Re: [PATCH v3 04/27] drm: Don't test for IRQ support in VBLANK ioctls

On Thu, Jun 24, 2021 at 11:07:57AM +0200, Thomas Zimmermann wrote:

Hi

Am 24.06.21 um 10:51 schrieb Jani Nikula:

quoted

On Thu, 24 Jun 2021, Thomas Zimmermann [off-list ref] wrote:

quoted

Hi

Am 24.06.21 um 10:06 schrieb Jani Nikula:

quoted

On Thu, 24 Jun 2021, Thomas Zimmermann [off-list ref] wrote:

quoted

diff --git a/drivers/gpu/drm/drm_vblank.c b/drivers/gpu/drm/drm_vblank.c
index 3417e1ac7918..10fe16bafcb6 100644
--- a/drivers/gpu/drm/drm_vblank.c
+++ b/drivers/gpu/drm/drm_vblank.c

@@ -1748,8 +1748,16 @@ int drm_wait_vblank_ioctl(struct drm_device *dev, void *data,
   	unsigned int pipe_index;
   	unsigned int flags, pipe, high_pipe;
-	if (!dev->irq_enabled)
-		return -EOPNOTSUPP;
+#if defined(CONFIG_DRM_LEGACY)
+	if  (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY))) {
+		if (!dev->irq_enabled)
+			return -EOPNOTSUPP;
+	} else /* if DRIVER_MODESET */
+#endif
+	{
+		if (!drm_dev_has_vblank(dev))
+			return -EOPNOTSUPP;
+	}

Sheesh I hate this kind of inline #ifdefs.

Two alternate suggestions that I believe should be as just efficient:

Or how about:

static bool drm_wait_vblank_supported(struct drm_device *dev)

{

if defined(CONFIG_DRM_LEGACY)
	if  (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)))

		return dev->irq_enabled;

#endif
	return drm_dev_has_vblank(dev);

}


?

It's inline, but still readable.

It's definitely better than the original, but it's unclear to me why
you'd prefer this over option 2) below. I guess the only reason I can
think of is emphasizing the conditional compilation. However,
IS_ENABLED() is widely used in this manner specifically to avoid inline
#if, and the compiler optimizes it away.

It's simply more readable to me as the condition is simpler. But option 2 is
also ok.

Perhaps do something like this, then:

	if (IS_ENABLED(CONFIG_DRM_LEGACY)) {
		if (unlikely(drm_core_check_feature(dev, DRIVER_LEGACY)))
			return dev->irq_enabled;
	}

	return drm_dev_has_vblank(dev);

That's about just as readable as the variant involving the preprocessor
but has all the benefits of not using the preprocessor.

Thierry