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Message-ID: <CAE=gft4HEZtSDE4dP6Pr3WEoNHi2WS6PaZCDkSp9rAvAkox9Hw@mail.gmail.com>
Date: Fri, 4 Jan 2019 11:03:05 -0800
From: Evan Green <evgreen@...omium.org>
To: Ryan Case <ryandcase@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Jiri Slaby <jslaby@...e.com>,
Doug Anderson <dianders@...omium.org>,
linux-kernel@...r.kernel.org, linux-serial@...r.kernel.org,
Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH 1/4] tty: serial: qcom_geni_serial: Remove use of
*_relaxed() and mb()
On Wed, Jan 2, 2019 at 1:37 PM Ryan Case <ryandcase@...omium.org> wrote:
>
> A frequent side comment has been to remove the use of writel_relaxed,
> readl_relaxed, and mb.
To provide a bit more motivation, you could add something to the
effect of "using the _relaxed variant introduces a significant amount
of complexity when reasoning about the code, and has not been shown to
provide a noticeable performance benefit in the case of this driver",
or something to that effect.
>
> Signed-off-by: Ryan Case <ryandcase@...omium.org>
> ---
>
> drivers/tty/serial/qcom_geni_serial.c | 187 +++++++++++---------------
> 1 file changed, 80 insertions(+), 107 deletions(-)
>
> diff --git a/drivers/tty/serial/qcom_geni_serial.c b/drivers/tty/serial/qcom_geni_serial.c
> index 2b1e73193dad..dc95b96148ed 100644
> --- a/drivers/tty/serial/qcom_geni_serial.c
> +++ b/drivers/tty/serial/qcom_geni_serial.c
> @@ -230,7 +230,7 @@ static unsigned int qcom_geni_serial_get_mctrl(struct uart_port *uport)
> if (uart_console(uport) || !uart_cts_enabled(uport)) {
> mctrl |= TIOCM_CTS;
> } else {
> - geni_ios = readl_relaxed(uport->membase + SE_GENI_IOS);
> + geni_ios = readl(uport->membase + SE_GENI_IOS);
> if (!(geni_ios & IO2_DATA_IN))
> mctrl |= TIOCM_CTS;
> }
> @@ -248,7 +248,7 @@ static void qcom_geni_serial_set_mctrl(struct uart_port *uport,
>
> if (!(mctrl & TIOCM_RTS))
> uart_manual_rfr = UART_MANUAL_RFR_EN | UART_RFR_NOT_READY;
> - writel_relaxed(uart_manual_rfr, uport->membase + SE_UART_MANUAL_RFR);
> + writel(uart_manual_rfr, uport->membase + SE_UART_MANUAL_RFR);
> }
>
> static const char *qcom_geni_serial_get_type(struct uart_port *uport)
> @@ -277,9 +277,6 @@ static bool qcom_geni_serial_poll_bit(struct uart_port *uport,
> unsigned int fifo_bits;
> unsigned long timeout_us = 20000;
>
> - /* Ensure polling is not re-ordered before the prior writes/reads */
> - mb();
> -
> if (uport->private_data) {
> port = to_dev_port(uport, uport);
> baud = port->baud;
> @@ -299,7 +296,7 @@ static bool qcom_geni_serial_poll_bit(struct uart_port *uport,
> */
> timeout_us = DIV_ROUND_UP(timeout_us, 10) * 10;
> while (timeout_us) {
> - reg = readl_relaxed(uport->membase + offset);
> + reg = readl(uport->membase + offset);
> if ((bool)(reg & field) == set)
> return true;
> udelay(10);
> @@ -312,7 +309,7 @@ static void qcom_geni_serial_setup_tx(struct uart_port *uport, u32 xmit_size)
> {
> u32 m_cmd;
>
> - writel_relaxed(xmit_size, uport->membase + SE_UART_TX_TRANS_LEN);
> + writel(xmit_size, uport->membase + SE_UART_TX_TRANS_LEN);
> m_cmd = UART_START_TX << M_OPCODE_SHFT;
> writel(m_cmd, uport->membase + SE_GENI_M_CMD0);
> }
> @@ -325,13 +322,13 @@ static void qcom_geni_serial_poll_tx_done(struct uart_port *uport)
> done = qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
> M_CMD_DONE_EN, true);
> if (!done) {
> - writel_relaxed(M_GENI_CMD_ABORT, uport->membase +
> + writel(M_GENI_CMD_ABORT, uport->membase +
> SE_GENI_M_CMD_CTRL_REG);
> irq_clear |= M_CMD_ABORT_EN;
> qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
> M_CMD_ABORT_EN, true);
> }
> - writel_relaxed(irq_clear, uport->membase + SE_GENI_M_IRQ_CLEAR);
> + writel(irq_clear, uport->membase + SE_GENI_M_IRQ_CLEAR);
> }
>
> static void qcom_geni_serial_abort_rx(struct uart_port *uport)
> @@ -341,8 +338,8 @@ static void qcom_geni_serial_abort_rx(struct uart_port *uport)
> writel(S_GENI_CMD_ABORT, uport->membase + SE_GENI_S_CMD_CTRL_REG);
