Commit b6c7ff26 authored by Chen-Yu Tsai's avatar Chen-Yu Tsai Committed by Greg Kroah-Hartman
Browse files

serial: 8250_mtk: Simplify clock sequencing and runtime PM 

The 8250_mtk driver's runtime PM support has some issues:

- The bus clock is enabled (through runtime PM callback) later than a
  register write
- runtime PM resume callback directly called in probe, but no
  pm_runtime_set_active() call is present
- UART PM function calls the callbacks directly, _and_ calls runtime
  PM API
- runtime PM callbacks try to do reference counting, adding yet another
  count between runtime PM and clocks

This fragile setup worked in a way, but broke recently with runtime PM
support added to the serial core. The system would hang when the UART
console was probed and brought up.

Tony provided some potential fixes [1][2], though they were still a bit
complicated. The 8250_dw driver, which the 8250_mtk driver might have
been based on, has a similar structure but simpler runtime PM usage.

Simplify clock sequencing and runtime PM support in the 8250_mtk driver.
Specifically, the clock is acquired enabled and assumed to be active,
unless toggled through runtime PM suspend/resume. Reference counting is
removed and left to the runtime PM core. The serial pm function now
only calls the runtime PM API.

[1] https://lore.kernel.org/linux-serial/20230602092701.GP14287@atomide.com/
[2] https://lore.kernel.org/linux-serial/20230605061511.GW14287@atomide.com/



Fixes: 84a9582f ("serial: core: Start managing serial controllers to enable runtime PM")
Suggested-by: default avatarTony Lindgren <tony@atomide.com>
Signed-off-by: default avatarChen-Yu Tsai <wenst@chromium.org>
Reviewed-by: default avatarAngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: default avatarTony Lindgren <tony@atomide.com>
Message-ID: <20230606091747.2031168-1-wenst@chromium.org>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 643662d1

drivers/tty/serial/8250/8250_mtk.c

+10 −40
Original line number Diff line number Diff line
@@ -431,12 +431,7 @@ static int __maybe_unused mtk8250_runtime_suspend(struct device *dev) 
	while

		(serial_in(up, MTK_UART_DEBUG0));



	if (data->clk_count == 0U) {

		dev_dbg(dev, "%s clock count is 0\n", __func__);

	} else {

	clk_disable_unprepare(data->bus_clk);

		data->clk_count--;

	}



	return 0;

}
@@ -444,19 +439,8 @@ static int __maybe_unused mtk8250_runtime_suspend(struct device *dev) 
static int __maybe_unused mtk8250_runtime_resume(struct device *dev)

{

	struct mtk8250_data *data = dev_get_drvdata(dev);

	int err;



	if (data->clk_count > 0U) {

		dev_dbg(dev, "%s clock count is %d\n", __func__,

			data->clk_count);

	} else {

		err = clk_prepare_enable(data->bus_clk);

		if (err) {

			dev_warn(dev, "Can't enable bus clock\n");

			return err;

		}

		data->clk_count++;

	}

	clk_prepare_enable(data->bus_clk);



	return 0;

}
@@ -465,14 +449,12 @@ static void 
mtk8250_do_pm(struct uart_port *port, unsigned int state, unsigned int old)

{

	if (!state)

		if (!mtk8250_runtime_resume(port->dev))

		pm_runtime_get_sync(port->dev);



	serial8250_do_pm(port, state, old);



	if (state)

		if (!pm_runtime_put_sync_suspend(port->dev))

			mtk8250_runtime_suspend(port->dev);

		pm_runtime_put_sync_suspend(port->dev);

}



#ifdef CONFIG_SERIAL_8250_DMA
@@ -504,7 +486,7 @@ static int mtk8250_probe_of(struct platform_device *pdev, struct uart_port *p, 
		return 0;

	}



	data->bus_clk = devm_clk_get(&pdev->dev, "bus");

	data->bus_clk = devm_clk_get_enabled(&pdev->dev, "bus");

	if (IS_ERR(data->bus_clk))

		return PTR_ERR(data->bus_clk);
@@ -587,25 +569,16 @@ static int mtk8250_probe(struct platform_device *pdev) 


	platform_set_drvdata(pdev, data);



	pm_runtime_enable(&pdev->dev);

	err = mtk8250_runtime_resume(&pdev->dev);

	if (err)

		goto err_pm_disable;



	data->line = serial8250_register_8250_port(&uart);

	if (data->line < 0) {

		err = data->line;

		goto err_pm_disable;

	}

	if (data->line < 0)

		return data->line;



	data->rx_wakeup_irq = platform_get_irq_optional(pdev, 1);



	return 0;



err_pm_disable:

	pm_runtime_disable(&pdev->dev);

	pm_runtime_set_active(&pdev->dev);

	pm_runtime_enable(&pdev->dev);



	return err;

	return 0;

}



static int mtk8250_remove(struct platform_device *pdev)
@@ -619,9 +592,6 @@ static int mtk8250_remove(struct platform_device *pdev) 
	pm_runtime_disable(&pdev->dev);

	pm_runtime_put_noidle(&pdev->dev);



	if (!pm_runtime_status_suspended(&pdev->dev))

		mtk8250_runtime_suspend(&pdev->dev);



	return 0;

}