[U-Boot] [PATCH v4 5/9] reset: socfpga: add reset handling for old kernels

[Simon Goldschmidt]

This adds code to take peripherals out of reset based on an environment
variable. This is in preparation for removing the code that does this from
SPL.

However, some drivers even in current Linux cannot handle peripheral reset,
so until this works, we need a compatibility workaround.

This workaround is implemented in the 'assert' and 'remove' callbacks of
this reset driver: the 'assert' callback does not disable peripherals that
were already taken out of reset, while the 'remove' callback, which is
called on OS_PREPARE, deasserts all peripheral resets if the environment
variable "socfpga_legacy_reset_compat" is set to 1, which is what the gen5
SPL did up to now.

This is in preparation to clean up the SPL and implementing proper reset
handling for U-Boot.

Signed-off-by: Simon Goldschmidt <simon.k.r.goldschmidt at gmail.com>
---

Changes in v4: None
Changes in v3:
- fix falcon mode in SPL should work, too
- change env var name "socfpga_permodrst_ungate" to
  "socfpga_legacy_reset_compat"
- in compat mode, don't reset peripherals once they are enabled

Changes in v2:
- moved from Kernel option "OLD_SOCFPGA_KERNEL_COMPAT" to environment
  variable "socfpga_permodrst_ungate"

 drivers/reset/reset-socfpga.c | 44 +++++++++++++++++++++++++++++++++++
 1 file changed, 44 insertions(+)

diff --git a/drivers/reset/reset-socfpga.c b/drivers/reset/reset-socfpga.c
index 244db51d85..cb8312619f 100644
--- a/drivers/reset/reset-socfpga.c
+++ b/drivers/reset/reset-socfpga.c
@@ -27,6 +27,36 @@ struct socfpga_reset_data {
 	void __iomem *modrst_base;
 };
 
+/*
+ * For compatibility with Kernels that don't support peripheral reset, this
+ * driver can keep the old behaviour of not asserting peripheral reset before
+ * starting the OS and deasserting all peripheral resets (enabling all
+ * peripherals).
+ *
+ * For that, the reset driver checks the environment variable
+ * "socfpga_legacy_reset_compat". If this variable is '1', perihperals are not
+ * reset again once taken out of reset and all peripherals in 'permodrst' are
+ * taken out of reset before booting into the OS.
+ * Note that this should be required for gen5 systems only that are running
+ * Linux kernels without proper peripheral reset support for all drivers used.
+ */
+static bool socfpga_reset_keep_enabled(void)
+{
+#if !defined(CONFIG_SPL_BUILD) || CONFIG_IS_ENABLED(ENV_SUPPORT)
+	const char *env_str;
+	long val;
+
+	env_str = env_get("socfpga_legacy_reset_compat");
+	if (env_str) {
+		val = simple_strtol(env_str, NULL, 0);
+		if (val == 1)
+			return true;
+	}
+#endif
+
+	return false;
+}
+
 static int socfpga_reset_assert(struct reset_ctl *reset_ctl)
 {
 	struct socfpga_reset_data *data = dev_get_priv(reset_ctl->dev);
@@ -90,6 +120,18 @@ static int socfpga_reset_probe(struct udevice *dev)
 	return 0;
 }
 
+static int socfpga_reset_remove(struct udevice *dev)
+{
+	struct socfpga_reset_data *data = dev_get_priv(dev);
+
+	if (socfpga_reset_keep_enabled()) {
+		puts("Deasserting all peripheral resets\n");
+		writel(0, data->modrst_base + 4);
+	}
+
+	return 0;
+}
+
 static const struct udevice_id socfpga_reset_match[] = {
 	{ .compatible = "altr,rst-mgr" },
 	{ /* sentinel */ },
@@ -102,4 +144,6 @@ U_BOOT_DRIVER(socfpga_reset) = {
 	.probe = socfpga_reset_probe,
 	.priv_auto_alloc_size = sizeof(struct socfpga_reset_data),
 	.ops = &socfpga_reset_ops,
+	.remove = socfpga_reset_remove,
+	.flags	= DM_FLAG_OS_PREPARE,
 };
-- 
2.17.1