drm/msm/adreno: fix zap vs no-zap handling

We can have two cases, when it comes to "zap" fw.  Either the fw
requires zap fw to take the GPU out of secure mode at boot, or it does
not and we can write RBBM_SECVID_TRUST_CNTL directly.  Previously we
decided based on whether zap fw load succeeded, but this is not a great
plan because:

1) we could have zap fw in the filesystem on a device where it is not
   required
2) we could have the inverse case

Instead, shift to deciding based on whether we have a 'zap-shader' node
in dt.  In practice, there is only one device (currently) with upstream
dt that does not use zap (cheza), and it already has a /delete-node/ for
the zap-shader node.

Fixes: abccb9fe ("drm/msm/a6xx: Add zap shader load")
Signed-off-by: Rob Clark <robdclark@chromium.org>

drivers/gpu/drm/msm/adreno/a5xx_gpu.c

@@ -753,11 +753,18 @@ static int a5xx_hw_init(struct msm_gpu *gpu)
 		gpu->funcs->flush(gpu, gpu->rb[0]);
 		if (!a5xx_idle(gpu, gpu->rb[0]))
 			return -EINVAL;
-	} else {
-		/* Print a warning so if we die, we know why */
+	} else if (ret == -ENODEV) {
+		/*
+		 * This device does not use zap shader (but print a warning
+		 * just in case someone got their dt wrong.. hopefully they
+		 * have a debug UART to realize the error of their ways...
+		 * if you mess this up you are about to crash horribly)
+		 */
 		dev_warn_once(gpu->dev->dev,
 			"Zap shader not enabled - using SECVID_TRUST_CNTL instead\n");
 		gpu_write(gpu, REG_A5XX_RBBM_SECVID_TRUST_CNTL, 0x0);
+	} else {
+		return ret;
 	}
 
 	/* Last step - yield the ringbuffer */

drivers/gpu/drm/msm/adreno/a6xx_gpu.c

@@ -537,12 +537,19 @@ static int a6xx_hw_init(struct msm_gpu *gpu)
 		a6xx_flush(gpu, gpu->rb[0]);
 		if (!a6xx_idle(gpu, gpu->rb[0]))
 			return -EINVAL;
-	} else {
-		/* Print a warning so if we die, we know why */
+	} else if (ret == -ENODEV) {
+		/*
+		 * This device does not use zap shader (but print a warning
+		 * just in case someone got their dt wrong.. hopefully they
+		 * have a debug UART to realize the error of their ways...
+		 * if you mess this up you are about to crash horribly)
+		 */
 		dev_warn_once(gpu->dev->dev,
 			"Zap shader not enabled - using SECVID_TRUST_CNTL instead\n");
 		gpu_write(gpu, REG_A6XX_RBBM_SECVID_TRUST_CNTL, 0x0);
 		ret = 0;
+	} else {
+		return ret;
 	}
 
 out: