From: Maxime Ripard <maxime@cerno.tech>
To: Mark Rutland <mark.rutland@arm.com>,
Rob Herring <robh+dt@kernel.org>,
Frank Rowand <frowand.list@gmail.com>,
Daniel Vetter <daniel.vetter@intel.com>,
David Airlie <airlied@linux.ie>,
Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
Thomas Zimmermann <tzimmermann@suse.de>,
Maxime Ripard <maxime@cerno.tech>, Eric Anholt <eric@anholt.net>
Cc: devicetree@vger.kernel.org, Tim Gover <tim.gover@raspberrypi.com>,
Dave Stevenson <dave.stevenson@raspberrypi.com>,
dri-devel@lists.freedesktop.org,
Hoegeun Kwon <hoegeun.kwon@samsung.com>,
bcm-kernel-feedback-list@broadcom.com,
linux-rpi-kernel@lists.infradead.org,
Phil Elwell <phil@raspberrypi.com>,
linux-arm-kernel@lists.infradead.org
Subject: [PATCH 2/4] drm/vc4: kms: Document the muxing corner cases
Date: Thu, 8 Oct 2020 13:25:17 +0200 [thread overview]
Message-ID: <20201008112519.43691-2-maxime@cerno.tech> (raw)
In-Reply-To: <20201008112519.43691-1-maxime@cerno.tech>
We've had a number of muxing corner-cases with specific ways to reproduce
them, so let's document them to make sure they aren't lost and introduce
regressions later on.
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
drivers/gpu/drm/vc4/vc4_kms.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 846fe8b3cb7a..3b5e62842901 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -612,6 +612,28 @@ static const struct drm_private_state_funcs vc4_load_tracker_state_funcs = {
#define NUM_OUTPUTS 6
#define NUM_CHANNELS 3
+/*
+ * The BCM2711 HVS has up to 7 output connected to the pixelvalves and
+ * the TXP (and therefore all the CRTCs found on that platform).
+ *
+ * The naive (and our initial) implementation would just iterate over
+ * all the active CRTCs, try to find a suitable FIFO, and then remove it
+ * from the available FIFOs pool. However, there's a few corner cases
+ * that need to be considered:
+ *
+ * - When running in a dual-display setup (so with two CRTCs involved),
+ * we can update the state of a single CRTC (for example by changing
+ * its mode using xrandr under X11) without affecting the other. In
+ * this case, the other CRTC wouldn't be in the state at all, so we
+ * need to consider all the running CRTCs in the DRM device to assign
+ * a FIFO, not just the one in the state.
+ *
+ * - Since we need the pixelvalve to be disabled and enabled back when
+ * the FIFO is changed, we should keep the FIFO assigned for as long
+ * as the CRTC is enabled, only considering it free again once that
+ * CRTC has been disabled. This can be tested by booting X11 on a
+ * single display, and changing the resolution down and then back up.
+ */
static int vc4_pv_muxing_atomic_check(struct drm_device *dev,
struct drm_atomic_state *state)
{
--
2.26.2
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next prev parent reply other threads:[~2020-10-09 7:31 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <CGME20201008112530epcas1p30d837c7b03283651c988a2177558e376@epcas1p3.samsung.com>
2020-10-08 11:25 ` [PATCH 1/4] drm/vc4: kms: Split the HVS muxing check in a separate function Maxime Ripard
2020-10-08 11:25 ` Maxime Ripard [this message]
2020-10-08 11:25 ` [PATCH 3/4] drm/vc4: kms: Don't disable the muxing of an active CRTC Maxime Ripard
2020-10-08 11:25 ` [PATCH 4/4] drm/vc4: kms: Fix VBLANK reporting on a disabled CRTC Maxime Ripard
2020-10-12 12:25 ` [PATCH 1/4] drm/vc4: kms: Split the HVS muxing check in a separate function Hoegeun Kwon
2020-10-19 10:21 ` Maxime Ripard
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