EDAC/altera: Add SDRAM ECC check for U-Boot

A bug in legacy U-Boot causes a crash during SDRAM boot if ECC is not
enabled in the bitstream but enabled in the Linux config.

Memory mapped read of the ECC Enabled bit was only enabled if U-Boot
determined ECC was enabled in the bitstream.

The Linux driver checks the ECC enable bit using a memory map read.
In the ECC disabled bitstream case, U-Boot didn't enable ECC register
memory map reads and since they are not allowed this results in a crash.

Always read the ECC Enable register through a SMC call which is always
allowed and it works with legacy and current U-Boot.

  [ bp: Massage commit message. ]

Signed-off-by: Rabara Niravkumar L <niravkumar.l.rabara@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dinh Nguyen <dinguyen@kernel.org>
Link: https://lore.kernel.org/r/20220305014118.4794-1-niravkumar.l.rabara@intel.com

drivers/edac/altera_edac.c

@@ -1083,8 +1083,46 @@ static int __init __maybe_unused altr_init_a10_ecc_device_type(char *compat)
 
 #ifdef CONFIG_EDAC_ALTERA_SDRAM
 
+/*
+ * A legacy U-Boot bug only enabled memory mapped access to the ECC Enable
+ * register if ECC is enabled. Linux checks the ECC Enable register to
+ * determine ECC status.
+ * Use an SMC call (which always works) to determine ECC enablement.
+ */
+static int altr_s10_sdram_check_ecc_deps(struct altr_edac_device_dev *device)
+{
+	const struct edac_device_prv_data *prv = device->data;
+	unsigned long sdram_ecc_addr;
+	struct arm_smccc_res result;
+	struct device_node *np;
+	phys_addr_t sdram_addr;
+	u32 read_reg;
+	int ret;
+
+	np = of_find_compatible_node(NULL, NULL, "altr,sdr-ctl");
+	if (!np)
+		goto sdram_err;
+
+	sdram_addr = of_translate_address(np, of_get_address(np, 0,
+							     NULL, NULL));
+	of_node_put(np);
+	sdram_ecc_addr = (unsigned long)sdram_addr + prv->ecc_en_ofst;
+	arm_smccc_smc(INTEL_SIP_SMC_REG_READ, sdram_ecc_addr,
+		      0, 0, 0, 0, 0, 0, &result);
+	read_reg = (unsigned int)result.a1;
+	ret = (int)result.a0;
+	if (!ret && (read_reg & prv->ecc_enable_mask))
+		return 0;
+
+sdram_err:
+	edac_printk(KERN_ERR, EDAC_DEVICE,
+		    "%s: No ECC present or ECC disabled.\n",
+		    device->edac_dev_name);
+	return -ENODEV;
+}
+
 static const struct edac_device_prv_data s10_sdramecc_data = {
-	.setup = altr_check_ecc_deps,
+	.setup = altr_s10_sdram_check_ecc_deps,
 	.ce_clear_mask = ALTR_S10_ECC_SERRPENA,
 	.ue_clear_mask = ALTR_S10_ECC_DERRPENA,
 	.ecc_enable_mask = ALTR_S10_ECC_EN,