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

[Ilpo Järvinen]

On Wed, 18 Jan 2023, Sergey Organov wrote:

> Ilpo Järvinen <ilpo.jarvinen at linux.intel.com> writes:
> 
> > On Tue, 17 Jan 2023, Sergey Organov wrote:
> >
> >> Ilpo Järvinen <ilpo.jarvinen at linux.intel.com> writes:
> >> 
> >> > On Fri, 13 Jan 2023, 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++;
> >> >
> >> > I'd just make a uport local variable and use uport->membase + xx. There 
> >> > are plenty of sport->port constructs to replace with uport in that 
> >> > function anyway.
> >> 
> >> OK, thanks, will do it this way. Probably with global rename over this
> >> function in a separate patch?
> >
> > Yes, it is better to have it in own patch.
> 
> Well, it now seems that I'll drop this patch altogether, by agreement
> with Uwe. Do you think introducing of 'uport' still worth it in this
> one function? I figure it's probably not, provided the reset of the code
> in the driver still doesn't use the idiom.

I've no strong opinion either way. So feel free to leave them as they are 
now.

-- 
 i.