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SubjectRe: [PATCHv4 05/17] pps: access pps device by direct pointer
On Thu, Nov 18, 2010 at 07:00:58PM +0300, Alexander Gordeev wrote:
> Using device index as a pointer needs some unnecessary work to be done
> every time the pointer is needed (in irq handler for example).
> Using a direct pointer is much more easy (and safe as well).
>
> Signed-off-by: Alexander Gordeev <lasaine@lvk.cs.msu.su>
> ---
> drivers/pps/clients/pps-ktimer.c | 30 ++++-----
> drivers/pps/clients/pps-ldisc.c | 52 ++++++++++------
> drivers/pps/kapi.c | 124 +++++++++-----------------------------
> drivers/pps/pps.c | 22 ++-----
> include/linux/pps_kernel.h | 23 +++----
> 5 files changed, 90 insertions(+), 161 deletions(-)
>
> diff --git a/drivers/pps/clients/pps-ktimer.c b/drivers/pps/clients/pps-ktimer.c
> index e1bdd8b..966ead1 100644
> --- a/drivers/pps/clients/pps-ktimer.c
> +++ b/drivers/pps/clients/pps-ktimer.c
> @@ -31,7 +31,7 @@
> * Global variables
> */
>
> -static int source;
> +static struct pps_device *pps;
> static struct timer_list ktimer;
>
> /*
> @@ -47,7 +47,7 @@ static void pps_ktimer_event(unsigned long ptr)
>
> pr_info("PPS event at %lu\n", jiffies);
>
> - pps_event(source, &ts, PPS_CAPTUREASSERT, NULL);
> + pps_event(pps, &ts, PPS_CAPTUREASSERT, NULL);
>
> mod_timer(&ktimer, jiffies + HZ);
> }
> @@ -56,12 +56,11 @@ static void pps_ktimer_event(unsigned long ptr)
> * The echo function
> */
>
> -static void pps_ktimer_echo(int source, int event, void *data)
> +static void pps_ktimer_echo(struct pps_device *pps, int event, void *data)
> {
> - pr_info("echo %s %s for source %d\n",
> + dev_info(pps->dev, "echo %s %s\n",
> event & PPS_CAPTUREASSERT ? "assert" : "",
> - event & PPS_CAPTURECLEAR ? "clear" : "",
> - source);
> + event & PPS_CAPTURECLEAR ? "clear" : "");
> }
>
> /*
> @@ -84,30 +83,27 @@ static struct pps_source_info pps_ktimer_info = {
>
> static void __exit pps_ktimer_exit(void)
> {
> - del_timer_sync(&ktimer);
> - pps_unregister_source(source);
> + dev_info(pps->dev, "ktimer PPS source unregistered\n");
>
> - pr_info("ktimer PPS source unregistered\n");
> + del_timer_sync(&ktimer);
> + pps_unregister_source(pps);
> }
>
> static int __init pps_ktimer_init(void)
> {
> - int ret;
> -
> - ret = pps_register_source(&pps_ktimer_info,
> + pps = pps_register_source(&pps_ktimer_info,
> PPS_CAPTUREASSERT | PPS_OFFSETASSERT);
> - if (ret < 0) {
> + if (pps == NULL) {
> printk(KERN_ERR "cannot register ktimer source\n");
> - return ret;
> + return -ENOMEM;
> }
> - source = ret;
>
> setup_timer(&ktimer, pps_ktimer_event, 0);
> mod_timer(&ktimer, jiffies + HZ);
>
> - pr_info("ktimer PPS source registered at %d\n", source);
> + dev_info(pps->dev, "ktimer PPS source registered\n");
>
> - return 0;
> + return 0;
> }
>
> module_init(pps_ktimer_init);
> diff --git a/drivers/pps/clients/pps-ldisc.c b/drivers/pps/clients/pps-ldisc.c
> index 20fc9f7..1950b15 100644
> --- a/drivers/pps/clients/pps-ldisc.c
> +++ b/drivers/pps/clients/pps-ldisc.c
> @@ -23,14 +23,18 @@
> #include <linux/serial_core.h>
> #include <linux/tty.h>
> #include <linux/pps_kernel.h>
> +#include <linux/spinlock.h>
>
> #define PPS_TTY_MAGIC 0x0001
>
> +static DEFINE_SPINLOCK(pps_ldisc_lock);
> +
> static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status,
> struct pps_event_time *ts)
> {
> - int id = (long)tty->disc_data;
> + struct pps_device *pps;
> struct pps_event_time __ts;
> + unsigned long flags;
>
> /* First of all we get the time stamp... */
> pps_get_ts(&__ts);
> @@ -39,12 +43,18 @@ static void pps_tty_dcd_change(struct tty_struct *tty, unsigned int status,
> if (!ts) /* No. Do it ourself! */
> ts = &__ts;
>
> - /* Now do the PPS event report */
> - pps_event(id, ts, status ? PPS_CAPTUREASSERT : PPS_CAPTURECLEAR,
> - NULL);
> + spin_lock_irqsave(&pps_ldisc_lock, flags);
>
> - pr_debug("PPS %s at %lu on source #%d\n",
> - status ? "assert" : "clear", jiffies, id);
> + /* Now do the PPS event report */
> + pps = (struct pps_device *)tty->disc_data;
> + if (pps != NULL) {
> + pps_event(pps, ts, status ? PPS_CAPTUREASSERT :
> + PPS_CAPTURECLEAR, NULL);
> + spin_unlock_irqrestore(&pps_ldisc_lock, flags);
> + dev_dbg(pps->dev, "PPS %s at %lu\n",
> + status ? "assert" : "clear", jiffies);

