drm/etnaviv: make THERMAL selectable

The etnaviv driver causes a link failure if it is built-in but THERMAL
is built as a module:

drivers/gpu/drm/etnaviv/etnaviv_gpu.o: In function `etnaviv_gpu_bind':
etnaviv_gpu.c:(.text+0x4c4): undefined reference to `thermal_of_cooling_device_register'
etnaviv_gpu.c:(.text+0x600): undefined reference to `thermal_cooling_device_unregister'
drivers/gpu/drm/etnaviv/etnaviv_gpu.o: In function `etnaviv_gpu_unbind':
etnaviv_gpu.c:(.text+0x2aac): undefined reference to `thermal_cooling_device_unregister'

Adding a Kconfig dependency on THERMAL || !THERMAL to avoid this causes
a dependency loop on x86_64:

drivers/gpu/drm/tve200/Kconfig:1:error: recursive dependency detected!
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/gpu/drm/tve200/Kconfig:1: symbol DRM_TVE200 depends on CMA
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
mm/Kconfig:489: symbol CMA is selected by DRM_ETNAVIV
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/gpu/drm/etnaviv/Kconfig:2: symbol DRM_ETNAVIV depends on THERMAL
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/thermal/Kconfig:5: symbol THERMAL is selected by ACPI_VIDEO
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/acpi/Kconfig:189: symbol ACPI_VIDEO is selected by BACKLIGHT_CLASS_DEVICE
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/video/backlight/Kconfig:158: symbol BACKLIGHT_CLASS_DEVICE is selected by DRM_PARADE_PS8622
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/gpu/drm/bridge/Kconfig:62: symbol DRM_PARADE_PS8622 depends on DRM_BRIDGE
For a resolution refer to Documentation/kbuild/kconfig-language.txt
subsection "Kconfig recursive dependency limitations"
drivers/gpu/drm/bridge/Kconfig:1: symbol DRM_BRIDGE is selected by DRM_TVE200

To work around this, add a new option DRM_ETNAVIV_THERMAL to optionally
enable thermal throttling support and make DRM_ETNAVIV select THERMAL
at the same time.

Reported-by: Stephen Rothwell <[e-mail]>
Signed-off-by: Philipp Zabel <[e-mail]>
Signed-off-by: Lucas Stach <[e-mail]>

drivers/gpu/drm/etnaviv/Kconfig

···
 	depends on MMU
 	select SHMEM
 	select SYNC_FILE
+	select THERMAL if DRM_ETNAVIV_THERMAL
 	select TMPFS
 	select WANT_DEV_COREDUMP
 	select CMA if HAVE_DMA_CONTIGUOUS
 	select DMA_CMA if HAVE_DMA_CONTIGUOUS
 	help
 	  DRM driver for Vivante GPUs.
+
+config DRM_ETNAVIV_THERMAL
+	bool "enable ETNAVIV thermal throttling"
+	depends on DRM_ETNAVIV
+	default y
+	help
+	  Compile in support for thermal throttling.
+	  Say Y unless you want to risk burning your SoC.
 
 config DRM_ETNAVIV_REGISTER_LOGGING
 	bool "enable ETNAVIV register logging"

drivers/gpu/drm/etnaviv/etnaviv_gpu.c

···
 	struct etnaviv_gpu *gpu = dev_get_drvdata(dev);
 	int ret;
 
-	if (IS_ENABLED(CONFIG_THERMAL)) {
+	if (IS_ENABLED(CONFIG_DRM_ETNAVIV_THERMAL)) {
 		gpu->cooling = thermal_of_cooling_device_register(dev->of_node,
 				(char *)dev_name(dev), gpu, &cooling_ops);
 		if (IS_ERR(gpu->cooling))
···
 	ret = etnaviv_gpu_clk_enable(gpu);
 #endif
 	if (ret < 0) {
-		thermal_cooling_device_unregister(gpu->cooling);
+		if (IS_ENABLED(CONFIG_DRM_ETNAVIV_THERMAL))
+			thermal_cooling_device_unregister(gpu->cooling);
 		return ret;
 	}
 
···
 
 	gpu->drm = NULL;
 
-	thermal_cooling_device_unregister(gpu->cooling);
+	if (IS_ENABLED(CONFIG_DRM_ETNAVIV_THERMAL))
+		thermal_cooling_device_unregister(gpu->cooling);
 	gpu->cooling = NULL;
 }