[PATCH 9/9] drm/ttm: Sanity check mapping attributes on powerpc in ttm_io_prot()

[Michel Dänzer]

On 04.09.2014 16:47, Benjamin Herrenschmidt wrote:
> On all current cache coherent powerpc processors, it is not legit
> to map system memory non-cachable. This will cause aliases with
> the linear mapping which can be fatal.
>
> The TTM should generally avoid it after Jerome placement patches but
> let's add a sanity check anyway to catch any possible remaining issue.
>
> Signed-off-by: Benjamin Herrenschmidt <benh at palm4.ozlabs.ibm.com>

[...]

> @@ -498,6 +501,20 @@ pgprot_t ttm_io_prot(uint32_t caching_flags, pgprot_t tmp)
>   		tmp = pgprot_noncached(tmp);
>
>   #endif
> +#if defined(__powerpc__) && !defined(CONFIG_NOT_COHERENT_CACHE)
> +	/*
> +	 * Using a non-cachable mapping of system memory on
> +	 * cache coherent powerpc's can be fatal, let's make
> +	 * sure this doesn't happen and warn if it does. The
> +	 * only exception is powermac with AGP which has to
> +	 * take the risk.
> +	 */
> +	if (!machine_is(powermac) &&
> +	    ((caching_flags & TTM_PL_FLAG_SYSTEM) ||
> +	     (caching_flags & TTM_PL_FLAG_TT))) {
> +		pr_err_once("TTM: Attempt to use a non-cached"
> +			    " mapping on RAM unsupported !\n");
> +		return tmp;

NAK, this breaks AGP on PowerMacs.


-- 
Earthling Michel Dänzer            |                  http://www.amd.com
Libre software enthusiast          |                Mesa and X developer