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@xxxxxxxxxxxxxxxxxxxx>
[...]
@@ -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
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