drm/nouveau: protect evo_wait/evo_kick sections with a channel mutex

With per-crtc locks modeset operations can run in parallel, and the
cursor code uses the device-global evo master channel for hw frobbing.
But the pageflip code can also sync with the master under some
circumstances. Hence just wrap things up in a mutex to ensure that
pushbuf access doesn't intermingle.

The approach here is a bit overkill since the per-crtc channels used
to schedule the pageflips could probably be used without this pushbuf
locking, but I'm not familiar enough with the nouveau codebase to be
sure of that.

v2: Add missing mutex_init to avoid angering lockdep.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
index 3587408..d4cbea1 100644 (file)
--- a/drivers/gpu/drm/nouveau/nv50_display.c
+++ b/drivers/gpu/drm/nouveau/nv50_display.c
@@ -128,6 +128,11 @@ struct nv50_dmac {
        struct nv50_chan base;
        dma_addr_t handle;
        u32 *ptr;
+
+       /* Protects against concurrent pushbuf access to this channel, lock is
+        * grabbed by evo_wait (if the pushbuf reservation is successful) and
+        * dropped again by evo_kick. */
+       struct mutex lock;
 };
 
 static void
@@ -271,6 +276,8 @@ nv50_dmac_create(struct nouveau_object *core, u32 bclass, u8 head,
        u32 pushbuf = *(u32 *)data;
        int ret;
 
+       mutex_init(&dmac->lock);
+
        dmac->ptr = pci_alloc_consistent(nv_device(core)->pdev, PAGE_SIZE,
                                        &dmac->handle);
        if (!dmac->ptr)
@@ -395,11 +402,13 @@ evo_wait(void *evoc, int nr)
        struct nv50_dmac *dmac = evoc;
        u32 put = nv_ro32(dmac->base.user, 0x0000) / 4;
 
+       mutex_lock(&dmac->lock);
        if (put + nr >= (PAGE_SIZE / 4) - 8) {
                dmac->ptr[put] = 0x20000000;
 
                nv_wo32(dmac->base.user, 0x0000, 0x00000000);
                if (!nv_wait(dmac->base.user, 0x0004, ~0, 0x00000000)) {
+                       mutex_unlock(&dmac->lock);
                        NV_ERROR(dmac->base.user, "channel stalled\n");
                        return NULL;
                }
@@ -415,6 +424,7 @@ evo_kick(u32 *push, void *evoc)
 {
        struct nv50_dmac *dmac = evoc;
        nv_wo32(dmac->base.user, 0x0000, (push - dmac->ptr) << 2);
+       mutex_unlock(&dmac->lock);
 }
 
 #define evo_mthd(p,m,s) *((p)++) = (((s) << 18) | (m))