[Nouveau] [PATCH] Take shift in crtc positions for ZaphodHeads configs into account.

Mario Kleiner mario.kleiner.de at gmail.com
Sat Jun 27 17:33:49 PDT 2015

In multi-x-screen ZaphodHeads configurations, there isn't a
one-to-one mapping of kernel provided drmmode crtc index
to the index of the corresponding xf86Crtc inside the
xf86CrtcConfig crtc array anymore, ie. for kernel provided
drmmode->mode_res->crtcs[i], the i'th crtc won't correspond
to the xf86Crtc in the i'th slot of the x-screens xf86CrtcConfig
anymore, once ZaphodHeads has only selected a subset of all crtcs
of a graphics card for a given x-screen, instead of all crtcs.

This breaks the mapping of bit positions in the bit masks returned
in kencoder->possible_crtcs and kencoder->possible_clones. A 1 bit
in position i of those masks allows use of the kernels i'th crtc for
the given kencoder. The X-Servers dix code checks those bit masks
for valid xf86Output -> xf86Crtc assignments, assuming that the i'th
slot xf86CrtcConfigPtr config->crtc[i] corresponds to bit i in the
xf86Output->possibe_crtcs bitmask, and bails if the bitmask doesn't
allow the specified assignment of crtc to output. If ZaphodHeads
breaks the assumption of bit i <-> crtc slot i this ends in failure.

Take this shift of crtc index positions wrt. encoder bitmask bit
positions into account by bit-shifting positions accordingly when
assigning encoder->possible_crtcs to output->possible_crtcs, so
the proper indices match up again for validation by the dix.

This problem wasn't apparent last year when testing the ZaphodHeads
support on some Kepler cards, as apparently the encoder->possible_crtcs
bitmasks returned for those cards by the kernel just had all 4
lsb bits set for all tested encoders/output, so each of the cards 4
crtcs could go with each output and things worked by chance.

The current code breaks, e.g., on 2010 MacBookPro with nv50, where
one crtc is hardwired to the internal lvds panel, and one crtc
is hardwired to the external DP connector, resulting in a failure
where dual-display on single-x-screen works fine, but assigning
each output to a separate x-screen via ZaphodHeads fails due to
the mismatched encoder->possible_crtcs bitmasks.

This patch fixes the problem.

Signed-off-by: Mario Kleiner <mario.kleiner.de at gmail.com>
 src/drmmode_display.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/src/drmmode_display.c b/src/drmmode_display.c
index c30cb3a..3679482 100644
--- a/src/drmmode_display.c
+++ b/src/drmmode_display.c
@@ -1214,7 +1214,7 @@ drmmode_zaphod_match(ScrnInfoPtr pScrn, const char *s, char *output_name)
 static unsigned int
-drmmode_output_init(ScrnInfoPtr pScrn, drmmode_ptr drmmode, int num)
+drmmode_output_init(ScrnInfoPtr pScrn, drmmode_ptr drmmode, int num, int crtcshift)
 	NVPtr pNv = NVPTR(pScrn);
 	xf86OutputPtr output;
@@ -1296,8 +1296,8 @@ drmmode_output_init(ScrnInfoPtr pScrn, drmmode_ptr drmmode, int num)
 	output->subpixel_order = subpixel_conv_table[koutput->subpixel];
 	output->driver_private = drmmode_output;
-	output->possible_crtcs = kencoder->possible_crtcs;
-	output->possible_clones = kencoder->possible_clones;
+	output->possible_crtcs = kencoder->possible_crtcs >> crtcshift;
+	output->possible_clones = kencoder->possible_clones >> crtcshift;
 	output->interlaceAllowed = true;
 	output->doubleScanAllowed = true;
@@ -1421,6 +1421,7 @@ Bool drmmode_pre_init(ScrnInfoPtr pScrn, int fd, int cpp)
 	NVEntPtr pNVEnt = NVEntPriv(pScrn);
 	int i;
 	unsigned int crtcs_needed = 0;
+	int crtcshift;
 	drmmode = xnfalloc(sizeof *drmmode);
 	drmmode->fd = fd;
@@ -1444,8 +1445,9 @@ Bool drmmode_pre_init(ScrnInfoPtr pScrn, int fd, int cpp)
 	xf86DrvMsg(pScrn->scrnIndex, X_INFO, "Initializing outputs ...\n");
+	crtcshift = ffs(pNVEnt->assigned_crtcs ^ 0xffffffff) - 1;
 	for (i = 0; i < drmmode->mode_res->count_connectors; i++)
-		crtcs_needed += drmmode_output_init(pScrn, drmmode, i);
+		crtcs_needed += drmmode_output_init(pScrn, drmmode, i, crtcshift);
 	xf86DrvMsg(pScrn->scrnIndex, X_INFO,
 		   "%d crtcs needed for screen.\n", crtcs_needed);

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