drm/v3d: Address race-condition in MMU flush

We must first flush the MMU cache and then, flush the TLB, not the other
way around. Currently, we can see a race condition between the MMU cache
and the TLB when running multiple rendering processes at the same time.
This is evidenced by MMU errors triggered by the IRQ.

Fix the MMU flush order by flushing the MMU cache and then the TLB.
Also, in order to address the race condition, wait for the MMU cache flush
to finish before starting the TLB flush.

Fixes: 57692c94dcbe ("drm/v3d: Introduce a new DRM driver for Broadcom V3D V3.x+")
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240923141348.2422499-2-mcanal@igalia.com

diff --git a/drivers/gpu/drm/v3d/v3d_mmu.c b/drivers/gpu/drm/v3d/v3d_mmu.c
index 14f3af40d6f6d16ebd9863c12519959e88be17fd..e36ec3343b06ea0f5e355a276caa687552054904 100644 (file)
--- a/drivers/gpu/drm/v3d/v3d_mmu.c
+++ b/drivers/gpu/drm/v3d/v3d_mmu.c
@@ -32,32 +32,23 @@ static int v3d_mmu_flush_all(struct v3d_dev *v3d)
 {
        int ret;
 
-       /* Make sure that another flush isn't already running when we
-        * start this one.
-        */
-       ret = wait_for(!(V3D_READ(V3D_MMU_CTL) &
-                        V3D_MMU_CTL_TLB_CLEARING), 100);
-       if (ret)
-               dev_err(v3d->drm.dev, "TLB clear wait idle pre-wait failed\n");
-
-       V3D_WRITE(V3D_MMU_CTL, V3D_READ(V3D_MMU_CTL) |
-                 V3D_MMU_CTL_TLB_CLEAR);
-
-       V3D_WRITE(V3D_MMUC_CONTROL,
-                 V3D_MMUC_CONTROL_FLUSH |
+       V3D_WRITE(V3D_MMUC_CONTROL, V3D_MMUC_CONTROL_FLUSH |
                  V3D_MMUC_CONTROL_ENABLE);
 
-       ret = wait_for(!(V3D_READ(V3D_MMU_CTL) &
-                        V3D_MMU_CTL_TLB_CLEARING), 100);
+       ret = wait_for(!(V3D_READ(V3D_MMUC_CONTROL) &
+                        V3D_MMUC_CONTROL_FLUSHING), 100);
        if (ret) {
-               dev_err(v3d->drm.dev, "TLB clear wait idle failed\n");
+               dev_err(v3d->drm.dev, "MMUC flush wait idle failed\n");
                return ret;
        }
 
-       ret = wait_for(!(V3D_READ(V3D_MMUC_CONTROL) &
-                        V3D_MMUC_CONTROL_FLUSHING), 100);
+       V3D_WRITE(V3D_MMU_CTL, V3D_READ(V3D_MMU_CTL) |
+                 V3D_MMU_CTL_TLB_CLEAR);
+
+       ret = wait_for(!(V3D_READ(V3D_MMU_CTL) &
+                        V3D_MMU_CTL_TLB_CLEARING), 100);
        if (ret)
-               dev_err(v3d->drm.dev, "MMUC flush wait idle failed\n");
+               dev_err(v3d->drm.dev, "MMU TLB clear wait idle failed\n");
 
        return ret;
 }