[PATCH v2 0/5] hw/arm: xilinx_zynq: Fix upstream U-Boot boot failure

[PATCH v2 0/5] hw/arm: xilinx_zynq: Fix upstream U-Boot boot failure

[Bin Meng]

As of today, when booting upstream U-Boot for Xilinx Zynq, the UART
does not receive anything. Debugging shows that the UART input clock
frequency is zero which prevents the UART from receiving anything as.
per the logic in uart_receive().

Note the U-Boot can still output data to the UART tx fifo, which should
not happen, as the design seems to prevent the data transmission when
clock is not enabled but somehow it only applies to the Rx side.

For anyone who is interested to give a try, here is the U-Boot defconfig:
$ make xilinx_zynq_virt_defconfig

and QEMU commands to test U-Boot:
$ qemu-system-arm -M xilinx-zynq-a9 -m 1G -display none -serial null -serial stdio \
    -device loader,file=u-boot-dtb.bin,addr=0x4000000,cpu-num=0

Note U-Boot used to boot properly in QEMU 4.2.0 which is the QEMU
version used in current U-Boot's CI testing. The UART clock changes
were introduced by the following 3 commits:

38867cb7ec90 ("hw/misc/zynq_slcr: add clock generation for uarts")
b636db306e06 ("hw/char/cadence_uart: add clock support")
5b49a34c6800 ("hw/arm/xilinx_zynq: connect uart clocks to slcr")

Changes in v2:
- avoid declaring variables mid-scope
- new patch: hw/char: cadence_uart: Convert to memop_with_attrs() ops
- new patch: hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()

Bin Meng (5):
  hw/misc: zynq_slcr: Correctly compute output clocks in the reset exit
    phase
  hw/char: cadence_uart: Disable transmit when input clock is disabled
  hw/char: cadence_uart: Move clock/reset check to uart_can_receive()
  hw/char: cadence_uart: Convert to memop_with_attrs() ops
  hw/char: cadence_uart: Ignore access when unclocked or in reset for
    uart_{read,write}()

 hw/char/cadence_uart.c | 53 ++++++++++++++++++++++++++++--------------
 hw/misc/zynq_slcr.c    | 31 +++++++++++++-----------
 2 files changed, 53 insertions(+), 31 deletions(-)

-- 
2.25.1

[PATCH v2 1/5] hw/misc: zynq_slcr: Correctly compute output clocks in the reset exit phase

[Bin Meng]

As of today, when booting upstream U-Boot for Xilinx Zynq, the UART
does not receive anything. Debugging shows that the UART input clock
frequency is zero which prevents the UART from receiving anything as
per the logic in uart_receive().

From zynq_slcr_reset_exit() comment, it intends to compute output
clocks according to ps_clk and registers. zynq_slcr_compute_clocks()
is called to accomplish the task, inside which device_is_in_reset()
is called to actually make the attempt in vain.

Rework reset_hold() and reset_exit() so that in the reset exit phase,
the logic can really compute output clocks in reset_exit().

With this change, upstream U-Boot boots properly again with:

$ qemu-system-arm -M xilinx-zynq-a9 -m 1G -display none -serial null -serial stdio \
    -device loader,file=u-boot-dtb.bin,addr=0x4000000,cpu-num=0

Fixes: 38867cb7ec90 ("hw/misc/zynq_slcr: add clock generation for uarts")
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
---

(no changes since v1)

 hw/misc/zynq_slcr.c | 31 ++++++++++++++++++-------------
 1 file changed, 18 insertions(+), 13 deletions(-)

diff --git a/hw/misc/zynq_slcr.c b/hw/misc/zynq_slcr.c
index 5086e6b7ed..8b70285961 100644
--- a/hw/misc/zynq_slcr.c
+++ b/hw/misc/zynq_slcr.c
@@ -269,6 +269,21 @@ static uint64_t zynq_slcr_compute_clock(const uint64_t periods[],
     zynq_slcr_compute_clock((plls), (state)->regs[reg], \
                             reg ## _ ## enable_field ## _SHIFT)
 
