(). These locks seem to be unnecessary because there is a 1:1 correspondence between a specific minor and its gb_tty and there is no reference counting. I think that the RCU locks used inside xa_load() are sufficient to protect this API from returning an invalid gb_tty in case of concurrent access. Some more considerations on this topic are in the following message to linux-kernel list: https://lore.kernel.org/lkml/3554184.2JXonMZcNW@localhost.localdomain/ v2->v3: Fix some issues according to a review by Alex Elder elder@ieee.org v1->v2: Fix an issue found by the kernel test robot. It is due to passing to xa_*lock() the same old mutex that IDR used with the previous version of the code.

drivers/staging/greybus/uart.c | 32 ++++++++++++++------------------ 1 file changed, 14 insertions(+), 18 deletions(-)

diff --git a/drivers/staging/greybus/uart.c b/drivers/staging/greybus/uart.c index 73f01ed1e5b7..f66983adb51b 100644 --- a/drivers/staging/greybus/uart.c +++ b/drivers/staging/greybus/uart.c @@ -22,7 +22,7 @@ #include <linux/serial.h> #include <linux/tty_driver.h> #include <linux/tty_flip.h> -#include <linux/idr.h> +#include <linux/xarray.h> #include <linux/fs.h> #include <linux/kdev_t.h> #include <linux/kfifo.h> @@ -32,8 +32,9 @@

#include "gbphy.h"

-#define GB_NUM_MINORS 16 /* 16 is more than enough */ -#define GB_NAME "ttyGB" +#define GB_NUM_MINORS 16 /* 16 is more than enough */ +#define GB_RANGE_MINORS XA_LIMIT(0, GB_NUM_MINORS) +#define GB_NAME "ttyGB"

#define GB_UART_WRITE_FIFO_SIZE PAGE_SIZE #define GB_UART_WRITE_ROOM_MARGIN 1 /* leave some space in fifo */ @@ -67,8 +68,7 @@ struct gb_tty { };

static struct tty_driver *gb_tty_driver; -static DEFINE_IDR(tty_minors); -static DEFINE_MUTEX(table_lock); +static DEFINE_XARRAY(tty_minors);

static int gb_uart_receive_data_handler(struct gb_operation *op) { @@ -341,8 +341,7 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor) { struct gb_tty *gb_tty;

- mutex_lock(&table_lock); - gb_tty = idr_find(&tty_minors, minor); + gb_tty = xa_load(&tty_minors, minor); if (gb_tty) { mutex_lock(&gb_tty->mutex); if (gb_tty->disconnected) { @@ -353,19 +352,18 @@ static struct gb_tty *get_gb_by_minor(unsigned int minor) mutex_unlock(&gb_tty->mutex); } } - mutex_unlock(&table_lock); return gb_tty; }

static int alloc_minor(struct gb_tty *gb_tty) { int minor; + int ret;

- mutex_lock(&table_lock); - minor = idr_alloc(&tty_minors, gb_tty, 0, GB_NUM_MINORS, GFP_KERNEL); - mutex_unlock(&table_lock); - if (minor >= 0) - gb_tty->minor = minor; + ret = xa_alloc(&tty_minors, &minor, gb_tty, GB_RANGE_MINORS, GFP_KERNEL); + if (ret) + return ret; + gb_tty->minor = minor; return minor; }

@@ -374,9 +372,7 @@ static void release_minor(struct gb_tty *gb_tty) int minor = gb_tty->minor;

gb_tty->minor = 0; /* Maybe should use an invalid value instead */ - mutex_lock(&table_lock); - idr_remove(&tty_minors, minor); - mutex_unlock(&table_lock); + xa_erase(&tty_minors, minor); }

static int gb_tty_install(struct tty_driver *driver, struct tty_struct *tty) @@ -837,7 +833,7 @@ static int gb_uart_probe(struct gbphy_device *gbphy_dev,

minor = alloc_minor(gb_tty); if (minor < 0) { - if (minor == -ENOSPC) { + if (minor == -EBUSY) { dev_err(&gbphy_dev->dev, "no more free minor numbers\n"); retval = -ENODEV; @@ -982,7 +978,7 @@ static void gb_tty_exit(void) { tty_unregister_driver(gb_tty_driver); put_tty_driver(gb_tty_driver); - idr_destroy(&tty_minors); + xa_destroy(&tty_minors); }

static const struct gbphy_device_id gb_uart_id_table[] = {