> qcom_geni_serial_poll_bit(uport, SE_GENI_S_CMD_CTRL_REG,
> S_GENI_CMD_ABORT, false);
> - writel_relaxed(irq_clear, uport->membase + SE_GENI_S_IRQ_CLEAR);
> - writel_relaxed(FORCE_DEFAULT, uport->membase + GENI_FORCE_DEFAULT_REG);
> + writel(irq_clear, uport->membase + SE_GENI_S_IRQ_CLEAR);
> + writel(FORCE_DEFAULT, uport->membase + GENI_FORCE_DEFAULT_REG);
> }
>
> #ifdef CONFIG_CONSOLE_POLL
> @@ -351,19 +348,13 @@ static int qcom_geni_serial_get_char(struct uart_port *uport)
> u32 rx_fifo;
> u32 status;
>
> - status = readl_relaxed(uport->membase + SE_GENI_M_IRQ_STATUS);
> - writel_relaxed(status, uport->membase + SE_GENI_M_IRQ_CLEAR);
> -
> - status = readl_relaxed(uport->membase + SE_GENI_S_IRQ_STATUS);
> - writel_relaxed(status, uport->membase + SE_GENI_S_IRQ_CLEAR);
> + status = readl(uport->membase + SE_GENI_M_IRQ_STATUS);
> + writel(status, uport->membase + SE_GENI_M_IRQ_CLEAR);
>
> - /*
> - * Ensure the writes to clear interrupts is not re-ordered after
> - * reading the data.
> - */
> - mb();
> + status = readl(uport->membase + SE_GENI_S_IRQ_STATUS);
> + writel(status, uport->membase + SE_GENI_S_IRQ_CLEAR);
>
> - status = readl_relaxed(uport->membase + SE_GENI_RX_FIFO_STATUS);
> + status = readl(uport->membase + SE_GENI_RX_FIFO_STATUS);
> if (!(status & RX_FIFO_WC_MSK))
> return NO_POLL_CHAR;
>
> @@ -376,12 +367,12 @@ static void qcom_geni_serial_poll_put_char(struct uart_port *uport,
> {
> struct qcom_geni_serial_port *port = to_dev_port(uport, uport);
>
> - writel_relaxed(port->tx_wm, uport->membase + SE_GENI_TX_WATERMARK_REG);
> + writel(port->tx_wm, uport->membase + SE_GENI_TX_WATERMARK_REG);
> qcom_geni_serial_setup_tx(uport, 1);
> WARN_ON(!qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
> M_TX_FIFO_WATERMARK_EN, true));
> - writel_relaxed(c, uport->membase + SE_GENI_TX_FIFOn);
> - writel_relaxed(M_TX_FIFO_WATERMARK_EN, uport->membase +
> + writel(c, uport->membase + SE_GENI_TX_FIFOn);
> + writel(M_TX_FIFO_WATERMARK_EN, uport->membase +
> SE_GENI_M_IRQ_CLEAR);
I think this could fit on one line now.
> qcom_geni_serial_poll_tx_done(uport);
> }
> @@ -390,7 +381,7 @@ static void qcom_geni_serial_poll_put_char(struct uart_port *uport,
> #ifdef CONFIG_SERIAL_QCOM_GENI_CONSOLE
> static void qcom_geni_serial_wr_char(struct uart_port *uport, int ch)
> {
> - writel_relaxed(ch, uport->membase + SE_GENI_TX_FIFOn);
> + writel(ch, uport->membase + SE_GENI_TX_FIFOn);
> }
>
> static void
> @@ -409,7 +400,7 @@ __qcom_geni_serial_console_write(struct uart_port *uport, const char *s,
> bytes_to_send++;
> }
>
> - writel_relaxed(DEF_TX_WM, uport->membase + SE_GENI_TX_WATERMARK_REG);
> + writel(DEF_TX_WM, uport->membase + SE_GENI_TX_WATERMARK_REG);
> qcom_geni_serial_setup_tx(uport, bytes_to_send);
> for (i = 0; i < count; ) {
> size_t chars_to_write = 0;
> @@ -427,7 +418,7 @@ __qcom_geni_serial_console_write(struct uart_port *uport, const char *s,
> chars_to_write = min_t(size_t, count - i, avail / 2);
> uart_console_write(uport, s + i, chars_to_write,
> qcom_geni_serial_wr_char);
> - writel_relaxed(M_TX_FIFO_WATERMARK_EN, uport->membase +
> + writel(M_TX_FIFO_WATERMARK_EN, uport->membase +
> SE_GENI_M_IRQ_CLEAR);
> i += chars_to_write;
> }
> @@ -456,7 +447,7 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> else
> spin_lock_irqsave(&uport->lock, flags);
>
> - geni_status = readl_relaxed(uport->membase + SE_GENI_STATUS);
> + geni_status = readl(uport->membase + SE_GENI_STATUS);
>
> /* Cancel the current write to log the fault */
> if (!locked) {
> @@ -466,10 +457,10 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> geni_se_abort_m_cmd(&port->se);
> qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
> M_CMD_ABORT_EN, true);
> - writel_relaxed(M_CMD_ABORT_EN, uport->membase +
> + writel(M_CMD_ABORT_EN, uport->membase +
> SE_GENI_M_IRQ_CLEAR);
> }
> - writel_relaxed(M_CMD_CANCEL_EN, uport->membase +
> + writel(M_CMD_CANCEL_EN, uport->membase +
> SE_GENI_M_IRQ_CLEAR);
This one would also fit on one line now.
