Re: [PATCH v6 8/9] hw/char/cadence_uart: add clock support

[Peter Maydell <peter.maydell@linaro.org>]

On Wed, 4 Sep 2019 at 13:56, Damien Hedde <damien.hedde@greensocs.com> wrote:
>
> Switch the cadence uart to multi-phase reset and add the
> reference clock input.
>
> The input clock frequency is added to the migration structure.
>
> The reference clock controls the baudrate generation. If it disabled,
> any input characters and events are ignored.
>
> If this clock remains unconnected, the uart behaves as before
> (it default to a 50MHz ref clock).
>
> Signed-off-by: Damien Hedde <damien.hedde@greensocs.com>

>  static void uart_parameters_setup(CadenceUARTState *s)
>  {
>      QEMUSerialSetParams ssp;
> -    unsigned int baud_rate, packet_size;
> +    unsigned int baud_rate, packet_size, input_clk;
> +    input_clk = clock_get_frequency(s->refclk);
>
> -    baud_rate = (s->r[R_MR] & UART_MR_CLKS) ?
> -            UART_INPUT_CLK / 8 : UART_INPUT_CLK;
> +    baud_rate = (s->r[R_MR] & UART_MR_CLKS) ? input_clk / 8 : input_clk;
> +    baud_rate /= (s->r[R_BRGR] * (s->r[R_BDIV] + 1));
> +    trace_cadence_uart_baudrate(baud_rate);
> +
> +    ssp.speed = baud_rate;
>
> -    ssp.speed = baud_rate / (s->r[R_BRGR] * (s->r[R_BDIV] + 1));
>      packet_size = 1;
>
>      switch (s->r[R_MR] & UART_MR_PAR) {
> @@ -215,6 +220,13 @@ static void uart_parameters_setup(CadenceUARTState *s)
>      }
>
>      packet_size += ssp.data_bits + ssp.stop_bits;
> +    if (ssp.speed == 0) {
> +        /*
> +         * Avoid division-by-zero below.
> +         * TODO: find something better
> +         */

Any ideas what might be better? :-)

> +        ssp.speed = 1;
> +    }
>      s->char_tx_time = (NANOSECONDS_PER_SECOND / ssp.speed) * packet_size;
>      qemu_chr_fe_ioctl(&s->chr, CHR_IOCTL_SERIAL_SET_PARAMS, &ssp);
>  }

thanks
-- PMM