Re: [PATCH v2 4/9] powerpc/powernv: OPAL console standardise OPAL_BUSY loops

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2018-04-09 at 15:24 +1000, Nicholas Piggin wrote:
> Convert to using the standard delay poll/delay form.
> 
> The console code:
> 
> - Did not previously delay or sleep in its busy loop.
> 
> Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
> Signed-off-by: Nicholas Piggin <npiggin@gmail.com>

Does it help with anything ? We don't technically *have* to delay or
wait, I thought it would be good to try to hit the console as fast as
possible in that case...

Ben.

> ---
>  arch/powerpc/platforms/powernv/opal.c | 38 ++++++++++++++++-----------
>  1 file changed, 23 insertions(+), 15 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
> index 87d4c0aa7f64..473c8ce14a34 100644
> --- a/arch/powerpc/platforms/powernv/opal.c
> +++ b/arch/powerpc/platforms/powernv/opal.c
> @@ -378,33 +378,41 @@ int opal_put_chars(uint32_t vtermno, const char *data, int total_len)
>  	/* We still try to handle partial completions, though they
>  	 * should no longer happen.
>  	 */
> -	rc = OPAL_BUSY;
> -	while(total_len > 0 && (rc == OPAL_BUSY ||
> -				rc == OPAL_BUSY_EVENT || rc == OPAL_SUCCESS)) {
> +
> +	while (total_len > 0) {
>  		olen = cpu_to_be64(total_len);
> -		rc = opal_console_write(vtermno, &olen, data);
> +
> +		rc = OPAL_BUSY;
> +		while (rc == OPAL_BUSY || rc == OPAL_BUSY_EVENT) {
> +			rc = opal_console_write(vtermno, &olen, data);
> +			if (rc == OPAL_BUSY_EVENT) {
> +				mdelay(OPAL_BUSY_DELAY_MS);
> +				opal_poll_events(NULL);
> +			} else if (rc == OPAL_BUSY) {
> +				mdelay(OPAL_BUSY_DELAY_MS);
> +			}
> +		}
> +
>  		len = be64_to_cpu(olen);
>  
>  		/* Closed or other error drop */
> -		if (rc != OPAL_SUCCESS && rc != OPAL_BUSY &&
> -		    rc != OPAL_BUSY_EVENT) {
> -			written += total_len;
> +		if (rc != OPAL_SUCCESS) {
> +			written += total_len; /* drop remaining chars */
>  			break;
>  		}
> -		if (rc == OPAL_SUCCESS) {
> -			total_len -= len;
> -			data += len;
> -			written += len;
> -		}
> +
> +		total_len -= len;
> +		data += len;
> +		written += len;
> +
>  		/* This is a bit nasty but we need that for the console to
>  		 * flush when there aren't any interrupts. We will clean
>  		 * things a bit later to limit that to synchronous path
>  		 * such as the kernel console and xmon/udbg
>  		 */
> -		do
> +		do {
>  			opal_poll_events(&evt);
> -		while(rc == OPAL_SUCCESS &&
> -			(be64_to_cpu(evt) & OPAL_EVENT_CONSOLE_OUTPUT));
> +		} while (be64_to_cpu(evt) & OPAL_EVENT_CONSOLE_OUTPUT);
>  	}
>  	spin_unlock_irqrestore(&opal_write_lock, flags);
>  	return written;