[PATCH 7/8] serial: imx: use readl() to optimize FIFO reading loop

[Uwe Kleine-König]

On Fri, Jan 13, 2023 at 09:43:33PM +0300, Sergey Organov wrote:
> Use readl() instead of heavier imx_uart_readl() in the Rx ISR, as we know
> we read registers that must not be cached.
> 
> Signed-off-by: Sergey Organov <sorganov at gmail.com>
> ---
>  drivers/tty/serial/imx.c | 5 +++--
>  1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index be00362b8b67..f4236e8995fa 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -890,14 +890,15 @@ static irqreturn_t __imx_uart_rxint(int irq, void *dev_id)
>  	struct imx_port *sport = dev_id;
>  	unsigned int rx, flg;
>  	struct tty_port *port = &sport->port.state->port;
> +	typeof(sport->port.membase) membase = sport->port.membase;
>  	u32 usr2;
>  
>  	/* If we received something, check for 0xff flood */
> -	usr2 = imx_uart_readl(sport, USR2);
> +	usr2 = readl(membase + USR2);
>  	if (usr2 & USR2_RDR)
>  		imx_uart_check_flood(sport, usr2);
>  
> -	while ((rx = imx_uart_readl(sport, URXD0)) & URXD_CHARRDY) {
> +	while ((rx = readl(membase + URXD0)) & URXD_CHARRDY) {
>  		flg = TTY_NORMAL;
>  		sport->port.icount.rx++;

One of the motivations to introduce imx_uart_readl was to have a single
place to add a debug output to be able to inspect what the driver is
doing.

I wonder where your need for higher speed comes from and if the compiler
really generates more effective code with your change.

Please either drop the patch from your series or provide the differences
the compiler produces and a benchmark.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | https://www.pengutronix.de/ |
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