Re: [PATCH v4 13/20] soc: starfive: Add jh7110-vout-subsystem driver

[Icenowy Zheng <zhengxingda@iscas.ac.cn>]

在 2026-09-15二的 17:32 +0200，Michal Wilczynski写道：
> Nothing in the video output subsystem can reach its own registers
> until
> the NoC display bus clock and reset are up and PD_VOUT is powered,
> and
> those are shared by every device in the region. Leaving them to
> whichever
> consumer probes first works by accident and stops working as soon as
> the
> probe order changes.
> 
> Add a driver for the subsystem node that takes the bus clock and
> reset,
> holds a runtime PM reference so genpd keeps PD_VOUT powered, and then
> populates its children. All three are released only once the last
> child
> is gone.
> 
> Signed-off-by: Michal Wilczynski <m.wilczynski@samsung.com>

```
Tested-by: Icenowy Zheng <zhengxingda@iscas.ac.cn>
```

Thanks,
Icenowy

> ---
>  drivers/soc/starfive/Kconfig                 | 15 +++++
>  drivers/soc/starfive/Makefile                |  1 +
>  drivers/soc/starfive/jh7110-vout-subsystem.c | 82
> ++++++++++++++++++++++++++++
>  3 files changed, 98 insertions(+)
> 
> diff --git a/drivers/soc/starfive/Kconfig
> b/drivers/soc/starfive/Kconfig
> index
> e738638ab0f755fbbabca259264abb56f3b6101f..cf5e626b8a39a75768917eee188
> a79256b36f1aa 100644
> --- a/drivers/soc/starfive/Kconfig
> +++ b/drivers/soc/starfive/Kconfig
> @@ -6,6 +6,21 @@
>  if ARCH_STARFIVE || COMPILE_TEST
>  menu "Starfive SoC drivers"
>  
> +config SOC_STARFIVE_JH7110_VOUT_SUBSYSTEM
> +	tristate "StarFive JH7110 video output subsystem driver"
> +	depends on OF
> +	select PM
> +	help
> +	  This option enables the parent driver for the StarFive
> JH7110
> +	  video output subsystem, which the documentation calls
> dom_vout_top.
> +
> +	  The subsystem covers the DC8200 display controller, the
> HDMI
> +	  transmitter, the video output clock generator and the
> video output
> +	  system controller. They share one NoC port whose clock and
> reset
> +	  gate access to the whole register region, and the region
> sits in
> +	  the PD_VOUT power domain. This driver owns those resources
> and
> +	  holds them for as long as any of its children exist.
> +
>  config SOC_STARFIVE_JH7110_HDMI_SUBSYSTEM
>  	tristate "StarFive JH7110 HDMI subsystem driver"
>  	depends on OF
> diff --git a/drivers/soc/starfive/Makefile
> b/drivers/soc/starfive/Makefile
> index
> be89d8119212b7a7038817c2f0e8eac1984ada88..6c229020c1e563b37df43f6ac16
> 65465a11333cc 100644
> --- a/drivers/soc/starfive/Makefile
> +++ b/drivers/soc/starfive/Makefile
> @@ -1,2 +1,3 @@
>  # SPDX-License-Identifier: GPL-2.0-only
>  obj-$(CONFIG_SOC_STARFIVE_JH7110_HDMI_SUBSYSTEM) += jh7110-hdmi-
> subsystem.o
> +obj-$(CONFIG_SOC_STARFIVE_JH7110_VOUT_SUBSYSTEM) += jh7110-vout-
> subsystem.o
> diff --git a/drivers/soc/starfive/jh7110-vout-subsystem.c
> b/drivers/soc/starfive/jh7110-vout-subsystem.c
> new file mode 100644
> index
> 0000000000000000000000000000000000000000..af632692e2139d9d07edd478a29
> 9b170ad1b7104
> --- /dev/null
> +++ b/drivers/soc/starfive/jh7110-vout-subsystem.c
> @@ -0,0 +1,82 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Driver for the StarFive JH7110 video output subsystem
> + *
> + * Copyright (c) 2025 Samsung Electronics Co., Ltd.
> + * Author: Michal Wilczynski <m.wilczynski@samsung.com>
> + *
> + * The display hardware sits behind a single NoC port whose clock
> and reset
> + * gate access to every register in the region, inside the PD_VOUT
> power
> + * domain. Nothing below this node can reach its own registers until
> all three
> + * are up, so bring them up here and hold them for as long as any
> child device
> + * exists, rather than leaving them to whichever consumer happens to
> probe
> + * first.
> + */
> +
> +#include <linux/clk.h>
> +#include <linux/module.h>
> +#include <linux/of_platform.h>
> +#include <linux/platform_device.h>
> +#include <linux/pm_runtime.h>
> +#include <linux/reset.h>
> +
> +static void jh7110_vout_subsys_pm_put(void *data)
> +{
> +	pm_runtime_put_sync(data);
> +}
> +
> +static int jh7110_vout_subsys_probe(struct platform_device *pdev)
> +{
> +	struct device *dev = &pdev->dev;
> +	struct reset_control *bus_rst;
> +	struct clk *bus_clk;
> +	int ret;
> +
> +	/*
> +	 * Take a runtime PM reference for the lifetime of this
> device. genpd
> +	 * only keeps PD_VOUT powered while something actually holds
> it, and
> +	 * an unclocked or unpowered access to this region wedges
> the bus.
> +	 */
> +	ret = devm_pm_runtime_enable(dev);
> +	if (ret)
> +		return ret;
> +
> +	ret = pm_runtime_resume_and_get(dev);
> +	if (ret)
> +		return dev_err_probe(dev, ret, "Failed to power on
> PD_VOUT\n");
> +
> +	ret = devm_add_action_or_reset(dev,
> jh7110_vout_subsys_pm_put, dev);
> +	if (ret)
> +		return ret;
> +
> +	bus_clk = devm_clk_get_enabled(dev, NULL);
> +	if (IS_ERR(bus_clk))
> +		return dev_err_probe(dev, PTR_ERR(bus_clk),
> +				     "Failed to enable NoC bus
> clock\n");
> +
> +	bus_rst = devm_reset_control_get_exclusive_deasserted(dev,
> NULL);
> +	if (IS_ERR(bus_rst))
> +		return dev_err_probe(dev, PTR_ERR(bus_rst),
> +				     "Failed to deassert NoC bus
> reset\n");
> +
> +	return devm_of_platform_populate(dev);
> +}
> +
> +static const struct of_device_id jh7110_vout_subsys_of_match[] = {
> +	{ .compatible = "starfive,jh7110-vout-subsystem", },
> +	{ /* sentinel */ }
> +};
> +MODULE_DEVICE_TABLE(of, jh7110_vout_subsys_of_match);
> +
> +static struct platform_driver jh7110_vout_subsys_driver = {
> +	.probe = jh7110_vout_subsys_probe,
> +	.driver = {
> +		.name = "jh7110-vout-subsystem",
> +		.of_match_table = jh7110_vout_subsys_of_match,
> +	},
> +};
> +module_platform_driver(jh7110_vout_subsys_driver);
> +
> +MODULE_AUTHOR("Michal Wilczynski <m.wilczynski@samsung.com>");
> +MODULE_DESCRIPTION("StarFive JH7110 video output subsystem driver");
> +MODULE_LICENSE("GPL");