| Message ID | 20230109145925.1479749-1-loic.poulain@linaro.org |
|---|---|
| State | Superseded |
| Headers | show |
| Series | serial: mxc: Speed-up character transmission | expand |
Hi, On Mon, 9 Jan 2023 15:59:25 +0100 Loic Poulain wrote: > Instead of waiting for empty FIFO condition before writing a > character, wait for non-full FIFO condition. > > This helps in saving several tens of milliseconds during boot > (depending verbosity). > > Signed-off-by: Loic Poulain <loic.poulain@linaro.org> > --- > drivers/serial/serial_mxc.c | 8 ++++---- > 1 file changed, 4 insertions(+), 4 deletions(-) > > diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c > index 82c0d84628..f8c49865be 100644 > --- a/drivers/serial/serial_mxc.c > +++ b/drivers/serial/serial_mxc.c > @@ -223,11 +223,11 @@ static void mxc_serial_putc(const char c) > if (c == '\n') > serial_putc('\r'); > > - writel(c, &mxc_base->txd); > - > /* wait for transmitter to be ready */ > - while (!(readl(&mxc_base->ts) & UTS_TXEMPTY)) > + while (readl(&mxc_base->ts) & UTS_TXFULL) > schedule(); > + > + writel(c, &mxc_base->txd); > } > > /* Test whether a character is in the RX buffer */ > @@ -311,7 +311,7 @@ static int mxc_serial_putc(struct udevice *dev, const char ch) > struct mxc_serial_plat *plat = dev_get_plat(dev); > struct mxc_uart *const uart = plat->reg; > > - if (!(readl(&uart->ts) & UTS_TXEMPTY)) > + if (readl(&uart->ts) & UTS_TXFULL) > return -EAGAIN; > > writel(ch, &uart->txd); > A previous attempt to do this in: |commit c7878a0483c59c48a730123bc0f4659fd40921bf |Author: Johannes Schneider <johannes.schneider@leica-geosystems.com> |Date: Tue Sep 6 14:15:04 2022 +0200 | | serial: mxc: have putc use the TXFIFO has been reverted in: |commit fc1c1760de38823edbdc2cdd9606dff938a07f6e |Author: Fabio Estevam <festevam@denx.de> |Date: Tue Nov 8 08:39:33 2022 -0300 | | Revert "serial: mxc: have putc use the TXFIFO" | | This reverts commit c7878a0483c59c48a730123bc0f4659fd40921bf. | | Since commit c7878a0483c5 ("serial: mxc: have putc use the TXFIFO"), | serial console corruption can be seen when priting inside board_init(). | | Revert it to avoid the regression. | | Reported-by: Tim Harvey <tharvey@gateworks.com> | Signed-off-by: Fabio Estevam <festevam@denx.de> | Acked-by: Tim Harvey <tharvey@gateworks.com> Lothar Waßmann
Hi Lothar, On Tue, 10 Jan 2023 at 07:46, Lothar Waßmann <LW@karo-electronics.de> wrote: > A previous attempt to do this in: > |commit c7878a0483c59c48a730123bc0f4659fd40921bf > |Author: Johannes Schneider <johannes.schneider@leica-geosystems.com> > |Date: Tue Sep 6 14:15:04 2022 +0200 > | > | serial: mxc: have putc use the TXFIFO > > has been reverted in: > |commit fc1c1760de38823edbdc2cdd9606dff938a07f6e > |Author: Fabio Estevam <festevam@denx.de> > |Date: Tue Nov 8 08:39:33 2022 -0300 > | > | Revert "serial: mxc: have putc use the TXFIFO" > | > | This reverts commit c7878a0483c59c48a730123bc0f4659fd40921bf. > | > | Since commit c7878a0483c5 ("serial: mxc: have putc use the TXFIFO"), > | serial console corruption can be seen when priting inside board_init(). Thanks for highlighting this. Looked at it and reproduced some sort of corruption in board_init() as well, which seems due to reinitialization of the UART while TX is not complete. I'm going to follow up with a V2, including a fix for this. Regards, Loic
diff --git a/drivers/serial/serial_mxc.c b/drivers/serial/serial_mxc.c index 82c0d84628..f8c49865be 100644 --- a/drivers/serial/serial_mxc.c +++ b/drivers/serial/serial_mxc.c @@ -223,11 +223,11 @@ static void mxc_serial_putc(const char c) if (c == '\n') serial_putc('\r'); - writel(c, &mxc_base->txd); - /* wait for transmitter to be ready */ - while (!(readl(&mxc_base->ts) & UTS_TXEMPTY)) + while (readl(&mxc_base->ts) & UTS_TXFULL) schedule(); + + writel(c, &mxc_base->txd); } /* Test whether a character is in the RX buffer */ @@ -311,7 +311,7 @@ static int mxc_serial_putc(struct udevice *dev, const char ch) struct mxc_serial_plat *plat = dev_get_plat(dev); struct mxc_uart *const uart = plat->reg; - if (!(readl(&uart->ts) & UTS_TXEMPTY)) + if (readl(&uart->ts) & UTS_TXFULL) return -EAGAIN; writel(ch, &uart->txd);
Instead of waiting for empty FIFO condition before writing a character, wait for non-full FIFO condition. This helps in saving several tens of milliseconds during boot (depending verbosity). Signed-off-by: Loic Poulain <loic.poulain@linaro.org> --- drivers/serial/serial_mxc.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-)