> } else if ((geni_status & M_GENI_CMD_ACTIVE) && !port->tx_remaining) {
> /*
> @@ -479,9 +470,9 @@ static void qcom_geni_serial_console_write(struct console *co, const char *s,
> qcom_geni_serial_poll_tx_done(uport);
>
> if (uart_circ_chars_pending(&uport->state->xmit)) {
> - irq_en = readl_relaxed(uport->membase +
> + irq_en = readl(uport->membase +
> SE_GENI_M_IRQ_EN);
This one too.
> - writel_relaxed(irq_en | M_TX_FIFO_WATERMARK_EN,
> + writel(irq_en | M_TX_FIFO_WATERMARK_EN,
> uport->membase + SE_GENI_M_IRQ_EN);
> }
> }
> @@ -585,12 +576,12 @@ static void qcom_geni_serial_start_tx(struct uart_port *uport)
> if (!qcom_geni_serial_tx_empty(uport))
> return;
>
> - irq_en = readl_relaxed(uport->membase + SE_GENI_M_IRQ_EN);
> + irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
> irq_en |= M_TX_FIFO_WATERMARK_EN | M_CMD_DONE_EN;
>
> - writel_relaxed(port->tx_wm, uport->membase +
> + writel(port->tx_wm, uport->membase +
> SE_GENI_TX_WATERMARK_REG);
This one too, though it looks like you fix that up in a later commit.
> - writel_relaxed(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
> + writel(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
> }
> }
>
> @@ -600,35 +591,29 @@ static void qcom_geni_serial_stop_tx(struct uart_port *uport)
> u32 status;
> struct qcom_geni_serial_port *port = to_dev_port(uport, uport);
>
> - irq_en = readl_relaxed(uport->membase + SE_GENI_M_IRQ_EN);
> + irq_en = readl(uport->membase + SE_GENI_M_IRQ_EN);
> irq_en &= ~M_CMD_DONE_EN;
> if (port->xfer_mode == GENI_SE_FIFO) {
> irq_en &= ~M_TX_FIFO_WATERMARK_EN;
> - writel_relaxed(0, uport->membase +
> + writel(0, uport->membase +
> SE_GENI_TX_WATERMARK_REG);
Here too, though it also appears fixed up by a later commit.
> }
> - writel_relaxed(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
> - status = readl_relaxed(uport->membase + SE_GENI_STATUS);
> + writel(irq_en, uport->membase + SE_GENI_M_IRQ_EN);
> + status = readl(uport->membase + SE_GENI_STATUS);
> /* Possible stop tx is called multiple times. */
> if (!(status & M_GENI_CMD_ACTIVE))
> return;
>
> - /*
> - * Ensure cancel command write is not re-ordered before checking
> - * the status of the Primary Sequencer.
> - */
> - mb();
> -
> geni_se_cancel_m_cmd(&port->se);
> if (!qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
> M_CMD_CANCEL_EN, true)) {
> geni_se_abort_m_cmd(&port->se);
> qcom_geni_serial_poll_bit(uport, SE_GENI_M_IRQ_STATUS,
> M_CMD_ABORT_EN, true);
> - writel_relaxed(M_CMD_ABORT_EN, uport->membase +
> + writel(M_CMD_ABORT_EN, uport->membase +
> SE_GENI_M_IRQ_CLEAR);
Here too.
> }
> - writel_relaxed(M_CMD_CANCEL_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
> + writel(M_CMD_CANCEL_EN, uport->membase + SE_GENI_M_IRQ_CLEAR);
> }
>
> static void qcom_geni_serial_start_rx(struct uart_port *uport)
> @@ -637,26 +622,20 @@ static void qcom_geni_serial_start_rx(struct uart_port *uport)
> u32 status;
> struct qcom_geni_serial_port *port = to_dev_port(uport, uport);
>
> - status = readl_relaxed(uport->membase + SE_GENI_STATUS);
> + status = readl(uport->membase + SE_GENI_STATUS);
> if (status & S_GENI_CMD_ACTIVE)
> qcom_geni_serial_stop_rx(uport);
>
> - /*
> - * Ensure setup command write is not re-ordered before checking
> - * the status of the Secondary Sequencer.
> - */
> - mb();
> -
mmm, good deletes.
With the minor line coalescing fixed you can add my:
Reviewed-by: Evan Green <evgreen@...omium.org>
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