Re: [PATCH v2] pmdomain: imx8m-blk-ctrl: Serialize power on/off across sibling domains

[Frank Li]

On Thu, Sep 17, 2026 at 04:07:54PM +0900, Ming Qian wrote:
> On i.MX8MP the VPU blk-ctrl exposes G1, G2 and VC8000E as three separate
> genpds, each serialized only by its own genpd lock, so their power_on and
> power_off callbacks can run concurrently on SMP.
>
> The sequences are not independent: they share the VPUMIX bus domain, the
> VPU_NOC and the ADB400 handshake. On power up the GPC cannot ack-verify
> the ADB400 handshake - the ack only completes once blk-ctrl sets the bus
> clk-en bit - so it just waits a fixed delay instead of polling hskack. A
> sibling transition landing inside another domain's reset window disturbs
> that shared clock and handshake timing, the victim's reset does not take
> effect, and its block registers read back all zeros: the decoder times
> out or the encoder fails its format check.
>
> Serialize the blk-ctrl reset sequence with a per-blk-ctrl mutex; the
> driver deliberately avoids a genpd hierarchy, so the genpd core gives no
> cross-sibling serialization.
>
> Fixes: a1a5f15f7f6c ("soc: imx: imx8m-blk-ctrl: add i.MX8MP VPU blk ctrl")
> Signed-off-by: Ming Qian <ming.qian@xxxxxxxxxxx>
> ---
> Problem:
> On i.MX8MP, running the VC8000E encoder and the G1/G2 decoders
> concurrently rarely and non-deterministically leaves a VPU stuck in
> reset: its block registers read back all zeros. A decoder then times out
> or the encoder fails its format check.
>
> Root cause:
> The VPU blk-ctrl exposes G1, G2 and VC8000E as three separate genpds,
> serialized only by the per-genpd lock, so on SMP their power_on/power_off
> callbacks can run concurrently. The sequences share the VPUMIX bus
> domain, the VPU_NOC and the ADB400 handshake. On power up the GPC does
> not ack-verify the ADB400 handshake - the ack only completes once
> blk-ctrl sets the bus clk-en bit - so it just waits a fixed delay. A
> sibling transition landing inside another domain's reset window disturbs
> that shared clock and handshake timing, the victim's reset fails to take
> effect, and its block is left in reset with registers reading zero.
>
> Fix:
> Serialize the blk-ctrl reset sequence with a per-blk-ctrl mutex, so a
> sibling domain cannot run its sequence while another is inside its reset
> window. The driver deliberately avoids a genpd hierarchy, so the genpd
> core provides no cross-sibling serialization.
>
> Test:
> i.MX8MP, Android 6.18 kernel, concurrent H.264 decode and encode. Without
> this patch the failure reproduces within one to two hours. With it the
> same test ran overnight, over 14 hours, without a single occurrence.
> ---
> Changes in v2:
> - Replace guard(mutex) with explicit mutex_lock()/mutex_unlock():
>   power_on() already unwinds errors with goto, and cleanup.h asks not to
>   mix goto and scope-based cleanup in one function (sashiko-bot).
> - Shorten the commit message to the essentials and move the detailed
>   hardware analysis into this cover letter (Frank Li).
> - Link to v1: https://patch.msgid.link/20260915-imx8mp-blk-ctrl-v1-1-b3b4e6e7e676@xxxxxxxxxxx
>
> To: Ulf Hansson <ulfh@xxxxxxxxxx>
> To: Frank Li <Frank.Li@xxxxxxx>
> To: Sascha Hauer <s.hauer@xxxxxxxxxxxxxx>
> To: Pengutronix Kernel Team <kernel@xxxxxxxxxxxxxx>
> To: Fabio Estevam <festevam@xxxxxxxxx>
> To: Shawn Guo <shawnguo@xxxxxxxxxx>
> To: Peng Fan <peng.fan@xxxxxxx>
> Cc: linux-pm@xxxxxxxxxxxxxxx
> Cc: imx@xxxxxxxxxxxxxxx
> Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx
> ---
>  drivers/pmdomain/imx/imx8m-blk-ctrl.c | 23 ++++++++++++++++++++++-
>  1 file changed, 22 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/pmdomain/imx/imx8m-blk-ctrl.c b/drivers/pmdomain/imx/imx8m-blk-ctrl.c
> index 479789009c7f..270f43229fe7 100644
> --- a/drivers/pmdomain/imx/imx8m-blk-ctrl.c
> +++ b/drivers/pmdomain/imx/imx8m-blk-ctrl.c
> @@ -15,6 +15,7 @@
>  #include <linux/pm_runtime.h>
>  #include <linux/regmap.h>
>  #include <linux/clk.h>
> +#include <linux/mutex.h>
>
>  #include <dt-bindings/power/imx8mm-power.h>
>  #include <dt-bindings/power/imx8mn-power.h>
> @@ -34,6 +35,12 @@ struct imx8m_blk_ctrl {
>  	struct regmap *regmap;
>  	struct imx8m_blk_ctrl_domain *domains;
>  	struct genpd_onecell_data onecell_data;
> +	/*
> +	 * Serializes the blk-ctrl reset/clock sequence across sibling domains;
> +	 * their transitions interact through the shared VPUMIX bus domain,
> +	 * VPU_NOC and the not-ack-verified ADB400 handshake (ERR050531).
> +	 */
> +	struct mutex power_lock;
>  };
>
>  struct imx8m_blk_ctrl_domain_data {
> @@ -98,12 +105,14 @@ static int imx8m_blk_ctrl_power_on(struct generic_pm_domain *genpd)
>  	struct imx8m_blk_ctrl *bc = domain->bc;
>  	int ret;
>
> +	mutex_lock(&bc->power_lock);
> +
>  	/* make sure bus domain is awake */
>  	ret = pm_runtime_get_sync(bc->bus_power_dev);
>  	if (ret < 0) {
>  		pm_runtime_put_noidle(bc->bus_power_dev);
>  		dev_err(bc->dev, "failed to power up bus domain\n");
> -		return ret;
> +		goto unlock;

