Hi,
On Wed, Dec 19, 2018 at 2:12 PM Evan Green <evgreen@xxxxxxxxxxxx> wrote:
>
> On Wed, Dec 19, 2018 at 12:34 PM Ryan Case <ryandcase@xxxxxxxxxxxx> wrote:
> >
> > If a serial console write occured while a UART transmit command was
> > waiting for a done signal then no further data would be sent until
> > something new kicked the system into gear. If there is already data
> > waiting in the circular buffer we must re-enable the tx watermark so we
> > receive the expected interrupts.
> >
> > Signed-off-by: Ryan Case <ryandcase@xxxxxxxxxxxx>
> > ---
> >
> > drivers/tty/serial/qcom_geni_serial.c | 8 ++++++++
> > 1 file changed, 8 insertions(+)
> >
> > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> > index 0c93beb69e73..a694a47747c7 100644
> > --- a/drivers/tty/serial/qcom_geni_serial.c
> > +++ b/drivers/tty/serial/qcom_geni_serial.c
> > @@ -442,6 +442,7 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> > bool locked = true;
> > unsigned long flags;
> > u32 geni_status;
> > + u32 irq_en;
> >
> > WARN_ON(co->index < 0 || co->index >= GENI_UART_CONS_PORTS);
> >
> > @@ -476,6 +477,13 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> > * has been sent, in which case we need to look for done first.
> > */
> > qcom_geni_serial_poll_tx_done(uport);
> > +
> > + if (uart_circ_chars_pending(&uport->state->xmit)) {
> > + irq_en = readl_relaxed(uport->membase +
> > + SE_GENI_M_IRQ_EN);
> > + writel_relaxed(irq_en | M_TX_FIFO_WATERMARK_EN,
> > + uport->membase + SE_GENI_M_IRQ_EN);
>
> The _relaxed part of it has always been weird to me, but I guess we
> fought that battle awhile ago with this driver and lost.
>
> I suppose the only real danger with relaxed would be if you could get
> yourself into some sort of tight loop or idle where the CPU's write
> queue never flushes, but you needed it to in order to proceed. This
> probably could never happen, especially with locks around consoles and
> uart ports that act as barriers.
Yeah. IMO we should go through and remove all the "_relaxed" from
this driver until someone can prove that it's important for
performance. ...but I think that's for a future patch to do.
-Doug
