From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATCH v4 2/2] serial: mxs-auart: keep the AUART unit in reset state when not in use Date: Fri, 07 Aug 2015 11:30:27 -0400 Message-ID: <55C4CF13.90206@hurleysoftware.com> References: <1438944424-9053-1-git-send-email-jbe@pengutronix.de> <1438944424-9053-2-git-send-email-jbe@pengutronix.de> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1438944424-9053-2-git-send-email-jbe@pengutronix.de> Sender: linux-kernel-owner@vger.kernel.org To: Juergen Borleis , linux-kernel@vger.kernel.org Cc: Stefan Wahren , linux-serial@vger.kernel.org, Greg Kroah-Hartman , kernel@pengutronix.de, Jiri Slaby , linux-arm-kernel@lists.infradead.org List-Id: linux-serial@vger.kernel.org On 08/07/2015 06:47 AM, Juergen Borleis wrote: > Whenever the UART device driver gets closed from userland, the driver > disables the UART unit and then stops the clocks 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() when re-enabling the unit's clock. > > In this case we end up receiving an additional bogus character > immediately. > > The solution in this change is to switch the AUART unit into its reset > state on close() and only release it from its reset state on the next > open(). > > Note: when the unit is also used as system console it is always 'in use', > so we cannot reset it on close(). The code is still a bit ackward but looks functional, so Reviewed-by: Peter Hurley PS - This mxs driver has the same problem as the i.MX driver. The irq request and hardware init should be done in startup(). From mboxrd@z Thu Jan 1 00:00:00 1970 From: peter@hurleysoftware.com (Peter Hurley) Date: Fri, 07 Aug 2015 11:30:27 -0400 Subject: [PATCH v4 2/2] serial: mxs-auart: keep the AUART unit in reset state when not in use In-Reply-To: <1438944424-9053-2-git-send-email-jbe@pengutronix.de> References: <1438944424-9053-1-git-send-email-jbe@pengutronix.de> <1438944424-9053-2-git-send-email-jbe@pengutronix.de> Message-ID: <55C4CF13.90206@hurleysoftware.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 08/07/2015 06:47 AM, Juergen Borleis wrote: > Whenever the UART device driver gets closed from userland, the driver > disables the UART unit and then stops the clocks 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() when re-enabling the unit's clock. > > In this case we end up receiving an additional bogus character > immediately. > > The solution in this change is to switch the AUART unit into its reset > state on close() and only release it from its reset state on the next > open(). > > Note: when the unit is also used as system console it is always 'in use', > so we cannot reset it on close(). The code is still a bit ackward but looks functional, so Reviewed-by: Peter Hurley PS - This mxs driver has the same problem as the i.MX driver. The irq request and hardware init should be done in startup().