Re: [Xen-devel] [PATCH] drivers/exynos4210: Wait the end of last transfer before initializing the UART

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Wed, 2013-05-22 at 12:50 +0100, Julien Grall wrote:
> When early printk is enabled by the user, it's possible to loose the last
> characters if the UART is initialized without waiting that the last transfer
> was completed.

It might actually be useful to do this in early_printk, i.e. a new
early_uart_flush or so called from puts and early_puts (or even just
from the putch hook).

Any opinions?

Perhaps we should take this fix as is for 4.3 and look at the
alternatives for 4.4?


> Signed-off-by: Julien Grall <julien.grall@xxxxxxxxxx>
> ---
>  xen/drivers/char/exynos4210-uart.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/xen/drivers/char/exynos4210-uart.c 
> b/xen/drivers/char/exynos4210-uart.c
> index f7971da..13758d4 100644
> --- a/xen/drivers/char/exynos4210-uart.c
> +++ b/xen/drivers/char/exynos4210-uart.c
> @@ -104,6 +104,12 @@ static void __init exynos4210_uart_init_preirq(struct 
> serial_port *port)
>      unsigned int divisor;
>      uint32_t ulcon;
>  
> +#ifdef EARLY_PRINTK
> +    /* Flush the UART */
> +    while ( !(exynos4210_read(uart, UTRSTAT) &  UTRSTAT_TX_EMPTY) )
> +        cpu_relax();
> +#endif
> +
>      /* reset, TX/RX disables */
>      exynos4210_write(uart, UCON, 0);
>  



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