Re: [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.

From: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
To: Yu Tu <yu.tu@amlogic.com>
Cc: linux-serial@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-amlogic@lists.infradead.org, linux-kernel@vger.kernel.org,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Jiri Slaby <jirislaby@kernel.org>,
	Neil Armstrong <narmstrong@baylibre.com>,
	Vyacheslav <adeep@lexina.in>, Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>
Subject: Re: [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.
Date: Fri, 31 Dec 2021 00:13:36 +0100	[thread overview]
Message-ID: <CAFBinCCL-QaeSRCLzfyNXcRQZ7YC1D85rP2y4OGkAjCmQEqGgQ@mail.gmail.com> (raw)
In-Reply-To: <20211230102110.3861-5-yu.tu@amlogic.com>

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