Quoting Ryan Case (2018-11-27 17:24:44)
> On Tue, Nov 27, 2018 at 4:20 PM Stephen Boyd <swboyd@xxxxxxxxxxxx> wrote:
> >
> > Quoting Ryan Case (2018-11-26 18:25:36)
> > > Transfers were being divided into device FIFO sized (64 byte max)
> > > operations which would poll for completion within a spin_lock_irqsave /
> > > spin_unlock_irqrestore block. This both made things slow by waiting for
> > > the FIFO to completely drain before adding further data and would also
> > > result in softlocks on large transmissions.
> > >
> > > This patch allows larger transfers with continuous FIFO additions as
> > > space becomes available and removes polling from the interrupt handler.
> > >
> > > Signed-off-by: Ryan Case <ryandcase@xxxxxxxxxxxx>
> > > Version: 1
> >
> > I've never seen a Version tag before. Did you manually add this?
>
> I submitted with patman, this should have been Series-version:
Hmm ok. I'm not aware of this being a kernel idiom so I would remove
this tag before sending.
>
> >
> > >
> > > WARN_ON(co->index < 0 || co->index >= GENI_UART_CONS_PORTS);
> > >
> > > @@ -465,9 +470,17 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> > > }
> > > writel_relaxed(M_CMD_CANCEL_EN, uport->membase +
> > > SE_GENI_M_IRQ_CLEAR);
> > > - }
> > > + } else if ((geni_status & M_GENI_CMD_ACTIVE) && !port->cur_tx_remaining)
> > > + /* It seems we can interrupt existing transfers unless all data
> >
> > Nitpick: Have /* on a line by itself
> >
> > Is this comment supposed to say "we can't interrupt existing transfers"?
>
> Nope, comment is correct as is.
Ok. I fail at parsing it then. Perhaps
"It seems we can interrupt existing transfers except for when all data
has been sent"
would make it easier for me to read.
>
> >
> > >
> > > __qcom_geni_serial_console_write(uport, s, count);
> > > +
> > > + if (port->cur_tx_remaining)
> > > + qcom_geni_serial_setup_tx(uport, port->cur_tx_remaining);
> >
> > Does this happen? Is the console being used as a tty at the same time?
>
> Yup, happens quite a bit.
So its being used in both modes at the same time?
>
> >
> > > +
> > > if (locked)
> > > spin_unlock_irqrestore(&uport->lock, flags);
> > > }
> > > @@ -701,40 +714,47 @@ static void qcom_geni_serial_handle_rx(struct uart_port *uport, bool drop)
> > > port->handle_rx(uport, total_bytes, drop);
> > > }
> > >
> > > -static void qcom_geni_serial_handle_tx(struct uart_port *uport)
> > > +static void qcom_geni_serial_handle_tx(struct uart_port *uport, bool done,
> > > + bool active)
> > > {
> > > struct qcom_geni_serial_port *port = to_dev_port(uport, uport);
> > > struct circ_buf *xmit = &uport->state->xmit;
> > > size_t avail;
> > > size_t remaining;
> > > + size_t pending;
> > > int i;
> > > u32 status;
> > > unsigned int chunk;
> > > int tail;
> > > - u32 irq_en;
> > >
> > > - chunk = uart_circ_chars_pending(xmit);
> > > status = readl_relaxed(uport->membase + SE_GENI_TX_FIFO_STATUS);
> > > - /* Both FIFO and framework buffer are drained */
> > > - if (!chunk && !status) {
> > > +
> > > + /* Complete the current tx command before taking newly added data */
> > > + if (active)
> > > + pending = port->cur_tx_remaining;
> > > + else
> > > + pending = uart_circ_chars_pending(xmit);
> > > +
> > > + /* All data has been transmitted and acknowledged as received */
> > > + if (!pending && !status && done) {
> >
> > Nitpick: status is a poor variable name to test here. I don't understand
> > what this line is doing. Maybe it would help to have another local
> > variable like 'needs_attention'?
>
> It could be renamed but since this isn't a general file cleanup patch
> I was avoiding non-functional changes. It is the TX_FIFO_STATUS
> register, if non-zero there is still data in the FIFO or related
> activity ongoing.
Ok.
>
> >
> > > qcom_geni_serial_stop_tx(uport);
> > > goto out_write_wakeup;
> > > }
> > >
> > > - if (!uart_console(uport)) {
> > > - irq_en = readl_relaxed(uport->membase + SE_GENI_M_IRQ_EN);
> > > - irq_en &= ~(M_TX_FIFO_WATERMARK_EN);
> > > - writel_relaxed(0, uport->membase + SE_GENI_TX_WATERMARK_REG);
> > > - writel_relaxed(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
> > > - }
> > > + avail = port->tx_fifo_depth - (status & TX_FIFO_WC);
> > > + avail *= port->tx_bytes_pw;
> > > + if (avail < 0)
> > > + avail = 0;
> >
> > How can 'avail' be less than 0? It's size_t which is unsigned? If
> > underflow is happening from that subtraction or overflow from the
> > multiply that could be bad but I hope that is impossible.
>
> I hope underflow is impossible as well. However, if the hardware did
> wind up in a strange state I wanted to err on the side of not throwing
> away data and being able to resume later if things recovered. I can
> remove the defensive checks if that's the custom, otherwise I'll
> update the comparison logic accordingly.
Well it looks like impossible code because an unsigned value can't be
less than zero. So it's not about customs, more about dead code removal.
>
> >
> > >
> > > - avail = (port->tx_fifo_depth - port->tx_wm) * port->tx_bytes_pw;
> > > tail = xmit->tail;
> > > - chunk = min3((size_t)chunk, (size_t)(UART_XMIT_SIZE - tail), avail);
> > > + chunk = min3((size_t)pending, (size_t)(UART_XMIT_SIZE - tail), avail);
> >
> > Nitpick: If we made 'avail' unsigned int would we be able to drop the
> > casts on this min3() call? This line is quite hard to read.
>
> Seems they can go away without any changes.
Ok!
