From mboxrd@z Thu Jan 1 00:00:00 1970 From: Stefan Wahren Subject: Re: [PATCH v3] serial: mxs-auart: keep the AUART unit in reset state when not in use Date: Thu, 16 Jul 2015 17:36:17 +0200 Message-ID: <55A7CF71.7050507@i2se.com> References: <1437032458-8577-1-git-send-email-jbe@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1437032458-8577-1-git-send-email-jbe@pengutronix.de> Sender: linux-kernel-owner@vger.kernel.org To: Juergen Borleis , linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , Jiri Slaby , linux-serial@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kernel@pengutronix.de List-Id: linux-serial@vger.kernel.org > 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 > --- Acked-by: Stefan Wahren Thanks Stefan From mboxrd@z Thu Jan 1 00:00:00 1970 From: stefan.wahren@i2se.com (Stefan Wahren) Date: Thu, 16 Jul 2015 17:36:17 +0200 Subject: [PATCH v3] serial: mxs-auart: keep the AUART unit in reset state when not in use In-Reply-To: <1437032458-8577-1-git-send-email-jbe@pengutronix.de> References: <1437032458-8577-1-git-send-email-jbe@pengutronix.de> Message-ID: <55A7CF71.7050507@i2se.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org > 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 > --- Acked-by: Stefan Wahren Thanks Stefan