diff options
| author | Maxime Ripard <maxime@cerno.tech> | 2020-11-05 16:56:54 +0300 |
|---|---|---|
| committer | Maxime Ripard <maxime@cerno.tech> | 2020-11-19 16:48:32 +0300 |
| commit | b5dbc4d36885bef6257054a737a76101d293b185 (patch) | |
| tree | d907af43a286a62f32afb437b6af792286865188 /drivers/gpu | |
| parent | a72b0458cd5123b40dd5084f6e536af63aeacda1 (diff) | |
| download | linux-b5dbc4d36885bef6257054a737a76101d293b185.tar.xz | |
drm/vc4: kms: Document the muxing corner cases
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>
Tested-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Reviewed-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20201105135656.383350-6-maxime@cerno.tech
Diffstat (limited to 'drivers/gpu')
| -rw-r--r-- | drivers/gpu/drm/vc4/vc4_kms.c | 22 |
1 files changed, 22 insertions, 0 deletions
diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c index bb2efc5d2d01..0f44fc526fd2 100644 --- a/drivers/gpu/drm/vc4/vc4_kms.c +++ b/drivers/gpu/drm/vc4/vc4_kms.c @@ -662,6 +662,28 @@ static int vc4_load_tracker_obj_init(struct vc4_dev *vc4) return drmm_add_action_or_reset(&vc4->base, vc4_load_tracker_obj_fini, NULL); } +/* + * The BCM2711 HVS has up to 7 outputs 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 pool of available FIFOs. However, there are 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) { |