linux-kernel - Re: [PATCH v3 08/13] tty: serial: qcom-geni-serial: refactor qcom_geni_serial_handle

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Date:   Thu, 24 Nov 2022 15:51:13 +0100
From:   Bartosz Golaszewski <brgl@...ev.pl>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Srinivas Kandagatla <srinivas.kandagatla@...aro.org>,
        Vinod Koul <vkoul@...nel.org>, Alex Elder <elder@...nel.org>,
        Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-serial@...r.kernel.org,
        Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v3 08/13] tty: serial: qcom-geni-serial: refactor qcom_geni_serial_handle_tx()

On Thu, Nov 24, 2022 at 8:18 AM Jiri Slaby <jirislaby@...nel.org> wrote:
>
> On 23. 11. 22, 12:07, Bartosz Golaszewski wrote:
> > From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> >
> > qcom_geni_serial_handle_tx() is pretty big, let's move the code that
> > handles the actual writing of data to a separate function which makes
> > sense in preparation for introducing a dma variant of handle_tx().
> >
> > Let's also shuffle the code a bit, drop unneeded variables and use
> > uart_xmit_advance() instead of handling tail->xmit manually.
> >
> > Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
> > ---
> >   drivers/tty/serial/qcom_geni_serial.c | 54 +++++++++++++--------------
> >   1 file changed, 27 insertions(+), 27 deletions(-)
> >
> > diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> > index 68a1402fbe58..658b6d596f58 100644
> > --- a/drivers/tty/serial/qcom_geni_serial.c
> > +++ b/drivers/tty/serial/qcom_geni_serial.c
> > @@ -704,19 +704,42 @@ static void qcom_geni_serial_start_rx(struct uart_port *uport)
> >       writel(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
> >   }
>
> I know you just shuffle the code, but:
>
> > +static void qcom_geni_serial_send_chunk_fifo(struct uart_port *uport,
> > +                                          unsigned int chunk)
> > +{
> > +     struct qcom_geni_serial_port *port = to_dev_port(uport);
> > +     struct circ_buf *xmit = &uport->state->xmit;
> > +     u8 buf[BYTES_PER_FIFO_WORD];
> > +     size_t remaining = chunk;
>
> Why size_t when the others are uints? Well, BYTES_PER_FIFO_WORD should
> be defined as 4U.

Good point.

>
> > +     unsigned int tx_bytes;
> > +     int c;
> > +
> > +     while (remaining) {
> > +             memset(buf, 0, sizeof(buf));
> > +             tx_bytes = min_t(size_t, remaining, BYTES_PER_FIFO_WORD);
>
> Then, no need for min_t.
>

Same.

> > +
> > +             for (c = 0; c < tx_bytes ; c++) {
> > +                     buf[c] = xmit->buf[xmit->tail];
> > +                     uart_xmit_advance(uport, 1);
> > +             }
> > +
> > +             iowrite32_rep(uport->membase + SE_GENI_TX_FIFOn, buf, 1);
>
> I wonder, why is _rep variant used to transfer a single word? Only to
> hide the cast?
>

Even if - using writel() with a cast doesn't seem to improve the
performance and this one looks prettier IMO.

Bartosz