From mboxrd@z Thu Jan 1 00:00:00 1970 From: Bjorn Andersson Subject: Re: [PATCH] tty: serial: msm_serial: Fix XON/XOFF Date: Mon, 20 May 2019 08:11:01 -0700 Message-ID: <20190520151101.GN2085@tuxbook-pro> References: <20190520103435.30850-1-jorge.ramirez-ortiz@linaro.org> <20190520145110.7BDAE21721@mail.kernel.org> <254704a2-ee20-30cd-8362-6e1bd23ec090@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Jorge Ramirez Cc: Stephen Boyd , agross@kernel.org, david.brown@linaro.org, gregkh@linuxfoundation.org, jslaby@suse.com, keescook@chromium.org, anton@enomsg.org, ccross@android.com, tony.luck@intel.com, linux-arm-msm@vger.kernel.org, linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org, khasim.mohammed@linaro.org, agsumit@qti.qualcomm.com List-Id: linux-serial@vger.kernel.org On Mon 20 May 07:58 PDT 2019, Jorge Ramirez wrote: > On 5/20/19 16:56, Jorge Ramirez wrote: > > On 5/20/19 16:51, Stephen Boyd wrote: > >> Quoting Jorge Ramirez-Ortiz (2019-05-20 03:34:35) > >>> When the tty layer requests the uart to throttle, the current code > >>> executing in msm_serial will trigger "Bad mode in Error Handler" and > >>> generate an invalid stack frame in pstore before rebooting (that is if > >>> pstore is indeed configured: otherwise the user shall just notice a > >>> reboot with no further information dumped to the console). > >>> > >>> This patch replaces the PIO byte accessor with the word accessor > >>> already used in PIO mode. > >> > >> Because the hardware only accepts word based accessors and fails > >> otherwise? I can believe that. > >> > >> I wonder if the earlier UART hardware this driver used to support (i.e. > >> pre-DM) would accept byte access to the registers. It's possible, but we > >> don't really care because those boards aren't supported. > > > > ok. > > > > also the PIO path uses iowrite32_rep to write a number of bytes (from 1 > > to 4) so I think it is also appropriate to use it for XON/XOFF. > > > >> > >>> > >>> Signed-off-by: Jorge Ramirez-Ortiz > >>> --- > >> > >> Reviewed-by: Stephen Boyd > >> > >>> drivers/tty/serial/msm_serial.c | 5 ++++- > >>> 1 file changed, 4 insertions(+), 1 deletion(-) > >>> > >>> diff --git a/drivers/tty/serial/msm_serial.c b/drivers/tty/serial/msm_serial.c > >>> index 109096033bb1..23833ad952ba 100644 > >>> --- a/drivers/tty/serial/msm_serial.c > >>> +++ b/drivers/tty/serial/msm_serial.c > >>> @@ -869,10 +870,12 @@ static void msm_handle_tx(struct uart_port *port) > >>> else > >>> tf = port->membase + UART_TF; > >>> > >>> + buf[0] = port->x_char; > >>> + > >>> if (msm_port->is_uartdm) > >>> msm_reset_dm_count(port, 1); > >>> > >>> - iowrite8_rep(tf, &port->x_char, 1); > >>> + iowrite32_rep(tf, buf, 1); > >> > >> I suppose it's OK to write some extra zeroes here? > >> > >> > > > > yeah, semantically confusing msm_reset_dm_count is what really matters: > > it tells the hardware to only take n bytes (in this case only one) so > > the others will be ignored > > um after I said this, maybe iowrite32_rep should only be applied to > uartdm ... what do you think? > If I read the history correctly this write was a writel() up until 68252424a7c7 ("tty: serial: msm: Support big-endian CPUs"). So I think you should just change this back to a iowrite32_rep() and add a Fixes tag. Regards, Bjorn