From: Peter Delevoryas <p...@fb.com>
UART5 is typically used as the default debug UART on the AST2600, but
UART1 is also designed to be a debug UART. All the AST2600 UART's have
semi-configurable clock rates through registers in the System Control
Unit (SCU), but only UART5 works out of the box with zero-initialized
values. The rest of the UART's expect a few of the registers to be
initialized to non-zero values, or else the clock rate calculation will
yield zero or undefined (due to a divide-by-zero).
For reference, the U-Boot clock rate driver here shows the calculation:
https://github.com/facebook/openbmc-uboot/blob/main/drivers/clk/aspeed/clk_ast2600.c#L357)
To summarize, UART5 allows selection from 4 rates: 24 MHz, 192 MHz, 24 /
13 MHz, and 192 / 13 MHz. The other UART's allow selecting either the
"low" rate (UARTCLK) or the "high" rate (HUARTCLK). UARTCLK and HUARTCLK
are configurable themselves:
UARTCLK = UXCLK * R / (N * 2)
HUARTCLK = HUXCLK * HR / (HN * 2)
UXCLK and HUXCLK are also configurable, and depend on the APLL and/or
HPLL clock rates, which also derive from complicated calculations. Long
story short, there's lots of multiplication and division from
configurable registers, and most of these registers are zero-initialized
in QEMU, which at best is unexpected and at worst causes this clock rate
driver to hang from divide-by-zero's. This can also be difficult to
diagnose, because it may cause U-Boot to hang before serial console
initialization completes, requiring intervention from gdb.
This change just initializes all of these registers with default values
from the datasheet.
To test this, I used Facebook's AST2600 OpenBMC image for "fuji", with
the following diff applied (because fuji uses UART1 for console output,
not UART5).
diff --git a/hw/arm/aspeed_ast2600.c b/hw/arm/aspeed_ast2600.c
index e3013128c6..19da92979d 100644
--- a/hw/arm/aspeed_ast2600.c
+++ b/hw/arm/aspeed_ast2600.c
@@ -323,8 +323,8 @@ static void aspeed_soc_ast2600_realize(DeviceState *dev,
Error **errp)
}
/* UART - attach an 8250 to the IO space as our UART5 */
- serial_mm_init(get_system_memory(), sc->memmap[ASPEED_DEV_UART5], 2,
- aspeed_soc_get_irq(s, ASPEED_DEV_UART5),
+ serial_mm_init(get_system_memory(), sc->memmap[ASPEED_DEV_UART1], 2,
+ aspeed_soc_get_irq(s, ASPEED_DEV_UART1),
38400, serial_hd(0), DEVICE_LITTLE_ENDIAN);
/* I2C */
Without these clock rate registers being initialized, U-Boot hangs in
the clock rate driver from a divide-by-zero, because the UART1 clock
rate register reads return zero, and there's no console output. After
initializing them with default values, fuji boots successfully.
git clone https://github.com/facebook/openbmc
cd openbmc
./sync_yocto.sh
source openbmc-init-build-env fuji build-fuji
bitbake fuji-image
cp ./tmp/deploy/images/fuji/flash-fuji /tmp/
dd if=/dev/zero of=/tmp/fixedsize-fuji bs=1M count=128
dd if=/tmp/flash-fuji of=/tmp/fixedsize-fuji bs=1k conv=notrunc
git clone --branch init-clock-sel-regs
https://github.com/peterdelevoryas/qemu
cd qemu
./configure --target-list=arm-softmmu --disable-vnc
make -j $(nproc)
./build/arm-softmmu/qemu-system-arm \
-machine ast2600-evb \
-drive file=/tmp/fixedsize-fuji,format=raw,if=mtd \
-serial stdio
Signed-off-by: Peter Delevoryas <p...@fb.com>
---
hw/misc/aspeed_scu.c | 12 +++++++++++-
1 file changed, 11 insertions(+), 1 deletion(-)
diff --git a/hw/misc/aspeed_scu.c b/hw/misc/aspeed_scu.c
index 40a38ebd85..72b5a3afae 100644
--- a/hw/misc/aspeed_scu.c
+++ b/hw/misc/aspeed_scu.c
@@ -104,11 +104,16 @@
#define AST2600_SDRAM_HANDSHAKE TO_REG(0x100)
#define AST2600_HPLL_PARAM TO_REG(0x200)
#define AST2600_HPLL_EXT TO_REG(0x204)
+#define AST2600_APLL_PARAM TO_REG(0x210)
#define AST2600_MPLL_EXT TO_REG(0x224)
#define AST2600_EPLL_EXT TO_REG(0x244)
#define AST2600_CLK_SEL TO_REG(0x300)
#define AST2600_CLK_SEL2 TO_REG(0x304)
#define AST2600_CLK_SEL3 TO_REG(0x310)
+#define AST2600_CLK_SEL4 TO_REG(0x310)
+#define AST2600_CLK_SEL5 TO_REG(0x314)
+#define AST2600_UARTCLK_PARAM TO_REG(0x338)
+#define AST2600_HUARTCLK_PARAM TO_REG(0x33C)
#define AST2600_HW_STRAP1 TO_REG(0x500)
#define AST2600_HW_STRAP1_CLR TO_REG(0x504)
#define AST2600_HW_STRAP1_PROT TO_REG(0x508)
@@ -658,9 +663,14 @@ static const uint32_t
ast2600_a1_resets[ASPEED_AST2600_SCU_NR_REGS] = {
[AST2600_CLK_STOP_CTRL2] = 0xFFF0FFF0,
[AST2600_SDRAM_HANDSHAKE] = 0x00000000,
[AST2600_HPLL_PARAM] = 0x1000405F,
+ [AST2600_APLL_PARAM] = 0x1000405F,
[AST2600_CHIP_ID0] = 0x1234ABCD,
[AST2600_CHIP_ID1] = 0x88884444,
-
+ [AST2600_CLK_SEL2] = 0x00700000,
+ [AST2600_CLK_SEL4] = 0xF3F40000,
+ [AST2600_CLK_SEL5] = 0x30000000,
+ [AST2600_UARTCLK_PARAM] = 0x00014506,
+ [AST2600_HUARTCLK_PARAM] = 0x000145C0,
};
static void aspeed_ast2600_scu_reset(DeviceState *dev)
--
2.30.2
