From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Hurley Subject: Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx Date: Fri, 20 Nov 2015 12:12:29 -0500 Message-ID: <564F547D.4070808@hurleysoftware.com> References: <1447963344-16266-1-git-send-email-soren.brinkmann@xilinx.com> <1447963344-16266-4-git-send-email-soren.brinkmann@xilinx.com> <564F0E75.5020100@hurleysoftware.com> <20151120170525.GW32017@xsjsorenbubuntu> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <20151120170525.GW32017@xsjsorenbubuntu> Sender: linux-kernel-owner@vger.kernel.org To: =?UTF-8?Q?S=c3=b6ren_Brinkmann?= Cc: Greg Kroah-Hartman , Jiri Slaby , linux-arm-kernel@lists.infradead.org, Michal Simek , linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-serial@vger.kernel.org On 11/20/2015 12:05 PM, S=C3=B6ren Brinkmann wrote: > On Fri, 2015-11-20 at 07:13AM -0500, Peter Hurley wrote: >> >> >> On 11/19/2015 03:02 PM, Soren Brinkmann wrote: >>> start_tx must start transmitting characters. Regardless of the stat= e of >>> the circular buffer, always enable the transmitter hardware. >> >> Why? >> >> Does cdns_uart_stop_tx() actually stop the transmitter so that >> data remains in the transmitter? >=20 > Fixing up the patch, I looked at this one. It might actually do that. Ok. > Without having changed anything. The doc says: "The driver should > stop transmitting characters as soon as possible.". And the > implementation is really not draining any FIFO, but just disabling th= e > transmitter. I take your question as that this might not be this way? > Should stop_tx drain the FIFO first? No. Most h/w can't actually stop the transmitter (or not without losing data), so that's why the expectation is only for "as soon as possible". Stopping sooner is better. Regards, Peter Hurley From mboxrd@z Thu Jan 1 00:00:00 1970 From: peter@hurleysoftware.com (Peter Hurley) Date: Fri, 20 Nov 2015 12:12:29 -0500 Subject: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx In-Reply-To: <20151120170525.GW32017@xsjsorenbubuntu> References: <1447963344-16266-1-git-send-email-soren.brinkmann@xilinx.com> <1447963344-16266-4-git-send-email-soren.brinkmann@xilinx.com> <564F0E75.5020100@hurleysoftware.com> <20151120170525.GW32017@xsjsorenbubuntu> Message-ID: <564F547D.4070808@hurleysoftware.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On 11/20/2015 12:05 PM, S?ren Brinkmann wrote: > On Fri, 2015-11-20 at 07:13AM -0500, Peter Hurley wrote: >> >> >> On 11/19/2015 03:02 PM, Soren Brinkmann wrote: >>> start_tx must start transmitting characters. Regardless of the state of >>> the circular buffer, always enable the transmitter hardware. >> >> Why? >> >> Does cdns_uart_stop_tx() actually stop the transmitter so that >> data remains in the transmitter? > > Fixing up the patch, I looked at this one. It might actually do that. Ok. > Without having changed anything. The doc says: "The driver should > stop transmitting characters as soon as possible.". And the > implementation is really not draining any FIFO, but just disabling the > transmitter. I take your question as that this might not be this way? > Should stop_tx drain the FIFO first? No. Most h/w can't actually stop the transmitter (or not without losing data), so that's why the expectation is only for "as soon as possible". Stopping sooner is better. Regards, Peter Hurley