+static void zynq_slcr_compute_clocks_internal(ZynqSLCRState *s, uint64_t ps_clk)
+{
+    uint64_t io_pll = zynq_slcr_compute_pll(ps_clk, s->regs[R_IO_PLL_CTRL]);
+    uint64_t arm_pll = zynq_slcr_compute_pll(ps_clk, s->regs[R_ARM_PLL_CTRL]);
+    uint64_t ddr_pll = zynq_slcr_compute_pll(ps_clk, s->regs[R_DDR_PLL_CTRL]);
+
+    uint64_t uart_mux[4] = {io_pll, io_pll, arm_pll, ddr_pll};
+
+    /* compute uartX reference clocks */
+    clock_set(s->uart0_ref_clk,
+              ZYNQ_COMPUTE_CLK(s, uart_mux, R_UART_CLK_CTRL, CLKACT0));
+    clock_set(s->uart1_ref_clk,
+              ZYNQ_COMPUTE_CLK(s, uart_mux, R_UART_CLK_CTRL, CLKACT1));
+}
+
 /**
  * Compute and set the ouputs clocks periods.
  * But do not propagate them further. Connected clocks
@@ -283,17 +298,7 @@ static void zynq_slcr_compute_clocks(ZynqSLCRState *s)
         ps_clk = 0;
     }
 
-    uint64_t io_pll = zynq_slcr_compute_pll(ps_clk, s->regs[R_IO_PLL_CTRL]);
-    uint64_t arm_pll = zynq_slcr_compute_pll(ps_clk, s->regs[R_ARM_PLL_CTRL]);
-    uint64_t ddr_pll = zynq_slcr_compute_pll(ps_clk, s->regs[R_DDR_PLL_CTRL]);
-
-    uint64_t uart_mux[4] = {io_pll, io_pll, arm_pll, ddr_pll};
-
-    /* compute uartX reference clocks */
-    clock_set(s->uart0_ref_clk,
-              ZYNQ_COMPUTE_CLK(s, uart_mux, R_UART_CLK_CTRL, CLKACT0));
-    clock_set(s->uart1_ref_clk,
-              ZYNQ_COMPUTE_CLK(s, uart_mux, R_UART_CLK_CTRL, CLKACT1));
+    zynq_slcr_compute_clocks_internal(s, ps_clk);
 }
 
 /**
@@ -416,7 +421,7 @@ static void zynq_slcr_reset_hold(Object *obj)
     ZynqSLCRState *s = ZYNQ_SLCR(obj);
 
     /* will disable all output clocks */
-    zynq_slcr_compute_clocks(s);
+    zynq_slcr_compute_clocks_internal(s, 0);
     zynq_slcr_propagate_clocks(s);
 }
 
@@ -425,7 +430,7 @@ static void zynq_slcr_reset_exit(Object *obj)
     ZynqSLCRState *s = ZYNQ_SLCR(obj);
 
     /* will compute output clocks according to ps_clk and registers */
-    zynq_slcr_compute_clocks(s);
+    zynq_slcr_compute_clocks_internal(s, clock_get(s->ps_clk));
     zynq_slcr_propagate_clocks(s);
 }
 
-- 
2.25.1

[PATCH v2 2/5] hw/char: cadence_uart: Disable transmit when input clock is disabled

[Bin Meng]

At present when input clock is disabled, any character transmitted
to tx fifo can still show on the serial line, which is wrong.

