[RFC PATCH] drm: disable WC optimization for cache coherent devices on non-x86

[Christoph Hellwig]

> +#include <linux/dma-noncoherent.h>

This header is not for usage in device drivers, but purely for
dma-mapping implementations!

> +static inline bool drm_device_can_wc_memory(struct drm_device *ddev)
>  {
> +	if (IS_ENABLED(CONFIG_PPC))
> +		return IS_ENABLED(CONFIG_NOT_COHERENT_CACHE);
> +	else if (IS_ENABLED(CONFIG_MIPS))
> +		return !IS_ENABLED(CONFIG_CPU_LOONGSON3);
> +	else if (IS_ENABLED(CONFIG_X86))
> +		return true;
> +
> +	return !dev_is_dma_coherent(ddev->dev);

And even if something like this was valid to do, it would have to be
a core function with an arch hook, and not hidden in a random driver.