microblaze: Allow PAGE_SIZE configuration

Allow developer to configure memory page size at compile time.
Larger pages can improve performance on some workloads.

Based on PowerPC code.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>

6 files changed, 50 insertions, 11 deletions

diff --git a/arch/microblaze/Kconfig b/arch/microblaze/Kconfig
index 505a08592423..a51742190c12 100644
--- a/arch/microblaze/Kconfig
+++ b/arch/microblaze/Kconfig
@@ -223,6 +223,36 @@ config TASK_SIZE
         hex "Size of user task space" if TASK_SIZE_BOOL
         default "0x80000000"
 
+choice
+        prompt "Page size"
+        default MICROBLAZE_4K_PAGES
+        depends on ADVANCED_OPTIONS && !MMU
+        help
+          Select the kernel logical page size. Increasing the page size
+          will reduce software overhead at each page boundary, allow
+          hardware prefetch mechanisms to be more effective, and allow
+          larger dma transfers increasing IO efficiency and reducing
+          overhead. However the utilization of memory will increase.
+          For example, each cached file will using a multiple of the
+          page size to hold its contents and the difference between the
+          end of file and the end of page is wasted.
+
+          If unsure, choose 4K_PAGES.
+
+config MICROBLAZE_4K_PAGES
+        bool "4k page size"
+
+config MICROBLAZE_8K_PAGES
+        bool "8k page size"
+
+config MICROBLAZE_16K_PAGES
+        bool "16k page size"
+
+config MICROBLAZE_32K_PAGES
+        bool "32k page size"
+
+endchoice
+
 endmenu
 
 source "mm/Kconfig"
diff --git a/arch/microblaze/include/asm/elf.h b/arch/microblaze/include/asm/elf.h
index 7d4acf2b278e..732caf1be741 100644
--- a/arch/microblaze/include/asm/elf.h
+++ b/arch/microblaze/include/asm/elf.h
@@ -77,7 +77,7 @@ typedef elf_fpreg_t elf_fpregset_t[ELF_NFPREG];
 #define ELF_DATA        ELFDATA2MSB
 #endif
 
-#define ELF_EXEC_PAGESIZE       4096
+#define ELF_EXEC_PAGESIZE       PAGE_SIZE
 
 
 #define ELF_CORE_COPY_REGS(_dest, _regs)                        \
diff --git a/arch/microblaze/include/asm/page.h b/arch/microblaze/include/asm/page.h
index 464ff32bee3d..c12c6dfafd9f 100644
--- a/arch/microblaze/include/asm/page.h
+++ b/arch/microblaze/include/asm/page.h
@@ -23,8 +23,16 @@
 #ifdef __KERNEL__
 
 /* PAGE_SHIFT determines the page size */
-#define PAGE_SHIFT      (12)
-#define PAGE_SIZE       (_AC(1, UL) << PAGE_SHIFT)
+#if defined(CONFIG_MICROBLAZE_32K_PAGES)
+#define PAGE_SHIFT              15
+#elif defined(CONFIG_MICROBLAZE_16K_PAGES)
+#define PAGE_SHIFT              14
+#elif defined(CONFIG_MICROBLAZE_8K_PAGES)
+#define PAGE_SHIFT              13
+#else
+#define PAGE_SHIFT              12
+#endif
+#define PAGE_SIZE       (ASM_CONST(1) << PAGE_SHIFT)
 #define PAGE_MASK       (~(PAGE_SIZE-1))
 
 #define LOAD_OFFSET     ASM_CONST((CONFIG_KERNEL_START-CONFIG_KERNEL_BASE_ADDR))
diff --git a/arch/microblaze/kernel/cpu/mb.c b/arch/microblaze/kernel/cpu/mb.c
index 4216eb1eaa32..7086e3564281 100644
--- a/arch/microblaze/kernel/cpu/mb.c
+++ b/arch/microblaze/kernel/cpu/mb.c
@@ -126,6 +126,7 @@ static int show_cpuinfo(struct seq_file *m, void *v)
                         cpuinfo.pvr_user1,
                         cpuinfo.pvr_user2);
 
+        count += seq_printf(m, "Page size:\t%lu\n", PAGE_SIZE);
         return 0;
 }
 
diff --git a/arch/microblaze/kernel/head.S b/arch/microblaze/kernel/head.S
index 1bf739888260..42434008209e 100644
--- a/arch/microblaze/kernel/head.S
+++ b/arch/microblaze/kernel/head.S
@@ -43,10 +43,10 @@
 .global empty_zero_page
 .align 12
 empty_zero_page:
-        .space  4096
+        .space  PAGE_SIZE
 .global swapper_pg_dir
 swapper_pg_dir:
-        .space  4096
+        .space  PAGE_SIZE
 
 #endif /* CONFIG_MMU */
 
diff --git a/arch/microblaze/kernel/vmlinux.lds.S b/arch/microblaze/kernel/vmlinux.lds.S
index db72d7124602..b0de1a6b5513 100644
--- a/arch/microblaze/kernel/vmlinux.lds.S
+++ b/arch/microblaze/kernel/vmlinux.lds.S
@@ -55,7 +55,7 @@ SECTIONS {
          */
         .sdata2 : AT(ADDR(.sdata2) - LOAD_OFFSET) {
                 _ssrw = .;
-                . = ALIGN(4096); /* page aligned when MMU used - origin 0x8 */
+                . = ALIGN(PAGE_SIZE); /* page aligned when MMU used */
                 *(.sdata2)
         . = ALIGN(8);
         _essrw = .;
@@ -70,7 +70,7 @@ SECTIONS {
         /* Reserve some low RAM for r0 based memory references */
         . = ALIGN(0x4) ;
         r0_ram = . ;
-        . = . +  4096;  /* a page should be enough */
+        . = . +  PAGE_SIZE;     /* a page should be enough */
 
         /* Under the microblaze ABI, .sdata and .sbss must be contiguous */
         . = ALIGN(8);
@@ -120,7 +120,7 @@ SECTIONS {
 
         __init_end_before_initramfs = .;
 
-        .init.ramfs ALIGN(4096) : AT(ADDR(.init.ramfs) - LOAD_OFFSET) {
+        .init.ramfs ALIGN(PAGE_SIZE) : AT(ADDR(.init.ramfs) - LOAD_OFFSET) {
                 __initramfs_start = .;
                 *(.init.ramfs)
                 __initramfs_end = .;
@@ -132,11 +132,11 @@ SECTIONS {
  * so that __init_end == __bss_start. This will make image.elf
  * consistent with the image.bin
  */
-                /* . = ALIGN(4096); */
+                /* . = ALIGN(PAGE_SIZE); */
         }
         __init_end = .;
 
-        .bss ALIGN (4096) : AT(ADDR(.bss) - LOAD_OFFSET) {
+        .bss ALIGN (PAGE_SIZE) : AT(ADDR(.bss) - LOAD_OFFSET) {
                 /* page aligned when MMU used */
                 __bss_start = . ;
                         *(.bss*)
@@ -145,7 +145,7 @@ SECTIONS {
                 __bss_stop = . ;
                 _ebss = . ;
         }
-        . = ALIGN(4096);
+        . = ALIGN(PAGE_SIZE);
         _end = .;
 
         DISCARDS