Fixes: b636db306e06 ("hw/char/cadence_uart: add clock support")
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
---

(no changes since v1)

 hw/char/cadence_uart.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index b4b5e8a3ee..154be34992 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -327,6 +327,11 @@ static gboolean cadence_uart_xmit(void *do_not_use, GIOCondition cond,
 static void uart_write_tx_fifo(CadenceUARTState *s, const uint8_t *buf,
                                int size)
 {
+    /* ignore characters when unclocked or in reset */
+    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
+        return;
+    }
+
     if ((s->r[R_CR] & UART_CR_TX_DIS) || !(s->r[R_CR] & UART_CR_TX_EN)) {
         return;
     }
-- 
2.25.1

[PATCH v2 3/5] hw/char: cadence_uart: Move clock/reset check to uart_can_receive()

[Bin Meng]

Currently the clock/reset check is done in uart_receive(), but we
can move the check to uart_can_receive() which is earlier.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

---

Changes in v2:
- avoid declaring variables mid-scope

 hw/char/cadence_uart.c | 17 ++++++++++-------
 1 file changed, 10 insertions(+), 7 deletions(-)

diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index 154be34992..fff8be3619 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -235,8 +235,16 @@ static void uart_parameters_setup(CadenceUARTState *s)
 static int uart_can_receive(void *opaque)
 {
     CadenceUARTState *s = opaque;
-    int ret = MAX(CADENCE_UART_RX_FIFO_SIZE, CADENCE_UART_TX_FIFO_SIZE);
-    uint32_t ch_mode = s->r[R_MR] & UART_MR_CHMODE;
+    int ret;
+    uint32_t ch_mode;
+
+    /* ignore characters when unclocked or in reset */
+    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
+        return 0;
+    }
+
+    ret = MAX(CADENCE_UART_RX_FIFO_SIZE, CADENCE_UART_TX_FIFO_SIZE);
+    ch_mode = s->r[R_MR] & UART_MR_CHMODE;
 
     if (ch_mode == NORMAL_MODE || ch_mode == ECHO_MODE) {
         ret = MIN(ret, CADENCE_UART_RX_FIFO_SIZE - s->rx_count);
@@ -358,11 +366,6 @@ static void uart_receive(void *opaque, const uint8_t *buf, int size)
     CadenceUARTState *s = opaque;
     uint32_t ch_mode = s->r[R_MR] & UART_MR_CHMODE;
 
-    /* ignore characters when unclocked or in reset */
-    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
-        return;
-    }
-
     if (ch_mode == NORMAL_MODE || ch_mode == ECHO_MODE) {
         uart_write_rx_fifo(opaque, buf, size);
     }
-- 
2.25.1

Re: [PATCH v2 3/5] hw/char: cadence_uart: Move clock/reset check to uart_can_receive()

[Alistair Francis]

On Wed, Sep 1, 2021 at 1:28 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> Currently the clock/reset check is done in uart_receive(), but we
> can move the check to uart_can_receive() which is earlier.
>
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

>
> ---
>
> Changes in v2:
> - avoid declaring variables mid-scope
>
>  hw/char/cadence_uart.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
> index 154be34992..fff8be3619 100644
> --- a/hw/char/cadence_uart.c
> +++ b/hw/char/cadence_uart.c
> @@ -235,8 +235,16 @@ static void uart_parameters_setup(CadenceUARTState *s)
>  static int uart_can_receive(void *opaque)
>  {
>      CadenceUARTState *s = opaque;
> -    int ret = MAX(CADENCE_UART_RX_FIFO_SIZE, CADENCE_UART_TX_FIFO_SIZE);
> -    uint32_t ch_mode = s->r[R_MR] & UART_MR_CHMODE;
> +    int ret;
> +    uint32_t ch_mode;
> +
> +    /* ignore characters when unclocked or in reset */
> +    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
> +        return 0;
> +    }
> +
> +    ret = MAX(CADENCE_UART_RX_FIFO_SIZE, CADENCE_UART_TX_FIFO_SIZE);
> +    ch_mode = s->r[R_MR] & UART_MR_CHMODE;
>
>      if (ch_mode == NORMAL_MODE || ch_mode == ECHO_MODE) {
>          ret = MIN(ret, CADENCE_UART_RX_FIFO_SIZE - s->rx_count);
> @@ -358,11 +366,6 @@ static void uart_receive(void *opaque, const uint8_t *buf, int size)
>      CadenceUARTState *s = opaque;
>      uint32_t ch_mode = s->r[R_MR] & UART_MR_CHMODE;
>
> -    /* ignore characters when unclocked or in reset */
> -    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
> -        return;
> -    }
> -
>      if (ch_mode == NORMAL_MODE || ch_mode == ECHO_MODE) {
>          uart_write_rx_fifo(opaque, buf, size);
>      }
> --
> 2.25.1
>
>