can you use auto cleanup guard()

Frank

>  	}
>
>  	/* put devices into reset */
> @@ -148,12 +157,16 @@ static int imx8m_blk_ctrl_power_on(struct generic_pm_domain *genpd)
>  	/* disable upstream clocks */
>  	clk_bulk_disable_unprepare(data->num_clks, domain->clks);
>
> +	mutex_unlock(&bc->power_lock);
> +
>  	return 0;
>
>  clk_disable:
>  	clk_bulk_disable_unprepare(data->num_clks, domain->clks);
>  bus_put:
>  	pm_runtime_put(bc->bus_power_dev);
> +unlock:
> +	mutex_unlock(&bc->power_lock);
>
>  	return ret;
>  }
> @@ -164,6 +177,8 @@ static int imx8m_blk_ctrl_power_off(struct generic_pm_domain *genpd)
>  	const struct imx8m_blk_ctrl_domain_data *data = domain->data;
>  	struct imx8m_blk_ctrl *bc = domain->bc;
>
> +	mutex_lock(&bc->power_lock);
> +
>  	/* put devices into reset and disable clocks */
>  	if (data->mipi_phy_rst_mask)
>  		regmap_clear_bits(bc->regmap, BLK_MIPI_RESET_DIV, data->mipi_phy_rst_mask);
> @@ -177,6 +192,8 @@ static int imx8m_blk_ctrl_power_off(struct generic_pm_domain *genpd)
>  	/* allow bus domain to suspend */
>  	pm_runtime_put(bc->bus_power_dev);
>
> +	mutex_unlock(&bc->power_lock);
> +
>  	return 0;
>  }
>
> @@ -202,6 +219,10 @@ static int imx8m_blk_ctrl_probe(struct platform_device *pdev)
>
>  	bc->dev = dev;
>
> +	ret = devm_mutex_init(dev, &bc->power_lock);
> +	if (ret)
> +		return ret;
> +
>  	bc_data = of_device_get_match_data(dev);
>
>  	base = devm_platform_ioremap_resource(pdev, 0);
>
> ---
> base-commit: 27953c044974baf7e24dee3e9342fe0103dea80c
> change-id: 20260911-imx8mp-blk-ctrl-c46f26783073
>
>