[Intel-gfx] [PATCH 13/13] drm/i915: Add i915.nuclear kernel command line param to force atomic

[Matt Roper]

We don't have full atomic modeset support yet, but the "nuclear
pageflip" subset of functionality (i.e., plane operations only) should
be ready.  Allow the user to force atomic on for debug purposes, or for
fixed-purpose embedded devices that will only use atomic for plane
updates.

The term 'nuclear' is used here instead of 'atomic' to make it clear
that this doesn't allow full atomic modeset support, just a (very
useful) subset of the atomic functionality.

We'll drop the kernel parameter and unconditionally enable atomic in a
future patch once all of the necessary pieces are in.

Signed-off-by: Matt Roper <matthew.d.roper at intel.com>
---
 drivers/gpu/drm/i915/i915_drv.c    | 12 ++++++++++++
 drivers/gpu/drm/i915/i915_drv.h    |  1 +
 drivers/gpu/drm/i915/i915_params.c |  5 +++++
 3 files changed, 18 insertions(+)

diff --git a/drivers/gpu/drm/i915/i915_drv.c b/drivers/gpu/drm/i915/i915_drv.c
index 308774f..173747a 100644
--- a/drivers/gpu/drm/i915/i915_drv.c
+++ b/drivers/gpu/drm/i915/i915_drv.c
@@ -1642,6 +1642,18 @@ static int __init i915_init(void)
 #endif
 	}
 
+	/*
+	 * FIXME: We don't yet support full atomic modeset, just the plane
+	 * operations subset (i.e., the "nuclear pageflip" functionality).
+	 * Allow us to advertise atomic functionality when specifically
+	 * requested on the kernel command line.
+	 *
+	 * We'll remove this module parameter and just advertise DRIVER_ATOMIC
+	 * unconditionally once the rest of the atomic infrastructure is ready.
+	 */
+	if (i915.nuclear)
+		driver.driver_features |= DRIVER_ATOMIC;
+
 	return drm_pci_init(&driver, &i915_pci_driver);
 }
 
diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 1d55c94..b53564b 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -2445,6 +2445,7 @@ struct i915_params {
 	int use_mmio_flip;
 	bool mmio_debug;
 	bool verbose_state_checks;
+	bool nuclear;
 };
 extern struct i915_params i915 __read_mostly;
 
diff --git a/drivers/gpu/drm/i915/i915_params.c b/drivers/gpu/drm/i915/i915_params.c
index 07252d8..54ea182 100644
--- a/drivers/gpu/drm/i915/i915_params.c
+++ b/drivers/gpu/drm/i915/i915_params.c
@@ -52,6 +52,7 @@ struct i915_params i915 __read_mostly = {
 	.use_mmio_flip = 0,
 	.mmio_debug = 0,
 	.verbose_state_checks = 1,
+	.nuclear = 0,
 };
 
 module_param_named(modeset, i915.modeset, int, 0400);
@@ -178,3 +179,7 @@ MODULE_PARM_DESC(mmio_debug,
 module_param_named(verbose_state_checks, i915.verbose_state_checks, bool, 0600);
 MODULE_PARM_DESC(verbose_state_checks,
 	"Enable verbose logs (ie. WARN_ON()) in case of unexpected hw state conditions.");
+
+module_param_named(nuclear, i915.nuclear, bool, 0600);
+MODULE_PARM_DESC(nuclear,
+		 "Force atomic modeset functionality; only planes work for now (default: false).");
-- 
1.8.5.1