Re: [PATCH v2 3/5] hw/char: cadence_uart: Move clock/reset check to uart_can_receive()

[Philippe Mathieu-Daudé]

On 9/1/21 5:27 AM, Bin Meng wrote:
> Currently the clock/reset check is done in uart_receive(), but we
> can move the check to uart_can_receive() which is earlier.
> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> 
> ---
> 
> Changes in v2:
> - avoid declaring variables mid-scope
> 
>  hw/char/cadence_uart.c | 17 ++++++++++-------
>  1 file changed, 10 insertions(+), 7 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

[PATCH v2 4/5] hw/char: cadence_uart: Convert to memop_with_attrs() ops

[Bin Meng]

This converts uart_read() and uart_write() to memop_with_attrs() ops.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

---

Changes in v2:
- new patch: hw/char: cadence_uart: Convert to memop_with_attrs() ops

 hw/char/cadence_uart.c | 26 +++++++++++++++-----------
 1 file changed, 15 insertions(+), 11 deletions(-)

diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index fff8be3619..8bcf2b718a 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -411,15 +411,15 @@ static void uart_read_rx_fifo(CadenceUARTState *s, uint32_t *c)
     uart_update_status(s);
 }
 
-static void uart_write(void *opaque, hwaddr offset,
-                          uint64_t value, unsigned size)
+static MemTxResult uart_write(void *opaque, hwaddr offset,
+                              uint64_t value, unsigned size, MemTxAttrs attrs)
 {
     CadenceUARTState *s = opaque;
 
     DB_PRINT(" offset:%x data:%08x\n", (unsigned)offset, (unsigned)value);
     offset >>= 2;
     if (offset >= CADENCE_UART_R_MAX) {
-        return;
+        return MEMTX_DECODE_ERROR;
     }
     switch (offset) {
     case R_IER: /* ier (wts imr) */
@@ -466,30 +466,34 @@ static void uart_write(void *opaque, hwaddr offset,
         break;
     }
     uart_update_status(s);
+
+    return MEMTX_OK;
 }
 
-static uint64_t uart_read(void *opaque, hwaddr offset,
-        unsigned size)
+static MemTxResult uart_read(void *opaque, hwaddr offset,
+                             uint64_t *value, unsigned size, MemTxAttrs attrs)
 {
     CadenceUARTState *s = opaque;
     uint32_t c = 0;
 
     offset >>= 2;
     if (offset >= CADENCE_UART_R_MAX) {
-        c = 0;
-    } else if (offset == R_TX_RX) {
+        return MEMTX_DECODE_ERROR;
+    }
+    if (offset == R_TX_RX) {
         uart_read_rx_fifo(s, &c);
     } else {
-       c = s->r[offset];
+        c = s->r[offset];
     }
 
     DB_PRINT(" offset:%x data:%08x\n", (unsigned)(offset << 2), (unsigned)c);
-    return c;
+    *value = c;
+    return MEMTX_OK;
 }
 
 static const MemoryRegionOps uart_ops = {
-    .read = uart_read,
-    .write = uart_write,
+    .read_with_attrs = uart_read,
+    .write_with_attrs = uart_write,
     .endianness = DEVICE_NATIVE_ENDIAN,
 };
 
-- 
2.25.1

Re: [PATCH v2 4/5] hw/char: cadence_uart: Convert to memop_with_attrs() ops

[Alistair Francis]

On Wed, Sep 1, 2021 at 1:30 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> This converts uart_read() and uart_write() to memop_with_attrs() ops.
>
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>

