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    SubjectRe: [PATCH V3 4/6] tty: serial: meson: The UART baud rate calculation is described using the common clock code. Also added S4 chip uart Compatible.
    On Thu, Dec 30, 2021 at 11:21 AM Yu Tu <yu.tu@amlogic.com> wrote:
    [...]
    > @@ -270,14 +284,11 @@ static void meson_uart_reset(struct uart_port *port)
    > static int meson_uart_startup(struct uart_port *port)
    > {
    > u32 val;
    > - int ret = 0;
    > + int ret;
    >
    > - val = readl(port->membase + AML_UART_CONTROL);
    > - val |= AML_UART_CLEAR_ERR;
    > - writel(val, port->membase + AML_UART_CONTROL);
    > - val &= ~AML_UART_CLEAR_ERR;
    > - writel(val, port->membase + AML_UART_CONTROL);
    > + meson_uart_reset(port);
    I suggest splitting this into a separate patch. In general I think
    it's a good idea to re-use meson_uart_reset here if possible.
    However, if during testing it turns out that this doesn't work then we
    can revert this single patch which updates meson_uart_startup() only -
    instead of reverting the whole transition to the common clock
    framework.

    [...]
    > static int meson_uart_request_port(struct uart_port *port)
    > {
    > + struct meson_uart_data *private_data = port->private_data;
    > + int ret;
    > +
    > + ret = clk_prepare_enable(private_data->pclk);
    > + if (ret)
    > + return ret;
    > +
    > + ret = clk_prepare_enable(private_data->baud_clk);
    > + if (ret) {
    > + clk_disable_unprepare(private_data->pclk);
    > + return ret;
    > + }
    This code is from my original suggestion - and I had a doubt there
    which I forgot to add as a comment originally:
    Can you confirm that accessing the UART controller registers works
    even when "pclk" is turned off?
    I am asking this because the common clock framework can access the
    clocks at any time.
    And I have seen SoCs which would hang when trying to access a module's
    registers while the module's pclk is turned off.

    [...]
    > port->fifosize = 64;
    commit 27d44e05d7b85d ("tty: serial: meson: retrieve port FIFO size
    from DT") [0] from May 2021 has changed this line to:
    port->fifosize = fifosize;
    So your patch currently does not apply to linux-next (or even Linus'
    mainline tree).

    [...]
    > static const struct of_device_id meson_uart_dt_match[] = {
    > - { .compatible = "amlogic,meson6-uart" },
    > - { .compatible = "amlogic,meson8-uart" },
    > - { .compatible = "amlogic,meson8b-uart" },
    > - { .compatible = "amlogic,meson-gx-uart" },
    > + {
    > + .compatible = "amlogic,meson6-uart",
    > + .data = (void *)false,
    > + },
    > + {
    > + .compatible = "amlogic,meson8-uart",
    > + .data = (void *)false,
    > + },
    > + {
    > + .compatible = "amlogic,meson8b-uart",
    > + .data = (void *)false,
    > + },
    > + {
    > + .compatible = "amlogic,meson-gxbb-uart",
    > + .data = (void *)false,
    > + },
    > + {
    > + .compatible = "amlogic,meson-gxl-uart",
    > + .data = (void *)true,
    > + },
    > + {
    > + .compatible = "amlogic,meson-g12a-uart",
    > + .data = (void *)true,
    > + },
    > + {
    > + .compatible = "amlogic,meson-s4-uart",
    > + .data = (void *)true,
    > + },
    > + /*
    > + * deprecated, don't use anymore because it doesn't differentiate
    > + * between GXBB and GXL which have different revisions of the UART IP.
    > + */
    > + {
    > + .compatible = "amlogic,meson-gx-uart",
    > + .data = (void *)false,
    > + },
    For this change I think it's also best to split it into separate
    changes, similar to the dt-bindings:
    1) deprecate and replace "amlogic,meson-gx-uart"
    2) another one to add the S4 compatible string
    3) and a third one with the big common clock framework change (adding
    the .data attributes)

    This is about the "Separate each logical change into a separate patch"
    rule from the Linux kernel patch submission guide [1]
    Also I hope that it will make it (at least a bit) easier for others to
    also review this patch.


    Best regards,
    Martin


    [0] https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/drivers/tty/serial/meson_uart.c?id=27d44e05d7b85d9d4cfe0a3c0663ea49752ece93
    [1] https://www.kernel.org/doc/html/v4.17/process/submitting-patches.html#separate-your-changes

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