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@xxxxxxxxxxx/ [2] https://lore.kernel.org/linux-serial/20230605061511.GW14287@xxxxxxxxxxx/ Fixes: 84a9582fd203 ("serial: core: Start managing serial controllers to enable runtime PM") Suggested-by: Tony Lindgren <tony@xxxxxxxxxxx> Signed-off-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx> --- drivers/tty/serial/8250/8250_mtk.c | 50 ++++++------------------------ 1 file changed, 10 insertions(+), 40 deletions(-) diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c index aa8e98164d68..74da5676ce67 100644 --- a/drivers/tty/serial/8250/8250_mtk.c +++ b/drivers/tty/serial/8250/8250_mtk.c @@ -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--; - } + clk_disable_unprepare(data->bus_clk); 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); + 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; } -- 2.41.0.rc0.172.g3f132b7071-goog
