m68k/atari - stram: alloc ST-RAM pool even if kernel not in ST-RAM

With the kernel loaded to FastRAM (TT-RAM), none of the ST-RAM
address range is mapped by init_mem, and ST-RAM is not accessible
through the normal allocation pathways as a result.

Implement ST-RAM pool allocation to be based on physical addresses
always (it already was when the kernel was loaded in ST-RAM).
Return kernel virtual addresses as per normal.

The current test for the kernel residing in ST-RAM always returns
true. Use the bootinfo memory chunk order instead - with the kernel
in FastRAM, ST-RAM (phys. 0x0) is not the first chunk.

In case the kernel is running from FastRAM, delay mapping of ST-RAM
pool until after mem_init.

Provide helper functions for those users of ST-RAM that need
to be aware of the backing physical addresses.

Kudos to Geert for his hints on getting this started.

Signed-off-by: Michael Schmitz <schmitz@debian.org>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>

arch/m68k/atari/stram.c

@@ -47,6 +47,7 @@ static struct resource stram_pool = {
 
 static unsigned long pool_size = 1024*1024;
 
+static unsigned long stram_virt_offset;
 
 static int __init atari_stram_setup(char *arg)
 {
@@ -67,14 +68,12 @@ early_param("stram_pool", atari_stram_setup);
 void __init atari_stram_init(void)
 {
 	int i;
-	void *stram_start;
 
 	/*
 	 * determine whether kernel code resides in ST-RAM
 	 * (then ST-RAM is the first memory block at virtual 0x0)
 	 */
-	stram_start = phys_to_virt(0);
-	kernel_in_stram = (stram_start == 0);
+	kernel_in_stram = (m68k_memory[0].addr == 0);
 
 	for (i = 0; i < m68k_num_memory; ++i) {
 		if (m68k_memory[i].addr == 0) {
@@ -89,24 +88,62 @@ void __init atari_stram_init(void)
 
 /*
  * This function is called from setup_arch() to reserve the pages needed for
- * ST-RAM management.
+ * ST-RAM management, if the kernel resides in ST-RAM.
  */
 void __init atari_stram_reserve_pages(void *start_mem)
 {
-	/*
-	 * always reserve first page of ST-RAM, the first 2 KiB are
-	 * supervisor-only!
-	 */
-	if (!kernel_in_stram)
-		reserve_bootmem(0, PAGE_SIZE, BOOTMEM_DEFAULT);
+	if (kernel_in_stram) {
+		pr_debug("atari_stram pool: kernel in ST-RAM, using alloc_bootmem!\n");
+		stram_pool.start = (resource_size_t)alloc_bootmem_low_pages(pool_size);
+		stram_pool.end = stram_pool.start + pool_size - 1;
+		request_resource(&iomem_resource, &stram_pool);
+		stram_virt_offset = 0;
+		pr_debug("atari_stram pool: size = %lu bytes, resource = %pR\n",
+			pool_size, &stram_pool);
+		pr_debug("atari_stram pool: stram_virt_offset = %lx\n",
+			stram_virt_offset);
+	}
+}
 
-	stram_pool.start = (resource_size_t)alloc_bootmem_low_pages(pool_size);
-	stram_pool.end = stram_pool.start + pool_size - 1;
-	request_resource(&iomem_resource, &stram_pool);
 
-	pr_debug("atari_stram pool: size = %lu bytes, resource = %pR\n",
-		 pool_size, &stram_pool);
+/*
+ * This function is called as arch initcall to reserve the pages needed for
+ * ST-RAM management, if the kernel does not reside in ST-RAM.
+ */
+int __init atari_stram_map_pages(void)
+{
+	if (!kernel_in_stram) {
+		/*
+		 * Skip page 0, as the fhe first 2 KiB are supervisor-only!
+		 */
+		pr_debug("atari_stram pool: kernel not in ST-RAM, using ioremap!\n");
+		stram_pool.start = PAGE_SIZE;
+		stram_pool.end = stram_pool.start + pool_size - 1;
+		request_resource(&iomem_resource, &stram_pool);
+		stram_virt_offset = (unsigned long) ioremap(stram_pool.start,
+				resource_size(&stram_pool)) - stram_pool.start;
+		pr_debug("atari_stram pool: size = %lu bytes, resource = %pR\n",
+			pool_size, &stram_pool);
+		pr_debug("atari_stram pool: stram_virt_offset = %lx\n",
+			stram_virt_offset);
+	}
+	return 0;
+}
+arch_initcall(atari_stram_map_pages);
+
+
+void *atari_stram_to_virt(unsigned long phys)
+{
+	return (void *)(phys + stram_virt_offset);
+}
+EXPORT_SYMBOL(atari_stram_to_virt);
+
+
+unsigned long atari_stram_to_phys(void *virt)
+{
+	return (unsigned long)(virt - stram_virt_offset);
 }
+EXPORT_SYMBOL(atari_stram_to_phys);
 
 
 void *atari_stram_alloc(unsigned long size, const char *owner)
@@ -134,14 +171,14 @@ void *atari_stram_alloc(unsigned long size, const char *owner)
 	}
 
 	pr_debug("atari_stram_alloc: returning %pR\n", res);
-	return (void *)res->start;
+	return atari_stram_to_virt(res->start);
 }
 EXPORT_SYMBOL(atari_stram_alloc);
 
 
 void atari_stram_free(void *addr)
 {
-	unsigned long start = (unsigned long)addr;
+	unsigned long start = atari_stram_to_phys(addr);
 	struct resource *res;
 	unsigned long size;
 

arch/m68k/include/asm/atari_stram.h

@@ -8,6 +8,8 @@
 /* public interface */
 void *atari_stram_alloc(unsigned long size, const char *owner);
 void atari_stram_free(void *);
+void *atari_stram_to_virt(unsigned long phys);
+unsigned long atari_stram_to_phys(void *);
 
 /* functions called internally by other parts of the kernel */
 void atari_stram_init(void);