I think you should swap these two lines because after you release the
lock the pps pointer may be not valid...

> + } else
> + spin_unlock_irqrestore(&pps_ldisc_lock, flags);
> }
>
> static int (*alias_n_tty_open)(struct tty_struct *tty);
> @@ -54,7 +64,7 @@ static int pps_tty_open(struct tty_struct *tty)
> struct pps_source_info info;
> struct tty_driver *drv = tty->driver;
> int index = tty->index + drv->name_base;
> - int ret;
> + struct pps_device *pps;
>
> info.owner = THIS_MODULE;
> info.dev = NULL;
> @@ -64,20 +74,22 @@ static int pps_tty_open(struct tty_struct *tty)
> PPS_OFFSETASSERT | PPS_OFFSETCLEAR | \
> PPS_CANWAIT | PPS_TSFMT_TSPEC;
>
> - ret = pps_register_source(&info, PPS_CAPTUREBOTH | \
> + pps = pps_register_source(&info, PPS_CAPTUREBOTH | \
> PPS_OFFSETASSERT | PPS_OFFSETCLEAR);
> - if (ret < 0) {
> + if (pps == NULL) {
> pr_err("cannot register PPS source \"%s\"\n", info.path);
> - return ret;
> + return -ENOMEM;
> }
> - tty->disc_data = (void *)(long)ret;
> +
> + spin_lock_irq(&pps_ldisc_lock);
> + tty->disc_data = pps;
> + spin_unlock_irq(&pps_ldisc_lock);

Maybe this lock is useless... however, are we sure that before setting
tty->disc_data to pps its value is null? Otherwise the dcd_change may
be called with an oops! We cannot control serial port IRQ
generation... :-/

> /* Should open N_TTY ldisc too */
> - ret = alias_n_tty_open(tty);
> - if (ret < 0)
> - pps_unregister_source((long)tty->disc_data);
> + if (alias_n_tty_open(tty) < 0)

Are you sure this code style is «canonical»? What does checkpatch say?
;)

> + pps_unregister_source(pps);

If the above function fails I suppose you should invalidate
tty->disc_data, then unregister the pps source and, in the end, return
error (I know old code returns 0 anywhere, but I think it can be fixed
right now! ;).

> - pr_info("PPS source #%d \"%s\" added\n", ret, info.path);
> + dev_info(pps->dev, "source \"%s\" added\n", info.path);
>
> return 0;
> }
> @@ -86,12 +98,16 @@ static void (*alias_n_tty_close)(struct tty_struct *tty);
>
> static void pps_tty_close(struct tty_struct *tty)
> {
> - int id = (long)tty->disc_data;
> + struct pps_device *pps = (struct pps_device *)tty->disc_data;
>
> - pps_unregister_source(id);
> alias_n_tty_close(tty);
>
> - pr_info("PPS source #%d removed\n", id);
> + spin_lock_irq(&pps_ldisc_lock);
> + tty->disc_data = NULL;
> + spin_unlock_irq(&pps_ldisc_lock);
> +
> + dev_info(pps->dev, "removed\n");
> + pps_unregister_source(pps);
> }
>
> static struct tty_ldisc_ops pps_ldisc_ops;

I suppose you can solve all your problems if you do the lock into
pps_tty_init...

Ciao,

Rodolfo

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