[PATCH] FPGA2SDRAM setup fix

[Brian Sune]

After testing, w/o proper setup
the FPGA2SDRAM bridge will not work and stall.
Pulling from official fix and w/o this initialization,
both 2025.07 and 2025.10 also suffer stall on U-Boot
and distro. Any FPGA to HPS-SDRAM action will immediate
stall the CPU. As such, this patch fix the issue.

Signed-off-by: Brian Sune <briansune at gmail.com>
---
 arch/arm/mach-socfpga/misc_gen5.c | 34 ++++++++++++++++++++++++++++++-
 1 file changed, 33 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-socfpga/misc_gen5.c b/arch/arm/mach-socfpga/misc_gen5.c
index b136691c685..5259ef54d73 100644
--- a/arch/arm/mach-socfpga/misc_gen5.c
+++ b/arch/arm/mach-socfpga/misc_gen5.c
@@ -217,6 +217,34 @@ int arch_early_init_r(void)
 static struct socfpga_sdr_ctrl *sdr_ctrl =
 	(struct socfpga_sdr_ctrl *)SDR_CTRLGRP_ADDRESS;
 
+void socfpga_sdram_apply_static_cfg(void)
+{
+	const u32 applymask = 0x8;
+	u32 val = readl(&sdr_ctrl->static_cfg) | applymask;
+
+	/*
+	 * SDRAM staticcfg register specific:
+	 * When applying the register setting, the CPU must not access
+	 * SDRAM. Luckily for us, we can use i-cache here to help us
+	 * circumvent the SDRAM access issue. The idea is to make sure
+	 * that the code is in one full i-cache line by branching past
+	 * it and back. Once it is in the i-cache, we execute the core
+	 * of the code and apply the register settings.
+	 *
+	 * The code below uses 7 instructions, while the Cortex-A9 has
+	 * 32-byte cachelines, thus the limit is 8 instructions total.
+	 */
+	asm volatile(".align	5			\n"
+		     "		b 2f			\n"
+		     "1: 	str %0,	[%1]		\n"
+		     "		dsb			\n"
+		     "		isb			\n"
+		     "		b 3f			\n"
+		     "2:	b 1b			\n"
+		     "3:	nop			\n"
+		    : : "r"(val), "r"(&sdr_ctrl->static_cfg) : "memory", "cc");
+}
+
 void do_bridge_reset(int enable, unsigned int mask)
 {
 	int i;
@@ -234,7 +262,10 @@ void do_bridge_reset(int enable, unsigned int mask)
 		writel(iswgrp_handoff[2],
 		       socfpga_get_sysmgr_addr() +
 		       SYSMGR_GEN5_FPGAINFGRP_MODULE);
-		writel(iswgrp_handoff[3], &sdr_ctrl->fpgaport_rst);
+		if (iswgrp_handoff[3]) {
+			writel(iswgrp_handoff[3], &sdr_ctrl->fpgaport_rst);
+			socfpga_sdram_apply_static_cfg();
+		}
 		writel(iswgrp_handoff[0],
 		       socfpga_get_rstmgr_addr() + RSTMGR_GEN5_BRGMODRST);
 		writel(iswgrp_handoff[1], &nic301_regs->remap);
@@ -246,6 +277,7 @@ void do_bridge_reset(int enable, unsigned int mask)
 		writel(0, socfpga_get_sysmgr_addr() +
 		       SYSMGR_GEN5_FPGAINFGRP_MODULE);
 		writel(0, &sdr_ctrl->fpgaport_rst);
+		socfpga_sdram_apply_static_cfg();
 		writel(0x7, socfpga_get_rstmgr_addr() + RSTMGR_GEN5_BRGMODRST);
 		writel(1, &nic301_regs->remap);
 	}
-- 
2.25.1