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Subject[PATCH v5 13/15] MIPS: JZ4770: Workaround for corrupted DMA transfers
Date
From: Maarten ter Huurne <maarten@treewalker.org>

We have seen MMC DMA transfers read corrupted data from SDRAM when
a burst interval ends at physical address 0x10000000. To avoid this
problem, we remove the final page of low memory from the memory map.

Signed-off-by: Maarten ter Huurne <maarten@treewalker.org>
---
arch/mips/jz4740/setup.c | 24 ++++++++++++++++++++++++
arch/mips/kernel/setup.c | 8 ++++++++
2 files changed, 32 insertions(+)

v2: No change
v3: No change
v4: No change
v5: No change

diff --git a/arch/mips/jz4740/setup.c b/arch/mips/jz4740/setup.c
index afd84ee966e8..6948b133a15d 100644
--- a/arch/mips/jz4740/setup.c
+++ b/arch/mips/jz4740/setup.c
@@ -23,6 +23,7 @@

#include <asm/bootinfo.h>
#include <asm/mips_machine.h>
+#include <asm/page.h>
#include <asm/prom.h>

#include <asm/mach-jz4740/base.h>
@@ -102,6 +103,29 @@ void __init arch_init_irq(void)
irqchip_init();
}

+/*
+ * We have seen MMC DMA transfers read corrupted data from SDRAM when a burst
+ * interval ends at physical address 0x10000000. To avoid this problem, we
+ * remove the final page of low memory from the memory map.
+ */
+void __init jz4770_reserve_unsafe_for_dma(void)
+{
+ int i;
+
+ for (i = 0; i < boot_mem_map.nr_map; i++) {
+ struct boot_mem_map_entry *entry = boot_mem_map.map + i;
+
+ if (entry->type != BOOT_MEM_RAM)
+ continue;
+
+ if (entry->addr + entry->size != 0x10000000)
+ continue;
+
+ entry->size -= PAGE_SIZE;
+ break;
+ }
+}
+
static int __init jz4740_machine_setup(void)
{
mips_machine_setup();
diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
index 85bc601e9a0d..5a2c20145aee 100644
--- a/arch/mips/kernel/setup.c
+++ b/arch/mips/kernel/setup.c
@@ -879,6 +879,14 @@ static void __init arch_mem_init(char **cmdline_p)

parse_early_param();

+#ifdef CONFIG_MACH_JZ4770
+ if (current_cpu_type() == CPU_JZRISC &&
+ mips_machtype == MACH_INGENIC_JZ4770) {
+ extern void __init jz4770_reserve_unsafe_for_dma(void);
+ jz4770_reserve_unsafe_for_dma();
+ }
+#endif
+
if (usermem) {
pr_info("User-defined physical RAM map:\n");
print_memory_map();
--
2.11.0
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