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From: "Cédric Le Goater" <clg@kaod.org>
To: Peter Maydell <peter.maydell@linaro.org>
Cc: "Andrew Jeffery" <andrew@aj.id.au>,
	qemu-devel@nongnu.org, qemu-arm@nongnu.org,
	"Cédric Le Goater" <clg@kaod.org>,
	"Peter Delevoryas" <pdel@fb.com>, "Joel Stanley" <joel@jms.id.au>
Subject: [PULL 12/14] hw/arm/aspeed: Initialize AST2600 UART clock selection registers
Date: Fri, 3 Sep 2021 21:41:06 +0200	[thread overview]
Message-ID: <20210903194108.131403-13-clg@kaod.org> (raw)
In-Reply-To: <20210903194108.131403-1-clg@kaod.org>

From: Peter Delevoryas <pdel@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).

  @@ -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 <pdel@fb.com>
[ clg: - reworked diff in commit log
       - dropped CLK_SEL* changes which were already merged
       - Subject update ]
Message-Id: <20210831142502.279485-1-pdel@fb.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
---
 hw/misc/aspeed_scu.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/hw/misc/aspeed_scu.c b/hw/misc/aspeed_scu.c
index 05edebedeb46..a95dca65f2f1 100644
--- a/hw/misc/aspeed_scu.c
+++ b/hw/misc/aspeed_scu.c
@@ -119,6 +119,8 @@
 #define AST2600_CLK_SEL3          TO_REG(0x308)
 #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)
@@ -681,6 +683,8 @@ static const uint32_t ast2600_a3_resets[ASPEED_AST2600_SCU_NR_REGS] = {
     [AST2600_CLK_SEL3]          = 0x00000000,
     [AST2600_CLK_SEL4]          = 0xF3F40000,
     [AST2600_CLK_SEL5]          = 0x30000000,
+    [AST2600_UARTCLK_PARAM]     = 0x00014506,
+    [AST2600_HUARTCLK_PARAM]    = 0x000145C0,
     [AST2600_CHIP_ID0]          = 0x1234ABCD,
     [AST2600_CHIP_ID1]          = 0x88884444,
 };
-- 
2.31.1



  parent reply	other threads:[~2021-09-03 19:48 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-03 19:40 [PULL 00/14] aspeed queue Cédric Le Goater
2021-09-03 19:40 ` [PULL 01/14] hw: arm: aspeed: Enable eth0 interface for aspeed-ast2600-evb Cédric Le Goater
2021-09-03 19:40 ` [PULL 02/14] hw: arm: aspeed: Enable mac0/1 instead of mac1/2 for g220a Cédric Le Goater
2021-09-03 19:40 ` [PULL 03/14] watchdog: aspeed: Sanitize control register values Cédric Le Goater
2021-09-03 19:40 ` [PULL 04/14] watchdog: aspeed: Fix sequential control writes Cédric Le Goater
2021-09-03 19:40 ` [PULL 05/14] hw: aspeed_gpio: Simplify 1.8V defines Cédric Le Goater
2021-09-03 19:41 ` [PULL 06/14] hw: aspeed_gpio: Clarify GPIO controller name Cédric Le Goater
2021-09-03 19:41 ` [PULL 07/14] misc/pca9552: Fix LED status register indexing in pca955x_get_led() Cédric Le Goater
2021-09-03 19:41 ` [PULL 08/14] arm/aspeed: rainier: Add i2c eeproms and muxes Cédric Le Goater
2021-09-03 19:41 ` [PULL 09/14] aspeed: Emulate the AST2600A3 Cédric Le Goater
2021-09-03 19:41 ` [PULL 10/14] hw/misc: Add Infineon DPS310 sensor model Cédric Le Goater
2021-09-03 19:41 ` [PULL 11/14] arm/aspeed: Add DPS310 to Witherspoon and Rainier Cédric Le Goater
2021-09-03 19:41 ` Cédric Le Goater [this message]
2021-09-03 19:41 ` [PULL 13/14] hw/arm/aspeed: Allow machine to set UART default Cédric Le Goater
2021-09-03 19:41 ` [PULL 14/14] hw/arm/aspeed: Add Fuji machine type Cédric Le Goater
2021-09-03 20:39   ` Philippe Mathieu-Daudé
2021-09-03 20:41 ` [PULL 00/14] aspeed queue Philippe Mathieu-Daudé
2021-09-04  5:33   ` Cédric Le Goater
2021-09-04 23:03     ` Philippe Mathieu-Daudé
2021-09-05  8:51       ` Cédric Le Goater
2021-09-05 14:34         ` Peter Delevoryas
2021-09-05 14:43           ` Cédric Le Goater
2021-09-13 16:12 Cédric Le Goater
2021-09-13 16:13 ` [PULL 12/14] hw/arm/aspeed: Initialize AST2600 UART clock selection registers Cédric Le Goater
2021-09-20  8:09 [PULL 00/14] aspeed queue Cédric Le Goater
2021-09-20  8:09 ` [PULL 12/14] hw/arm/aspeed: Initialize AST2600 UART clock selection registers Cédric Le Goater

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