[PATCH] ARM: rockchip: dmc: fix DRAM for sizes 16+ GiB on rk3588

[Michael Tretter <m.tretter@pengutronix.de>]

RK3588 has two known memory gaps when using 16+ GiB DRAM,
[0x3fc000000, 0x3fc500000) and [0x3fff00000, 0x400000000).

Skip both gaps when initializing the DRAM on rk3588 to avoid running
into an exception when running memtest on an rk3588 board with 16+ GiB
DRAM.

The information about the gaps is taken from a patch by Jonas Karlman to
the U-Boot mailing list [0].

[0] https://lore.kernel.org/all/20250405153832.1427549-5-jonas@kwiboo.se/

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
---
The start and end addresses of the gaps probably should be put into of
rockchip_dmc_drvdata and only set for the rk3588. Any suggestion how to
implement this more nicely would be very welcome.
---
 arch/arm/mach-rockchip/dmc.c | 20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/arch/arm/mach-rockchip/dmc.c b/arch/arm/mach-rockchip/dmc.c
index 86e61f311661..cf63fdb5a8bb 100644
--- a/arch/arm/mach-rockchip/dmc.c
+++ b/arch/arm/mach-rockchip/dmc.c
@@ -27,6 +27,12 @@
 #define RK3568_INT_REG_START		RK3399_INT_REG_START
 #define RK3588_INT_REG_START		RK3399_INT_REG_START
 
+/* RK3588 has two known memory gaps when using 16+ GiB DRAM */
+#define DRAM_GAP1_START         0x3fc000000
+#define DRAM_GAP1_END           0x3fc500000
+#define DRAM_GAP2_START         0x3fff00000
+#define DRAM_GAP2_END           0x400000000
+
 struct rockchip_dmc_drvdata {
 	unsigned int os_reg2;
 	unsigned int os_reg3;
@@ -220,9 +226,19 @@ static int rockchip_dmc_probe(struct device *dev)
 	arm_add_mem_device("ram0", membase,
 		min_t(resource_size_t, drvdata->internal_registers_start, memsize) - membase);
 
-	/* ram1, remaining RAM beyond 32bit space */
+	/* ram1, RAM beyond 32bit space up to first gap */
 	if (memsize > SZ_4G)
-		arm_add_mem_device("ram1", SZ_4G, memsize - SZ_4G);
+		arm_add_mem_device("ram1", SZ_4G,
+			min_t(resource_size_t, DRAM_GAP1_START, memsize) - SZ_4G);
+
+	/* ram2, RAM between first and second gap */
+	if (memsize > DRAM_GAP1_END)
+		arm_add_mem_device("ram2", DRAM_GAP1_END,
+			min_t(resource_size_t, DRAM_GAP2_START, memsize) - DRAM_GAP1_END);
+
+	/* ram3, remaining RAM after second gap */
+	if (memsize > DRAM_GAP2_END)
+		arm_add_mem_device("ram3", DRAM_GAP2_END, memsize - DRAM_GAP2_END);
 
 	return 0;
 }
-- 
2.39.5