From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Simek Subject: Re: [PATH RESEND v2 03/10] tty: xuartps: Always enable transmitter in start_tx Date: Mon, 23 Nov 2015 08:05:54 +0100 Message-ID: <5652BAD2.4090000@xilinx.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> <20151120152849.GU32017@xsjsorenbubuntu> <564F4A95.3010303@hurleysoftware.com> <20151120165804.GV32017@xsjsorenbubuntu> <564F5574.4070407@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: In-Reply-To: <564F5574.4070407@hurleysoftware.com> Sender: linux-kernel-owner@vger.kernel.org To: Peter Hurley , =?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 Hi Peter, On 20.11.2015 18:16, Peter Hurley wrote: > On 11/20/2015 11:58 AM, S=C3=B6ren Brinkmann wrote: >> On Fri, 2015-11-20 at 11:30AM -0500, Peter Hurley wrote: >>> On 11/20/2015 10:28 AM, 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 s= tate 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? >>>> >>>> Well, I saw my system freezing and the cause seemed to be that the= UART >>>> receiver and/or transmitters were disabled while the system was tr= ying >>>> to print. Hence, I started questioning all locations touching the >>>> transmitter/receiver enable. I read the docs in >>>> https://www.kernel.org/doc/Documentation/serial/driver, which simp= ly >>>> says "Start transmitting characters." for start_tx(). Hence, I tho= ught, >>>> this function is probably supposed to just do that and start the >>>> transmitter. I'll test whether this patch can be dropped. >>> >>> I don't think that patch would fix any freeze problems, but restart= ing >>> the transmitter even if the circ buffer is empty may be necessary t= o >>> push out remaining data when the port is restarted after being stop= ped. >>> >>> IOW, something like >>> >>> if (uart_tx_stopped(port)) >>> return; >>> >>> .... >>> >>> >>> if (uart_circ_empty(&port->state->xmit) >>> return; >> >> Thanks! I'll change the patch accordingly. >> >>> >>> >>> Below is a (work-in-progress) serial driver validation test for flo= w >>> control handling (it may need some tuning for slow line speeds). >>> Usual caveats apply. Takes ~40secs @ 115200. >> >> I'll try to get that running on my system. >=20 > The test below should pass too, but I know it won't because this xili= nx > driver isn't handling x_char at all. >=20 > Aside: does this h/w have rts driver/cts receiver? >=20 > --- >% --- > --- /dev/null 2015-11-20 07:19:13.265468435 -0500 > +++ xchar.c 2015-11-20 11:55:26.210233102 -0500 > @@ -0,0 +1,354 @@ > +/* > + * x_char unit test for tty drivers All these tests looks very interesting. Do you have any any work-in-progress repo with other tests? It will be good to run all of them to validate our drivers. Thanks, Michal