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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: 84a9582fd2 ("serial: core: Start managing serial controllers to enable runtime PM")
Suggested-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: Tony Lindgren <tony@atomide.com>
Message-ID: <20230606091747.2031168-1-wenst@chromium.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Chen-Yu Tsai 2023-06-06 17:17:45 +08:00 committed by Greg Kroah-Hartman
parent 643662d12b
commit b6c7ff2693
1 changed files with 10 additions and 40 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

50
drivers/tty/serial/8250/8250_mtk.c
View File

@ -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);
pm_runtime_set_active(&pdev->dev);
pm_runtime_enable(&pdev->dev);
return 0;
err_pm_disable:
pm_runtime_disable(&pdev->dev);
return err;
}
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;
}