Alistair

>
> ---
>
> Changes in v2:
> - new patch: hw/char: cadence_uart: Convert to memop_with_attrs() ops
>
>  hw/char/cadence_uart.c | 26 +++++++++++++++-----------
>  1 file changed, 15 insertions(+), 11 deletions(-)
>
> diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
> index fff8be3619..8bcf2b718a 100644
> --- a/hw/char/cadence_uart.c
> +++ b/hw/char/cadence_uart.c
> @@ -411,15 +411,15 @@ static void uart_read_rx_fifo(CadenceUARTState *s, uint32_t *c)
>      uart_update_status(s);
>  }
>
> -static void uart_write(void *opaque, hwaddr offset,
> -                          uint64_t value, unsigned size)
> +static MemTxResult uart_write(void *opaque, hwaddr offset,
> +                              uint64_t value, unsigned size, MemTxAttrs attrs)
>  {
>      CadenceUARTState *s = opaque;
>
>      DB_PRINT(" offset:%x data:%08x\n", (unsigned)offset, (unsigned)value);
>      offset >>= 2;
>      if (offset >= CADENCE_UART_R_MAX) {
> -        return;
> +        return MEMTX_DECODE_ERROR;
>      }
>      switch (offset) {
>      case R_IER: /* ier (wts imr) */
> @@ -466,30 +466,34 @@ static void uart_write(void *opaque, hwaddr offset,
>          break;
>      }
>      uart_update_status(s);
> +
> +    return MEMTX_OK;
>  }
>
> -static uint64_t uart_read(void *opaque, hwaddr offset,
> -        unsigned size)
> +static MemTxResult uart_read(void *opaque, hwaddr offset,
> +                             uint64_t *value, unsigned size, MemTxAttrs attrs)
>  {
>      CadenceUARTState *s = opaque;
>      uint32_t c = 0;
>
>      offset >>= 2;
>      if (offset >= CADENCE_UART_R_MAX) {
> -        c = 0;
> -    } else if (offset == R_TX_RX) {
> +        return MEMTX_DECODE_ERROR;
> +    }
> +    if (offset == R_TX_RX) {
>          uart_read_rx_fifo(s, &c);
>      } else {
> -       c = s->r[offset];
> +        c = s->r[offset];
>      }
>
>      DB_PRINT(" offset:%x data:%08x\n", (unsigned)(offset << 2), (unsigned)c);
> -    return c;
> +    *value = c;
> +    return MEMTX_OK;
>  }
>
>  static const MemoryRegionOps uart_ops = {
> -    .read = uart_read,
> -    .write = uart_write,
> +    .read_with_attrs = uart_read,
> +    .write_with_attrs = uart_write,
>      .endianness = DEVICE_NATIVE_ENDIAN,
>  };
>
> --
> 2.25.1
>
>

[PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read, write}()

[Bin Meng]

Read or write to uart registers when unclocked or in reset should be
ignored. Add the check there, and as a result of this, the check in
uart_write_tx_fifo() is now unnecessary.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>

---

Changes in v2:
- new patch: hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()

 hw/char/cadence_uart.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
index 8bcf2b718a..5f5a4645ac 100644
--- a/hw/char/cadence_uart.c
+++ b/hw/char/cadence_uart.c
@@ -335,11 +335,6 @@ static gboolean cadence_uart_xmit(void *do_not_use, GIOCondition cond,
 static void uart_write_tx_fifo(CadenceUARTState *s, const uint8_t *buf,
                                int size)
 {
-    /* ignore characters when unclocked or in reset */
-    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
-        return;
-    }
-
     if ((s->r[R_CR] & UART_CR_TX_DIS) || !(s->r[R_CR] & UART_CR_TX_EN)) {
         return;
     }
@@ -416,6 +411,11 @@ static MemTxResult uart_write(void *opaque, hwaddr offset,
 {
     CadenceUARTState *s = opaque;
 
+    /* ignore access when unclocked or in reset */
+    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
+        return MEMTX_ERROR;
+    }
+
     DB_PRINT(" offset:%x data:%08x\n", (unsigned)offset, (unsigned)value);
     offset >>= 2;
     if (offset >= CADENCE_UART_R_MAX) {
@@ -476,6 +476,11 @@ static MemTxResult uart_read(void *opaque, hwaddr offset,
     CadenceUARTState *s = opaque;
     uint32_t c = 0;
 
