On Tue, Oct 29, 2019 at 7:49 AM Christoph Hellwig [off-list ref] wrote:

Whatever reason there is for the existence of ioremap_uc, and the fact
that it returns NULL by default on architectures with an MMU applies
equally to nommu architectures, so don't provide different defaults.

Makes sense.

In practice the difference is meaningless as the only portable driver
that uses ioremap_uc is atyfb which probably doesn't show up on nommu
devices.

+/*
+ * ioremap_uc is special in that we do require an explicit architecture
+ * implementation.  In general you do now want to use this function in a
+ * driver and use plain ioremap, which is uncached by default.  Similarly
+ * architectures should not implement it unless they have a very good
+ * reason.
+ */
+#ifndef ioremap_uc
+#define ioremap_uc ioremap_uc
+static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
+{
+       return NULL;
+}
+#endif

Maybe we could move the definition into the atyfb driver itself?

As I understand it, the difference between ioremap()/ioremap_nocache()
and ioremap_uc() only exists on pre-PAT x86-32 systems (i.e. 486, P5,
Ppro, PII, K6, VIA C3), while on more modern systems (all non-x86,
PentiumIII, Athlon, VIA C7)  those three are meant to be synonyms
anyway.

      Arnd