drm/etnaviv: fix external abort seen on GC600 rev 0x19

It looks like that this GPU core triggers an abort when
reading VIVS_HI_CHIP_PRODUCT_ID and/or VIVS_HI_CHIP_ECO_ID.

I looked at different versions of Vivante's kernel driver and did
not found anything about this issue or what feature flag can be
used. So go the simplest route and do not read these two registers
on the affected GPU core.
Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reported-by: Josua Mayer <josua.mayer@jm0.eu>
Fixes: 815e45bb ("drm/etnaviv: determine product, customer and eco id")
Cc: stable@vger.kernel.org
Tested-by: Josua Mayer <josua.mayer@jm0.eu>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>

drivers/gpu/drm/etnaviv/etnaviv_gpu.c

@@ -337,9 +337,16 @@ static void etnaviv_hw_identify(struct etnaviv_gpu *gpu)
 
 		gpu->identity.model = gpu_read(gpu, VIVS_HI_CHIP_MODEL);
 		gpu->identity.revision = gpu_read(gpu, VIVS_HI_CHIP_REV);
-		gpu->identity.product_id = gpu_read(gpu, VIVS_HI_CHIP_PRODUCT_ID);
 		gpu->identity.customer_id = gpu_read(gpu, VIVS_HI_CHIP_CUSTOMER_ID);
+
+		/*
+		 * Reading these two registers on GC600 rev 0x19 result in a
+		 * unhandled fault: external abort on non-linefetch
+		 */
+		if (!etnaviv_is_model_rev(gpu, GC600, 0x19)) {
+			gpu->identity.product_id = gpu_read(gpu, VIVS_HI_CHIP_PRODUCT_ID);
 			gpu->identity.eco_id = gpu_read(gpu, VIVS_HI_CHIP_ECO_ID);
+		}
 
 		/*
 		 * !!!! HACK ALERT !!!!