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<m-karicheri2@xxxxxx>
>>>>
>>>> CC: Rob Herring<robh+dt@xxxxxxxxxx>
>>>> CC: Pawel Moll<pawel.moll@xxxxxxx>
>>>> CC: Mark Rutland<mark.rutland@xxxxxxx>
>>>> CC: Ian Campbell<ijc+devicetree@xxxxxxxxxxxxxx>
>>>> CC: Kumar Gala<galak@xxxxxxxxxxxxxx>
>>>> CC: Randy Dunlap<rdunlap@xxxxxxxxxxxxx>
>>>> CC: Greg Kroah-Hartman<gregkh@xxxxxxxxxxxxxxxxxxx>
>>>> CC: Jiri Slaby<jslaby@xxxxxxx>
>>>> CC: Santosh Shilimkar<santosh.shilimkar@xxxxxx>
>>>> ---
>>>> .../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.
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.
Regards,
Peter Hurley
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