[PATCH 3/8] kconfig: turn PDX compression into a choice

[Roger Pau Monne <roger.pau@xxxxxxxxxx>]

Rename the current CONFIG_PDX_COMPRESSION to CONFIG_PDX_MASK_COMPRESSION,
and make it part of the PDX compression choice block, in preparation for
adding further PDX compression algorithms.

No functional change intended as the PDX compression defaults should still
be the same for all architectures, however the choice block cannot be
protected under EXPERT and still have a default choice being
unconditionally selected.  As a result, the new "PDX (Page inDeX)
compression" item will be unconditionally visible in Kconfig.

As part of this preparation work to introduce new PDX compressions, adjust
some of the comments on pdx.h to note they apply to a specific PDX
compression.  Also shuffle function prototypes and dummy implementations
around to make it easier to introduce a new PDX compression.  Note all
PDX compression implementations are expected to provide a
pdx_is_region_compressible() that takes the same set of arguments.

Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
---
 xen/common/Kconfig    | 18 +++++++++++++++---
 xen/common/pdx.c      |  4 ++--
 xen/include/xen/pdx.h | 32 +++++++++++++++++++-------------
 3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/xen/common/Kconfig b/xen/common/Kconfig
index eece1370a3cc..7ffd9d7d9003 100644
--- a/xen/common/Kconfig
+++ b/xen/common/Kconfig
@@ -52,9 +52,10 @@ config EVTCHN_FIFO
 
          If unsure, say Y.
 
-config PDX_COMPRESSION
-       bool "PDX (Page inDeX) compression" if EXPERT && !X86 && !RISCV
-       default ARM || PPC
+choice
+       prompt "PDX (Page inDeX) compression"
+       default PDX_MASK_COMPRESSION if !X86 && !RISCV
+       default PDX_NONE
        help
          PDX compression is a technique designed to reduce the memory
          overhead of physical memory management on platforms with sparse RAM
@@ -67,6 +68,17 @@ config PDX_COMPRESSION
          If your platform does not have sparse RAM banks, do not enable PDX
          compression.
 
+config PDX_MASK_COMPRESSION
+       bool "Mask compression"
+       help
+         Compression relying on all RAM addresses sharing a zeroed bit region.
+
+config PDX_NONE
+       bool "None"
+       help
+         No compression
+endchoice
+
 config ALTERNATIVE_CALL
        bool
 
diff --git a/xen/common/pdx.c b/xen/common/pdx.c
index 3004c5f28bdd..4843630bee7f 100644
--- a/xen/common/pdx.c
+++ b/xen/common/pdx.c
@@ -34,7 +34,7 @@ bool __mfn_valid(unsigned long mfn)
 {
     bool invalid = mfn >= max_page;
 
-#ifdef CONFIG_PDX_COMPRESSION
+#ifdef CONFIG_PDX_MASK_COMPRESSION
     invalid |= mfn & pfn_hole_mask;
 #endif
 
@@ -80,7 +80,7 @@ unsigned long get_max_pfn(unsigned long top_pfn)
     return pdx_to_pfn(pdx - 1) + 1;
 }
 
-#ifdef CONFIG_PDX_COMPRESSION
+#ifdef CONFIG_PDX_MASK_COMPRESSION
 
 /*
  * Diagram to make sense of the following variables. The masks and shifts
diff --git a/xen/include/xen/pdx.h b/xen/include/xen/pdx.h
index 0f580853cb2e..ec0827936c2f 100644
--- a/xen/include/xen/pdx.h
+++ b/xen/include/xen/pdx.h
@@ -25,7 +25,7 @@
  * this by keeping a bitmap of the ranges in the frame table containing
  * invalid entries and not allocating backing memory for them.
  *
- * ## PDX compression
+ * ## PDX mask compression
  *
  * This is a technique to avoid wasting memory on machines known to have
  * split their machine address space in several big discontinuous and highly
@@ -108,22 +108,13 @@ unsigned long get_max_pfn(unsigned long top_pfn);
 
 #define paddr_to_pdx(pa) pfn_to_pdx(paddr_to_pfn(pa))
 
-#ifdef CONFIG_PDX_COMPRESSION
+#ifdef CONFIG_PDX_MASK_COMPRESSION
 
 extern unsigned long pfn_pdx_bottom_mask, ma_va_bottom_mask;
 extern unsigned int pfn_pdx_hole_shift;
 extern unsigned long pfn_hole_mask;
 extern unsigned long pfn_top_mask, ma_top_mask;
 
-/**
- * Validate a region's compatibility with the current compression runtime
- *
- * @param base Base address of the region
- * @param npages Number of PAGE_SIZE-sized pages in the region
- * @return True iff the region can be used with the current compression
- */
-bool pdx_is_region_compressible(paddr_t base, unsigned long npages);
-
 /**
  * Calculates a mask covering "moving" bits of all addresses of a region
  *
@@ -216,7 +207,9 @@ static inline paddr_t directmapoff_to_maddr(unsigned long 
offset)
  */
 void pfn_pdx_hole_setup(unsigned long mask);
 
-#else /* !CONFIG_PDX_COMPRESSION */
+#endif /* CONFIG_PDX_MASK_COMPRESSION */
+
+#ifdef CONFIG_PDX_NONE
 
 /* Without PDX compression we can skip some computations */
 
@@ -248,7 +241,20 @@ static inline void pfn_pdx_hole_setup(unsigned long mask)
 {
 }
 
-#endif /* CONFIG_PDX_COMPRESSION */
+#else /* !CONFIG_PDX_NONE */
+
+/* Shared functions implemented by all PDX compressions. */
+
+/**
+ * Validate a region's compatibility with the current compression runtime
+ *
+ * @param base Base address of the region
+ * @param npages Number of PAGE_SIZE-sized pages in the region
+ * @return True iff the region can be used with the current compression
+ */
+bool pdx_is_region_compressible(paddr_t base, unsigned long npages);
+
+#endif /* !CONFIG_PDX_NONE */
 #endif /* __XEN_PDX_H__ */
 
 /*
-- 
2.49.0