Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755134AbbGTNAb (ORCPT ); Mon, 20 Jul 2015 09:00:31 -0400 Received: from mail-qg0-f42.google.com ([209.85.192.42]:33272 "EHLO mail-qg0-f42.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752423AbbGTNA3 (ORCPT ); Mon, 20 Jul 2015 09:00:29 -0400 Message-ID: <55ACF0E5.6040107@hurleysoftware.com> Date: Mon, 20 Jul 2015 09:00:21 -0400 From: Peter Hurley User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0 MIME-Version: 1.0 To: Juergen Borleis CC: linux-kernel@vger.kernel.org, Stefan Wahren , Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel@pengutronix.de Subject: Re: [PATCH v3] serial: mxs-auart: keep the AUART unit in reset state when not in use References: <1437032458-8577-1-git-send-email-jbe@pengutronix.de> <55A8FEAE.9010502@hurleysoftware.com> <201507201004.02646.jbe@pengutronix.de> In-Reply-To: <201507201004.02646.jbe@pengutronix.de> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 4853 Lines: 136 On 07/20/2015 04:04 AM, Juergen Borleis wrote: > Hi Peter, > > On Friday 17 July 2015 15:10:06 Peter Hurley wrote: >> On 07/16/2015 03:40 AM, Juergen Borleis wrote: >>> 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 >>> --- >>> >>> Notes: >>> v3: >>> - missing newline added to an error message >>> >>> v2: >>> - rename mxs_auart_do_reset() to mxs_auart_keep_reset() to better >>> reflect what it really does >>> - adapt the delay in mxs_auart_keep_reset() to wait for the reset of >>> the AURAT unit to what is used in mxs_auart_reset() >> >> The function names and semantics are not clear. See below. >> >>> - typo fixed >>> >>> 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..135ee6c 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.\n"); >>> +} >>> + >>> static int mxs_auart_startup(struct uart_port *u) >>> { >>> int ret; >>> @@ -867,7 +891,10 @@ static int mxs_auart_startup(struct uart_port *u) >>> if (ret) >>> return ret; >>> >>> - writel(AUART_CTRL0_CLKGATE, u->membase + AUART_CTRL0_CLR); >>> + /* reset the unit if not aleady done */ >>> + mxs_auart_keep_reset(u); >> >> Why is this performing a soft-reset on open now? Didn't >> mxs_auart_shutdown() already leave it in this state? > > The probe function let the device left without reset. That is why I do a reset > here (which is skipped if the device is already in reset state). So you're "fixing" something else (reset @ probe) without _any_ indication in the changelog? >> Because if you're performing a soft-reset deliberately as part of the >> initial condition, you make no mention of that in the changelog. > > If I switch the device into the reset state immediately after the probe > function has finished, I could skip this additional reset. > >>> + /* bring it out of reset now */ >>> + mxs_auart_reset(u); >> >> mxs_auart_reset() is really not resetting but simply performing a block >> enable. Isn't there a generic block enable for the iMX.2x SoCs? (Maybe >> there should be) >> >> The names of these functions don't match expected operations of startup(). >> Start up should be enabling the device, not keeping it in reset. >> >> And "keep reset" immediately followed by "reset" makes no sense. > > mxs_auart_reset() is a bad name from the beginning. But I just wanted to keep > this change small and only change things that are really required. > I will try with a V4. ISTM this should be split into 2 or 3 separate patches: 1. Rename mxs_auart_reset() 2. Fix stale rx on re-open 3. Reset @ probe Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/