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

From: "Ilpo Järvinen" <ilpo.jarvinen@linux.intel.com>
To: Sergey Organov <sorganov@gmail.com>
Cc: linux-serial <linux-serial@vger.kernel.org>,
	"Fabio Estevam" <festevam@gmail.com>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Jiri Slaby" <jirislaby@kernel.org>,
	"Richard Genoud" <richard.genoud@gmail.com>,
	"Sascha Hauer" <s.hauer@pengutronix.de>,
	"Shawn Guo" <shawnguo@kernel.org>,
	"Tim Harvey" <tharvey@gateworks.com>,
	"Tomasz Moń" <tomasz.mon@camlingroup.com>,
	linux-arm-kernel@lists.infradead.org,
	"NXP Linux Team" <linux-imx@nxp.com>,
	"Pengutronix Kernel Team" <kernel@pengutronix.de>
Subject: Re: [PATCH 7/8] serial: imx: use readl() to optimize FIFO reading loop
Date: Wed, 18 Jan 2023 21:29:49 +0200 (EET)	[thread overview]
Message-ID: <bc348d2-234e-3a30-272b-b17d27da7327@linux.intel.com> (raw)
In-Reply-To: <87edrrzw3n.fsf@osv.gnss.ru>

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On Wed, 18 Jan 2023, Sergey Organov wrote:

> Ilpo Järvinen <ilpo.jarvinen@linux.intel.com> writes:
> 
> > On Tue, 17 Jan 2023, Sergey Organov wrote:
> >
> >> Ilpo Järvinen <ilpo.jarvinen@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@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.

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