+    /* ignore access when unclocked or in reset */
+    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
+        return MEMTX_ERROR;
+    }
+
     offset >>= 2;
     if (offset >= CADENCE_UART_R_MAX) {
         return MEMTX_DECODE_ERROR;
-- 
2.25.1

Re: [PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()

[Edgar E. Iglesias]

On Wed, Sep 01, 2021 at 11:27:24AM +0800, Bin Meng wrote:
> Read or write to uart registers when unclocked or in reset should be
> ignored. Add the check there, and as a result of this, the check in
> uart_write_tx_fifo() is now unnecessary.

Hi Bin,

I thought I had replied to this but it must have gotten lost somewhere.

We've got SW that expects FSBL (Bootlooader) to setup clocks and resets.
It's quite common that users run that SW on QEMU without FSBL (FSBL typically
requires the Xilinx tools installed). That's fine, since users can stil use
-device loader to enable clocks etc.

To help folks understand what's going, a log (guest-error) message would
be helpful here. In particular with the serial port since things will go
very quiet if they get things wrong.

Otherwise, this patch is fine with me.

Thanks,
Edgar


> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> 
> ---
> 
> Changes in v2:
> - new patch: hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()
> 
>  hw/char/cadence_uart.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> diff --git a/hw/char/cadence_uart.c b/hw/char/cadence_uart.c
> index 8bcf2b718a..5f5a4645ac 100644
> --- a/hw/char/cadence_uart.c
> +++ b/hw/char/cadence_uart.c
> @@ -335,11 +335,6 @@ static gboolean cadence_uart_xmit(void *do_not_use, GIOCondition cond,
>  static void uart_write_tx_fifo(CadenceUARTState *s, const uint8_t *buf,
>                                 int size)
>  {
> -    /* ignore characters when unclocked or in reset */
> -    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
> -        return;
> -    }
> -
>      if ((s->r[R_CR] & UART_CR_TX_DIS) || !(s->r[R_CR] & UART_CR_TX_EN)) {
>          return;
>      }
> @@ -416,6 +411,11 @@ static MemTxResult uart_write(void *opaque, hwaddr offset,
>  {
>      CadenceUARTState *s = opaque;
>  
> +    /* ignore access when unclocked or in reset */
> +    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
> +        return MEMTX_ERROR;
> +    }
> +
>      DB_PRINT(" offset:%x data:%08x\n", (unsigned)offset, (unsigned)value);
>      offset >>= 2;
>      if (offset >= CADENCE_UART_R_MAX) {
> @@ -476,6 +476,11 @@ static MemTxResult uart_read(void *opaque, hwaddr offset,
>      CadenceUARTState *s = opaque;
>      uint32_t c = 0;
>  
> +    /* ignore access when unclocked or in reset */
> +    if (!clock_is_enabled(s->refclk) || device_is_in_reset(DEVICE(s))) {
> +        return MEMTX_ERROR;
> +    }
> +
>      offset >>= 2;
>      if (offset >= CADENCE_UART_R_MAX) {
>          return MEMTX_DECODE_ERROR;
> -- 
> 2.25.1
> 

Re: [PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()

[Bin Meng]

Hi Edgar,

On Wed, Sep 1, 2021 at 4:32 PM Edgar E. Iglesias
<edgar.iglesias@xilinx.com> wrote:
>
> On Wed, Sep 01, 2021 at 11:27:24AM +0800, Bin Meng wrote:
> > Read or write to uart registers when unclocked or in reset should be
> > ignored. Add the check there, and as a result of this, the check in
> > uart_write_tx_fifo() is now unnecessary.
>
> Hi Bin,
>
> I thought I had replied to this but it must have gotten lost somewhere.
>
> We've got SW that expects FSBL (Bootlooader) to setup clocks and resets.
> It's quite common that users run that SW on QEMU without FSBL (FSBL typically
> requires the Xilinx tools installed). That's fine, since users can stil use
> -device loader to enable clocks etc.
>
> To help folks understand what's going, a log (guest-error) message would
> be helpful here. In particular with the serial port since things will go
> very quiet if they get things wrong.
>
> Otherwise, this patch is fine with me.
>

Thanks. Will add a separate patch to enable a log message for all places.

