linux-kernel - [PATCH] drm: via: use ktime_get() instead of do

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Message-Id: <20171104212131.2939989-1-arnd@arndb.de>
Date:   Sat,  4 Nov 2017 22:20:08 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     David Airlie <airlied@...ux.ie>
Cc:     y2038@...ts.linaro.org, Arnd Bergmann <arnd@...db.de>,
        Gabriel Krisman Bertazi <krisman@...labora.co.uk>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Christian König <christian.koenig@....com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH] drm: via: use ktime_get() instead of do_gettimeofday

We want to remove uses of do_gettimeofday() from the kernel since the
resulting timeval structure overflows in 2038. This is not a problem for
this particular use, but do_gettimeofday() is also not an appropriate
method for measuring time intervals, since it requires a conversion into
microseconds and is complicated to work with.

ktime_get() is a better replacement, as it works with the monontonic
kernel timebase and requires a minimum of computation.

I'm slightly changing the output from microseconds to nanoseconds here,
to avoid introducing a new division operation. This should be fine
since the value is only used for debugging.

Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/gpu/drm/via/via_drv.h |  4 ++--
 drivers/gpu/drm/via/via_irq.c | 21 +++++++--------------
 2 files changed, 9 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/via/via_drv.h b/drivers/gpu/drm/via/via_drv.h
index 9873942ca8f4..6d1ae834484c 100644
--- a/drivers/gpu/drm/via/via_drv.h
+++ b/drivers/gpu/drm/via/via_drv.h
@@ -74,9 +74,9 @@ typedef struct drm_via_private {
 	volatile uint32_t *last_pause_ptr;
 	volatile uint32_t *hw_addr_ptr;
 	drm_via_ring_buffer_t ring;
-	struct timeval last_vblank;
+	ktime_t last_vblank;
 	int last_vblank_valid;
-	unsigned usec_per_vblank;
+	ktime_t nsec_per_vblank;
 	atomic_t vbl_received;
 	drm_via_state_t hc_state;
 	char pci_buf[VIA_PCI_BUF_SIZE];
diff --git a/drivers/gpu/drm/via/via_irq.c b/drivers/gpu/drm/via/via_irq.c
index ea8172c747a2..24e71578af4d 100644
--- a/drivers/gpu/drm/via/via_irq.c
+++ b/drivers/gpu/drm/via/via_irq.c
@@ -88,13 +88,6 @@ static int via_num_unichrome = ARRAY_SIZE(via_unichrome_irqs);
 static int via_irqmap_unichrome[] = {-1, -1, -1, 0, -1, 1};
 
 
-static unsigned time_diff(struct timeval *now, struct timeval *then)
-{
-	return (now->tv_usec >= then->tv_usec) ?
-		now->tv_usec - then->tv_usec :
-		1000000 - (then->tv_usec - now->tv_usec);
-}
-
 u32 via_get_vblank_counter(struct drm_device *dev, unsigned int pipe)
 {
 	drm_via_private_t *dev_priv = dev->dev_private;
@@ -111,7 +104,7 @@ irqreturn_t via_driver_irq_handler(int irq, void *arg)
 	drm_via_private_t *dev_priv = (drm_via_private_t *) dev->dev_private;
 	u32 status;
 	int handled = 0;
-	struct timeval cur_vblank;
+	ktime_t cur_vblank;
 	drm_via_irq_t *cur_irq = dev_priv->via_irqs;
 	int i;
 
@@ -119,18 +112,18 @@ irqreturn_t via_driver_irq_handler(int irq, void *arg)
 	if (status & VIA_IRQ_VBLANK_PENDING) {
 		atomic_inc(&dev_priv->vbl_received);
 		if (!(atomic_read(&dev_priv->vbl_received) & 0x0F)) {
-			do_gettimeofday(&cur_vblank);
+			cur_vblank = ktime_get();
 			if (dev_priv->last_vblank_valid) {
-				dev_priv->usec_per_vblank =
-					time_diff(&cur_vblank,
-						  &dev_priv->last_vblank) >> 4;
+				dev_priv->nsec_per_vblank =
+					ktime_sub(cur_vblank,
+						dev_priv->last_vblank) >> 4;
 			}
 			dev_priv->last_vblank = cur_vblank;
 			dev_priv->last_vblank_valid = 1;
 		}
 		if (!(atomic_read(&dev_priv->vbl_received) & 0xFF)) {
-			DRM_DEBUG("US per vblank is: %u\n",
-				  dev_priv->usec_per_vblank);
+			DRM_DEBUG("nsec per vblank is: %llu\n",
+				  ktime_to_ns(dev_priv->nsec_per_vblank));
 		}
 		drm_handle_vblank(dev, 0);
 		handled = 1;
-- 
2.9.0