From mboxrd@z Thu Jan 1 00:00:00 1970 From: Murali Karicheri Subject: Re: [PATCH v2] serial: uart: add hw flow control support configuration Date: Thu, 7 Aug 2014 13:34:04 -0400 Message-ID: <53E3B88C.2000209@ti.com> References: <1398971093-17164-1-git-send-email-m-karicheri2@ti.com> <53E39B44.60406@hurleysoftware.com> <53E3A67B.6070709@ti.com> <20140807171254.GA13097@kroah.com> <53E3B67E.80705@hurleysoftware.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8"; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <53E3B67E.80705@hurleysoftware.com> Sender: linux-doc-owner@vger.kernel.org To: Peter Hurley Cc: Greg Kroah-Hartman , devicetree@vger.kernel.org, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-serial@vger.kernel.org, Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Randy Dunlap , Jiri Slaby , Santosh Shilimkar List-Id: devicetree@vger.kernel.org On 08/07/2014 01:25 PM, Peter Hurley wrote: > On 08/07/2014 01:12 PM, Greg Kroah-Hartman wrote: >> On Thu, Aug 07, 2014 at 12:16:59PM -0400, Murali Karicheri wrote: >>> On 08/07/2014 11:29 AM, Peter Hurley wrote: >>>> On 05/01/2014 03:04 PM, Murali Karicheri wrote: >>>>> 8250 uart driver currently supports only software assisted hw flow >>>>> control. The software assisted hw flow control maintains a hw_stopped >>>>> flag in the tty structure to stop and start transmission and use modem >>>>> status interrupt for the event to drive the handshake signals. This is >>>>> not needed if hw has flow control capabilities. This patch adds a >>>>> DT attribute for enabling hw flow control for a uart port. Also skip >>>>> stop and start if this flag is present in flag field of the port >>>>> structure. >>>>> >>>>> Signed-off-by: Murali Karicheri >>>>> >>>>> CC: Rob Herring >>>>> CC: Pawel Moll >>>>> CC: Mark Rutland >>>>> CC: Ian Campbell >>>>> CC: Kumar Gala >>>>> CC: Randy Dunlap >>>>> CC: Greg Kroah-Hartman >>>>> CC: Jiri Slaby >>>>> CC: Santosh Shilimkar >>>>> --- >>>>> .../devicetree/bindings/serial/of-serial.txt | 1 + >>>>> drivers/tty/serial/8250/8250_core.c | 6 ++++-- >>>>> drivers/tty/serial/of_serial.c | 4 ++++ >>>>> drivers/tty/serial/serial_core.c | 12 +++++++++--- >>>>> 4 files changed, 18 insertions(+), 5 deletions(-) >>>>> >>>> [...] >>>> >>>>> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c >>>>> index b68550d..851707a 100644 >>>>> --- a/drivers/tty/serial/serial_core.c >>>>> +++ b/drivers/tty/serial/serial_core.c >>>>> @@ -174,8 +174,12 @@ static int uart_port_startup(struct tty_struct *tty, struct uart_state *state, >>>>> if (tty->termios.c_cflag& CBAUD) >>>>> uart_set_mctrl(uport, TIOCM_RTS | TIOCM_DTR); >>>>> } >>>>> - >>>>> - if (tty_port_cts_enabled(port)) { >>>>> + /* >>>>> + * if hw support flow control without software intervention, >>>>> + * then skip the below check >>>>> + */ >>>>> + if (tty_port_cts_enabled(port)&& >>>>> + !(uport->flags& UPF_HARD_FLOW)) { >>>>> spin_lock_irq(&uport->lock); >>>>> if (!(uport->ops->get_mctrl(uport)& TIOCM_CTS)) >>>>> tty->hw_stopped = 1; >>>>> @@ -2772,7 +2776,9 @@ void uart_handle_cts_change(struct uart_port *uport, unsigned int status) >>>>> >>>>> uport->icount.cts++; >>>>> >>>>> - if (tty_port_cts_enabled(port)) { >>>>> + /* skip below code if the hw flow control is supported */ >>>>> + if (tty_port_cts_enabled(port)&& >>>>> + !(uport->flags& UPF_HARD_FLOW)) { >>>> Why is a modem status interrupt being generated for DCTS >>>> if autoflow control is enabled? >>>> >>>> This should be: >>>> >>>> WARN_ON_ONCE(uport->flags& UPF_HARD_FLOW); >>>> >>>> to indicate a mis-configured driver/device. >>> This patch is already merged to the upstream branch and if you see any >>> issue, please >>> post a patch for review. >> >> If someone points out a problem in a patch of yours that is accepted >> upstream, it is nice to provide a fix, otherwise I will just revert it >> upstream, as it looks to be incorrect. >> >> So, should I just revert it? > > Greg, > > As I look this patch over further, this should just be reverted. Sorry, I would suggest to fix it rather revert it. > > 1. The patch enables UPF_HARD_FLOW, but provides no throttle() and unthrottle() > methods for 8250, which is guaranteed to blow-up when either uart_throttle() or > uart_unthrottle() is called. > > 2. The patch adds capabilities which already exist, namely UART_CAP_AFE. AFAIK, UART_CAP_AFE is a software assisted hw flow control and it was described in my commit log as well where as this patch add support for pure h/w controlled flow control and no software intervention is needed. Do you think uart_throttle() or uart_unthrottle() is applicable in this case? Murali > > Regards, > Peter Hurley >