[PATCH] ARM: cpu: start: don't panic when only initial memory known

[Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>]

Boards that get their memory from device tree are prone to breakage if
upstream decides to remove the /memory node or renders it unusable[0]
or to disable the DRAM controller device node[1] used to dynamically
compute the size.  While this needs to be fixed properly on a
case-by-case basis, soften the blow by using the memory size specified
by low level code as a fallback instead of just throwing the towel.

[0]: aa68c6bd3615 ("arm: rk3288-phycore-som: Fix memory node")
[1]: 0529149b2756 ("arm: imx8mq: re-enable DDRC for Barebox")
Signed-off-by: Ahmad Fatoum <a.fatoum@xxxxxxxxxxxxxx>
---
 arch/arm/cpu/mmu-common.c          | 15 +++++++++++++--
 arch/arm/cpu/start.c               |  8 ++++++++
 arch/arm/include/asm/barebox-arm.h |  1 +
 3 files changed, 22 insertions(+), 2 deletions(-)

diff --git a/arch/arm/cpu/mmu-common.c b/arch/arm/cpu/mmu-common.c
index 2ef1fa231f39..488a189f1c06 100644
--- a/arch/arm/cpu/mmu-common.c
+++ b/arch/arm/cpu/mmu-common.c
@@ -9,6 +9,7 @@
 #include <dma.h>
 #include <mmu.h>
 #include <asm/system.h>
+#include <asm/barebox-arm.h>
 #include <memory.h>
 #include "mmu.h"
 
@@ -58,14 +59,24 @@ void dma_free_coherent(void *mem, dma_addr_t dma_handle, size_t size)
 
 static int mmu_init(void)
 {
-	if (list_empty(&memory_banks))
+	if (list_empty(&memory_banks)) {
+		resource_size_t start;
+		int ret;
+
 		/*
 		 * If you see this it means you have no memory registered.
 		 * This can be done either with arm_add_mem_device() in an
 		 * initcall prior to mmu_initcall or via devicetree in the
 		 * memory node.
 		 */
-		panic("MMU: No memory bank found! Cannot continue\n");
+		pr_emerg("No memory bank registered. Limping along with initial memory\n");
+
+		start = arm_mem_membase_get();
+		ret = barebox_add_memory_bank("initmem", start,
+					      arm_mem_endmem_get() - start);
+		if (ret)
+			panic("");
+	}
 
 	__mmu_init(get_cr() & CR_M);
 
diff --git a/arch/arm/cpu/start.c b/arch/arm/cpu/start.c
index c61db668658b..14cc310312ab 100644
--- a/arch/arm/cpu/start.c
+++ b/arch/arm/cpu/start.c
@@ -28,6 +28,7 @@
 unsigned long arm_stack_top;
 static unsigned long arm_barebox_size;
 static unsigned long arm_endmem;
+static unsigned long arm_membase;
 static void *barebox_boarddata;
 static unsigned long barebox_boarddata_size;
 
@@ -114,6 +115,12 @@ unsigned long arm_mem_endmem_get(void)
 }
 EXPORT_SYMBOL_GPL(arm_mem_endmem_get);
 
+unsigned long arm_mem_membase_get(void)
+{
+	return arm_membase;
+}
+EXPORT_SYMBOL_GPL(arm_mem_membase_get);
+
 static int barebox_memory_areas_init(void)
 {
 	if(barebox_boarddata)
@@ -148,6 +155,7 @@ __noreturn __no_sanitize_address void barebox_non_pbl_start(unsigned long membas
 
 	pr_debug("memory at 0x%08lx, size 0x%08lx\n", membase, memsize);
 
+	arm_membase = membase;
 	arm_endmem = endmem;
 	arm_stack_top = arm_mem_stack_top(membase, endmem);
 	arm_barebox_size = barebox_size;
diff --git a/arch/arm/include/asm/barebox-arm.h b/arch/arm/include/asm/barebox-arm.h
index 15b3b6c44479..8240cce9bf5b 100644
--- a/arch/arm/include/asm/barebox-arm.h
+++ b/arch/arm/include/asm/barebox-arm.h
@@ -84,6 +84,7 @@ static inline void boarddata_create(void *adr, u32 machine)
 u32 barebox_arm_machine(void);
 
 unsigned long arm_mem_ramoops_get(void);
+unsigned long arm_mem_membase_get(void);
 unsigned long arm_mem_endmem_get(void);
 
 struct barebox_arm_boarddata *barebox_arm_get_boarddata(void);
-- 
2.30.2