Re: [PATCH v3] serial: 8250_mtk: Enable baud clock and manage in runtime PM
From: Matthias Brugger <matthias.bgg@gmail.com>
Date: 2025-09-17 10:01:02
Also in:
linux-mediatek, linux-serial, lkml
On 16/09/2025 23:37, Daniel Golle wrote:
Some MediaTek SoCs got a gated UART baud clock, which currently gets
disabled as the clk subsystem believes it would be unused. This results in
the uart freezing right after "clk: Disabling unused clocks" on those
platforms.
Request the baud clock to be prepared and enabled during probe, and to
restore run-time power management capabilities to what it was before commit
e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock
management") disable and unprepare the baud clock when suspending the UART,
prepare and enable it again when resuming it.
Fixes: e32a83c70cf9 ("serial: 8250-mtk: modify mtk uart power and clock management")
Most of the issues from this commit are already fixed in
b6c7ff2693ddc ("serial: 8250_mtk: Simplify clock sequencing and runtime PM")
which is more or less a revert of e32a83c70cf9.
I think we should add
Fixes: b6c7ff2693ddc ("serial: 8250_mtk: Simplify clock sequencing and runtime PM")
here as well. It's a fix of a fix :)
Regards,
Matthias
quoted hunk ↗ jump to hunk
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> Signed-off-by: Daniel Golle <daniel@makrotopia.org> --- v3: squash into single patch v2: add managing run-time PM in dedicated patch drivers/tty/serial/8250/8250_mtk.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-)diff --git a/drivers/tty/serial/8250/8250_mtk.c b/drivers/tty/serial/8250/8250_mtk.c index b44de2ed7413..5875a7b9b4b1 100644 --- a/drivers/tty/serial/8250/8250_mtk.c +++ b/drivers/tty/serial/8250/8250_mtk.c@@ -435,6 +435,7 @@ static int __maybe_unused mtk8250_runtime_suspend(struct device *dev) while (serial_in(up, MTK_UART_DEBUG0)); + clk_disable_unprepare(data->uart_clk); clk_disable_unprepare(data->bus_clk); return 0;@@ -445,6 +446,7 @@ static int __maybe_unused mtk8250_runtime_resume(struct device *dev) struct mtk8250_data *data = dev_get_drvdata(dev); clk_prepare_enable(data->bus_clk); + clk_prepare_enable(data->uart_clk); return 0; }@@ -475,13 +477,13 @@ static int mtk8250_probe_of(struct platform_device *pdev, struct uart_port *p, int dmacnt; #endif - data->uart_clk = devm_clk_get(&pdev->dev, "baud"); + data->uart_clk = devm_clk_get_enabled(&pdev->dev, "baud"); if (IS_ERR(data->uart_clk)) { /* * For compatibility with older device trees try unnamed * clk when no baud clk can be found. */ - data->uart_clk = devm_clk_get(&pdev->dev, NULL); + data->uart_clk = devm_clk_get_enabled(&pdev->dev, NULL); if (IS_ERR(data->uart_clk)) { dev_warn(&pdev->dev, "Can't get uart clock\n"); return PTR_ERR(data->uart_clk);