linux-kernel - Re: [PATCH] staging: gasket remove current_kernel

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Message-ID: <20180713154617.GA24618@kroah.com>
Date:   Fri, 13 Jul 2018 17:46:17 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     devel@...verdev.osuosl.org, John Joseph <jnjoseph@...gle.com>,
        linux-kernel@...r.kernel.org, Simon Que <sque@...omium.org>,
        Rob Springer <rspringer@...gle.com>
Subject: Re: [PATCH] staging: gasket remove current_kernel_time usage

On Fri, Jul 13, 2018 at 05:33:51PM +0200, Greg Kroah-Hartman wrote:
> On Fri, Jul 13, 2018 at 05:06:37PM +0200, Arnd Bergmann wrote:
> > A new user of the deprecated current_kernel_time() function has appeared
> > here. This code won't work correct during leap seconds or a concurrent
> > settimeofday() call, and it probably doesn't do what the author intended
> > even for the normal case, as it passes a timeout in nanoseconds but
> > reads the time using a jiffies-granularity accessor.
> > 
> > I'm changing it to ktime_get_ns() here, which simplifies the logic,
> > and uses a high-res clocksource. This is a bit slower, but that
> > probably doesn't matter in a busy-wait loop.
> > 
> > Note: it also doesn't matter in the current version, as there are no
> > callers of this function.
> 
> Let's just rip the whole function out, I've been going through and
> removing functions that no one calls and no one uses.  That would make
> more sense here.  Want me to send a patch for that, or do you want to?

Ah it was easy enough, here's the patch, I'll add it to the longer list
of gasket patches I have queued up to be applied tomorrow:

-------------

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH] staging: gasket: remove gasket_wait_sync()

This function is not called anywhere, so just remove it.

Also, as an added benifit, Arnd points out that it doesn't even work
properly:
	This code won't work correct during leap seconds or a concurrent
	settimeofday() call, and it probably doesn't do what the author intended
	even for the normal case, as it passes a timeout in nanoseconds but
	reads the time using a jiffies-granularity accessor.

Reported-by: Arnd Bergmann <arnd@...db.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>


diff --git a/drivers/staging/gasket/gasket_core.c b/drivers/staging/gasket/gasket_core.c
index 4ca6e53116ea..df52e6e6bf13 100644
--- a/drivers/staging/gasket/gasket_core.c
+++ b/drivers/staging/gasket/gasket_core.c
@@ -2067,50 +2067,6 @@ struct device *gasket_get_device(struct gasket_dev *dev)
 	return NULL;
 }
 
-/**
- * Synchronously waits on device.
- * @gasket_dev: Device struct.
- * @bar: Bar
- * @offset: Register offset
- * @mask: Register mask
- * @val: Expected value
- * @timeout_ns: Timeout in nanoseconds
- *
- * Description: Busy waits for a specific combination of bits to be set
- * on a Gasket register.
- **/
-int gasket_wait_sync(
-	struct gasket_dev *gasket_dev, int bar, u64 offset, u64 mask, u64 val,
-	u64 timeout_ns)
-{
-	u64 reg;
-	struct timespec start_time, cur_time;
-	u64 diff_nanosec;
-	int count = 0;
-
-	reg = gasket_dev_read_64(gasket_dev, bar, offset);
-	start_time = current_kernel_time();
-	while ((reg & mask) != val) {
-		count++;
-		cur_time = current_kernel_time();
-		diff_nanosec = (u64)(cur_time.tv_sec - start_time.tv_sec) *
-				       1000000000LL +
-			       (u64)(cur_time.tv_nsec) -
-			       (u64)(start_time.tv_nsec);
-		if (diff_nanosec > timeout_ns) {
-			gasket_log_error(
-				gasket_dev,
-				"gasket_wait_sync timeout: reg %llx count %x "
-				"dma %lld ns\n",
-				offset, count, diff_nanosec);
-			return -1;
-		}
-		reg = gasket_dev_read_64(gasket_dev, bar, offset);
-	}
-	return 0;
-}
-EXPORT_SYMBOL(gasket_wait_sync);
-
 /**
  * Asynchronously waits on device.
  * @gasket_dev: Device struct.
diff --git a/drivers/staging/gasket/gasket_core.h b/drivers/staging/gasket/gasket_core.h
index 45013446b8c5..e51acadc0fc4 100644
--- a/drivers/staging/gasket/gasket_core.h
+++ b/drivers/staging/gasket/gasket_core.h
@@ -699,11 +699,6 @@ const struct gasket_driver_desc *gasket_get_driver_desc(struct gasket_dev *dev);
 /* Get the device structure for a given device. */
 struct device *gasket_get_device(struct gasket_dev *dev);
 
-/* Helper function, Synchronous waits on a given set of bits. */
-int gasket_wait_sync(
-	struct gasket_dev *gasket_dev, int bar, u64 offset, u64 mask, u64 val,
-	u64 timeout_ns);
-
 /* Helper function, Asynchronous waits on a given set of bits. */
 int gasket_wait_with_reschedule(
 	struct gasket_dev *gasket_dev, int bar, u64 offset, u64 mask, u64 val,