Regards,
Bin

Re: [PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()

[Philippe Mathieu-Daudé]

On 9/1/21 10:32 AM, Edgar E. Iglesias wrote:
> On Wed, Sep 01, 2021 at 11:27:24AM +0800, Bin Meng wrote:
>> Read or write to uart registers when unclocked or in reset should be
>> ignored. Add the check there, and as a result of this, the check in
>> uart_write_tx_fifo() is now unnecessary.
> 
> Hi Bin,
> 
> I thought I had replied to this but it must have gotten lost somewhere.
> 
> We've got SW that expects FSBL (Bootlooader) to setup clocks and resets.
> It's quite common that users run that SW on QEMU without FSBL (FSBL typically
> requires the Xilinx tools installed). That's fine, since users can stil use
> -device loader to enable clocks etc.
> 
> To help folks understand what's going, a log (guest-error) message would
> be helpful here. In particular with the serial port since things will go
> very quiet if they get things wrong.

Interesting, I was expecting this error to be reported by
memory_region_access_valid() but indeed it is not in the path.

Alternative is to implement MemoryRegionOps::accepts().

Re: [PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read, write}()

[Philippe Mathieu-Daudé]

On 9/1/21 5:27 AM, Bin Meng wrote:
> Read or write to uart registers when unclocked or in reset should be
> ignored. Add the check there, and as a result of this, the check in
> uart_write_tx_fifo() is now unnecessary.
> 
> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> 
> ---
> 
> Changes in v2:
> - new patch: hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()
> 
>  hw/char/cadence_uart.c | 15 ++++++++++-----
>  1 file changed, 10 insertions(+), 5 deletions(-)

Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Re: [PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read, write}()

[Philippe Mathieu-Daudé]

On 9/2/21 8:09 AM, Philippe Mathieu-Daudé wrote:
> On 9/1/21 5:27 AM, Bin Meng wrote:
>> Read or write to uart registers when unclocked or in reset should be
>> ignored. Add the check there, and as a result of this, the check in
>> uart_write_tx_fifo() is now unnecessary.
>>
>> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
>>
>> ---
>>
>> Changes in v2:
>> - new patch: hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()
>>
>>  hw/char/cadence_uart.c | 15 ++++++++++-----
>>  1 file changed, 10 insertions(+), 5 deletions(-)
> 
> Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>

Just realized it is simpler to implement MemoryRegionOps::accepts().

Re: [PATCH v2 5/5] hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read, write}()

[Bin Meng]

On Thu, Sep 2, 2021 at 2:11 PM Philippe Mathieu-Daudé <f4bug@amsat.org> wrote:
>
> On 9/2/21 8:09 AM, Philippe Mathieu-Daudé wrote:
> > On 9/1/21 5:27 AM, Bin Meng wrote:
> >> Read or write to uart registers when unclocked or in reset should be
> >> ignored. Add the check there, and as a result of this, the check in
> >> uart_write_tx_fifo() is now unnecessary.
> >>
> >> Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
> >>
> >> ---
> >>
> >> Changes in v2:
> >> - new patch: hw/char: cadence_uart: Ignore access when unclocked or in reset for uart_{read,write}()
> >>
> >>  hw/char/cadence_uart.c | 15 ++++++++++-----
> >>  1 file changed, 10 insertions(+), 5 deletions(-)
> >
> > Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
>
> Just realized it is simpler to implement MemoryRegionOps::accepts().

Is there any guidance on what condition falls into
MemoryRegionOps::accepts() to check?

For example, should we move the register offset check to accepts()?

It looks like only a few codes implemented the MemoryRegionOps::accepts().

Regards,
Bin