[RFC] serial: pl01x: add sbsa-uart favor

[AKASHI Takahiro]

sbsa-uart is a virtual UART device with a sub-set of PL011 functionality
which is described in SBSA (Server Base System Architecture)[1].

It mainly targets for server use, but sbsa-uart itself is useful in any
para-virtualized use cases, including Xen.

At present, this patch is submitted as RFC because:
* for some reason, data cache must be turned off (in initr_dcache())
* there is a prerequisite patch for Xen[2]

The patch with xenguest_arm64_defconfig was tested on upstream Xen and
qemu-arm64.
(To work with xenguest_arm64_defconfig, minor and non-essential tweaks
are needed.)

The output looks like:
U-Boot 2021.01-rc1-00005-g3b8e3cde5345 (Nov 04 2020 - 13:54:44 +0900) xenguest

Xen virtual CPU
Model: XENVM-4.15
DRAM:  128 MiB
PVBLOCK: Failed to read device/vbd directory: ENOENT

In:    sbsa-pl011
Out:   sbsa-pl011
Err:   sbsa-pl011
xenguest# dm tree
 Class     Index  Probed  Driver                Name
-----------------------------------------------------------
 root          0  [ + ]   root_driver           root_driver
 firmware      0  [   ]   psci                  |-- psci
 serial        0  [ + ]   serial_pl01x          |-- sbsa-pl011
 pvblock       0  [   ]   pvblock               `-- pvblock

[1] https://developer.arm.com/architectures/platform-design/server-systems
[2] https://lists.xenproject.org/archives/html/xen-devel/2020-10/msg02122.html

Signed-off-by: AKASHI Takahiro <takahiro.akashi at linaro.org>
---
 drivers/serial/Kconfig                  | 13 +++++++++++--
 drivers/serial/serial_pl01x.c           | 16 +++++++++++++---
 include/dm/platform_data/serial_pl01x.h |  1 +
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index b4805a2e4ea4..fb570174c577 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -332,6 +332,15 @@ config DEBUG_UART_PL011
 	  work. The driver will be available until the real driver model
 	  serial is running.
 
+config DEBUG_UART_SBSA
+	bool "sbsa-uart"
+	depends on PL01X_SERIAL
+	help
+	  Select this to enable a debug UART using the pl01x driver with the
+	  SBSA_UART type. You will need to provide parameters to make this
+	  work. The driver will be available until the real driver model
+	  serial is running.
+
 config DEBUG_UART_PIC32
 	bool "Microchip PIC32"
 	depends on PIC32_SERIAL
@@ -415,7 +424,7 @@ config DEBUG_UART_BASE
 
 config DEBUG_UART_CLOCK
 	int "UART input clock"
-	depends on DEBUG_UART
+	depends on DEBUG_UART && !DEBUG_UART_SBSA
 	default 0 if DEBUG_UART_SANDBOX
 	help
 	  The UART input clock determines the speed of the internal UART
@@ -427,7 +436,7 @@ config DEBUG_UART_CLOCK
 
 config DEBUG_UART_SHIFT
 	int "UART register shift"
-	depends on DEBUG_UART
+	depends on DEBUG_UART && !DEBUG_UART_SBSA
 	default 0 if DEBUG_UART
 	help
 	  Some UARTs (notably ns16550) support different register layouts
diff --git a/drivers/serial/serial_pl01x.c b/drivers/serial/serial_pl01x.c
index 2772c25f1d2d..5ef4ae0c6a65 100644
--- a/drivers/serial/serial_pl01x.c
+++ b/drivers/serial/serial_pl01x.c
@@ -84,6 +84,8 @@ static int pl01x_generic_serial_init(struct pl01x_regs *regs,
 		/* disable everything */
 		writel(0, &regs->pl011_cr);
 		break;
+	case TYPE_SBSA_UART:
+		break;
 	default:
 		return -EINVAL;
 	}
@@ -146,7 +148,8 @@ static int pl01x_generic_setbrg(struct pl01x_regs *regs, enum pl01x_type type,
 		writel(UART_PL010_CR_UARTEN, &regs->pl010_cr);
 		break;
 	}
-	case TYPE_PL011: {
+	case TYPE_PL011:
+	case TYPE_SBSA_UART: {
 		unsigned int temp;
 		unsigned int divider;
 		unsigned int remainder;
@@ -171,6 +174,9 @@ static int pl01x_generic_setbrg(struct pl01x_regs *regs, enum pl01x_type type,
 			writel(fraction, &regs->pl011_fbrd);
 		}
 
+		if (type == TYPE_SBSA_UART)
+			break;
+
 		pl011_set_line_control(regs);
 		/* Finally, enable the UART */
 		writel(UART_PL011_CR_UARTEN | UART_PL011_CR_TXE |
@@ -340,6 +346,7 @@ static const struct dm_serial_ops pl01x_serial_ops = {
 static const struct udevice_id pl01x_serial_id[] ={
 	{.compatible = "arm,pl011", .data = TYPE_PL011},
 	{.compatible = "arm,pl010", .data = TYPE_PL010},
+	{.compatible = "arm,sbsa-uart", .data = TYPE_SBSA_UART},
 	{}
 };
 
@@ -386,7 +393,8 @@ U_BOOT_DRIVER(serial_pl01x) = {
 
 #endif
 
-#if defined(CONFIG_DEBUG_UART_PL010) || defined(CONFIG_DEBUG_UART_PL011)
+#if defined(CONFIG_DEBUG_UART_PL010) || defined(CONFIG_DEBUG_UART_PL011) || \
+    defined(CONFIG_DEBUG_UART_SBSA)
 
 #include <debug_uart.h>
 
@@ -395,7 +403,9 @@ static void _debug_uart_init(void)
 #ifndef CONFIG_DEBUG_UART_SKIP_INIT
 	struct pl01x_regs *regs = (struct pl01x_regs *)CONFIG_DEBUG_UART_BASE;
 	enum pl01x_type type = CONFIG_IS_ENABLED(DEBUG_UART_PL011) ?
-				TYPE_PL011 : TYPE_PL010;
+				TYPE_PL011 :
+			       (CONFIG_IS_ENABLED(DEBUG_UART_PL010) ?
+				TYPE_PL010 : TYPE_SBSA_UART);
 
 	pl01x_generic_serial_init(regs, type);
 	pl01x_generic_setbrg(regs, type,
diff --git a/include/dm/platform_data/serial_pl01x.h b/include/dm/platform_data/serial_pl01x.h
index 77d96c49f03a..4bacbd512400 100644
--- a/include/dm/platform_data/serial_pl01x.h
+++ b/include/dm/platform_data/serial_pl01x.h
@@ -9,6 +9,7 @@
 enum pl01x_type {
 	TYPE_PL010,
 	TYPE_PL011,
+	TYPE_SBSA_UART,
 };
 
 /*
-- 
2.28.0