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Re: [PATCH 2/3] hw/char: cadence_uart: Disable transmit when input clock
From: |
Alistair Francis |
Subject: |
Re: [PATCH 2/3] hw/char: cadence_uart: Disable transmit when input clock is disabled |
Date: |
Mon, 23 Aug 2021 16:52:48 +1000 |
On Mon, Aug 23, 2021 at 2:53 PM Bin Meng <bmeng.cn@gmail.com> wrote:
>
> On Mon, Aug 23, 2021 at 12:43 PM Alistair Francis <alistair23@gmail.com>
> wrote:
> >
> > On Mon, Aug 23, 2021 at 12:11 PM Bin Meng <bmeng.cn@gmail.com> wrote:
> > >
> > > 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>
> > > ---
> > >
> > > 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;
> > > + }
> >
> > Should we log a guest error here?
> >
>
> Not sure. Based on my past experience of many hardware, if the input
> clock is disabled, accessing the whole register block might cause a
> bus fault. But I believe such bus fault is not modeled in QEMU.
>
> This change just mirrors the same check on the Rx side.
Ok:
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Alistair
>
> Regards,
> Bin
[PATCH 3/3] hw/char: cadence_uart: Move clock/reset check to uart_can_receive(), Bin Meng, 2021/08/22