Re: [PATCH v2] serial: mxs-auart: keep the AUART unit in reset state when not in use
From: Stefan Wahren <hidden>
Date: 2015-07-15 16:07:40
Also in:
linux-arm-kernel, lkml
Hi Juergen, Am 15.07.2015 um 09:36 schrieb Juergen Borleis:
Whenever the UART device driver gets closed from userland, the driver disables the UART unit and then stops its clock to save power. The bit which disabled the UART unit is described as: "UART Enable. If this bit is set to 1, the UART is enabled. Data transmission and reception occurs for the UART signals. When the UART is disabled in the middle of transmission or reception, it completes the current character before stopping." The important part is the "it completes the current character". Whenever a reception is ongoing when the UART gets disabled (including the clock off) the statemachine freezes and "remembers" this state on the next open() and re-enabling of the unit's clock. In this case we end up receiving an additional bogus character immediately. The solution in this change is to move the AUART unit into its reset state on close() and only release it from its reset state on the next open(). Signed-off-by: Juergen Borleis <redacted> ---
changelog for v2?
quoted hunk ↗ jump to hunk
drivers/tty/serial/mxs-auart.c | 38 ++++++++++++++++++++++++++++++-------- 1 file changed, 30 insertions(+), 8 deletions(-)diff --git a/drivers/tty/serial/mxs-auart.c b/drivers/tty/serial/mxs-auart.c index 13cf773..13b3e3c 100644 --- a/drivers/tty/serial/mxs-auart.c +++ b/drivers/tty/serial/mxs-auart.c@@ -858,6 +858,30 @@ static void mxs_auart_reset(struct uart_port *u) writel(AUART_CTRL0_CLKGATE, u->membase + AUART_CTRL0_CLR); } +static void mxs_auart_keep_reset(struct uart_port *u) +{ + int i; + u32 reg; + + reg = readl(u->membase + AUART_CTRL0); + /* if already in reset state, keep it untouched */ + if (reg & AUART_CTRL0_SFTRST) + return; + + writel(AUART_CTRL0_CLKGATE, u->membase + AUART_CTRL0_CLR); + writel(AUART_CTRL0_SFTRST, u->membase + AUART_CTRL0_SET); + + for (i = 0; i < 10000; i++) { + reg = readl(u->membase + AUART_CTRL0); + /* reset is finished when the clock is gated */ + if (reg & AUART_CTRL0_CLKGATE) + return; + udelay(3); + } + + dev_err(u->dev, "Failed to reset the unit.");
Sorry, i missed that in my first review. It looks like that the newline at the end of the error message is missing. Regards Stefan