[PATCH v3 8/9] serial: msm-geni: correct oversampling value based on QUP hardware revision

[Vladimir Zapolskiy]

Starting from QUP v2.5 the value of oversampling is changed from 32
to 16, keeping the old value on newer platforms results on wrong set
UART IP clock divider, thus the asked baudrate does not correspond to
the actually set with all the consequencies for a user.

The change links the driver to a new Qualcomm GENI SE QUP driver
to get its hardware version and update the oversampling value.

Deliberately the code under CONFIG_DEBUG_UART_MSM_GENI is not touched,
since a wanted baudrate can be controlled by setting a modified
CONFIG_DEBUG_UART_CLOCK build time variable.

Signed-off-by: Vladimir Zapolskiy <vladimir.zapolskiy at linaro.org>
---
 drivers/serial/Kconfig           |  2 ++
 drivers/serial/serial_msm_geni.c | 35 +++++++++++++++++++++++++++++++-
 2 files changed, 36 insertions(+), 1 deletion(-)

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index bb5083201b38..d50a1fd3f382 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -938,6 +938,8 @@ config MSM_SERIAL
 
 config MSM_GENI_SERIAL
 	bool "Qualcomm on-chip GENI UART"
+	select MISC
+	imply QCOM_GENI_SE
 	help
 	  Support UART based on Generic Interface (GENI) Serial Engine (SE),
 	  used on Qualcomm Snapdragon SoCs. Should support all qualcomm SOCs
diff --git a/drivers/serial/serial_msm_geni.c b/drivers/serial/serial_msm_geni.c
index 29fae810d6fe..78fd9389c036 100644
--- a/drivers/serial/serial_msm_geni.c
+++ b/drivers/serial/serial_msm_geni.c
@@ -13,6 +13,7 @@
 #include <dm.h>
 #include <errno.h>
 #include <linux/delay.h>
+#include <misc.h>
 #include <serial.h>
 
 #define UART_OVERSAMPLING	32
@@ -110,6 +111,10 @@
 #define TX_FIFO_DEPTH_MSK	(GENMASK(21, 16))
 #define TX_FIFO_DEPTH_SHFT	16
 
+/* GENI SE QUP Registers */
+#define QUP_HW_VER_REG		0x4
+#define  QUP_SE_VERSION_2_5	0x20050000
+
 /*
  * Predefined packing configuration of the serial engine (CFG0, CFG1 regs)
  * for uart mode.
@@ -127,6 +132,7 @@ DECLARE_GLOBAL_DATA_PTR;
 struct msm_serial_data {
 	phys_addr_t base;
 	u32 baud;
+	u32 oversampling;
 };
 
 unsigned long root_freq[] = {7372800,  14745600, 19200000, 29491200,
@@ -246,7 +252,7 @@ static int msm_serial_setbrg(struct udevice *dev, int baud)
 
 	priv->baud = baud;
 
-	clk_rate = get_clk_div_rate(baud, UART_OVERSAMPLING, &clk_div);
+	clk_rate = get_clk_div_rate(baud, priv->oversampling, &clk_div);
 	geni_serial_set_clock_rate(dev, clk_rate);
 	geni_serial_baud(priv->base, clk_div, baud);
 
@@ -480,6 +486,31 @@ static const struct dm_serial_ops msm_serial_ops = {
 	.setbrg = msm_serial_setbrg,
 };
 
+static void geni_set_oversampling(struct udevice *dev)
+{
+	struct msm_serial_data *priv = dev_get_priv(dev);
+	struct udevice *parent_dev = dev_get_parent(dev);
+	u32 geni_se_version;
+	int ret;
+
+	priv->oversampling = UART_OVERSAMPLING;
+
+	/*
+	 * It could happen that GENI SE IP is missing in the board's device
+	 * tree or GENI UART node is a direct child of SoC device tree node.
+	 */
+	if (device_get_uclass_id(parent_dev) != UCLASS_MISC)
+		return;
+
+	ret = misc_read(parent_dev, QUP_HW_VER_REG,
+			&geni_se_version, sizeof(geni_se_version));
+	if (ret != sizeof(geni_se_version))
+		return;
+
+	if (geni_se_version >= QUP_SE_VERSION_2_5)
+		priv->oversampling /= 2;
+}
+
 static inline void geni_serial_init(struct udevice *dev)
 {
 	struct msm_serial_data *priv = dev_get_priv(dev);
@@ -523,6 +554,8 @@ static int msm_serial_probe(struct udevice *dev)
 {
 	struct msm_serial_data *priv = dev_get_priv(dev);
 
+	geni_set_oversampling(dev);
+
 	/* No need to reinitialize the UART after relocation */
 	if (gd->flags & GD_FLG_RELOC)
 		return 0;
-- 
2.33.0