linux-kernel - Re: [PATCH v8 13/17] media: rkvdec: Disable multicore support

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Message-ID: <dff8d7889655ccc0f1808847879fb5afb654f10c.camel@collabora.com>
Date: Sun, 18 Jan 2026 17:13:44 -0500
From: Nicolas Dufresne <nicolas.dufresne@...labora.com>
To: Detlev Casanova <detlev.casanova@...labora.com>, 
	linux-kernel@...r.kernel.org
Cc: Mauro Carvalho Chehab <mchehab@...nel.org>, Ezequiel Garcia	
 <ezequiel@...guardiasur.com.ar>, Heiko Stuebner <heiko@...ech.de>, Ricardo
 Ribalda <ribalda@...omium.org>, Hans Verkuil <hverkuil@...nel.org>, Hans de
 Goede <hansg@...nel.org>,  Yunke Cao <yunkec@...gle.com>, Jonathan Corbet
 <corbet@....net>, Laurent Pinchart	 <laurent.pinchart@...asonboard.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,  James Cowgill
 <james.cowgill@...ize.com>, linux-media@...r.kernel.org,
 linux-rockchip@...ts.infradead.org, 	linux-arm-kernel@...ts.infradead.org,
 kernel@...labora.com, Jonas Karlman	 <jonas@...boo.se>, Diederik de Haas
 <didi.debian@...ow.org>
Subject: Re: [PATCH v8 13/17] media: rkvdec: Disable multicore support

Le vendredi 09 janvier 2026 à 11:15 -0500, Detlev Casanova a écrit :
> Similarly to what is done in Hantro, avoid exposing equal video codecs to
> userspace. Equal video codecs allow scheduling work between the cores.
> For that kernel support is required, which does not yet exist.
> Until that is implemented, avoid exposing each core separately to
> userspace so that multicore can be added in the future without breaking
> userspace ABI.
> 
> This currently applies only to RK3588 which has 2 equal VDPU381 decoders,
> but will be applied for all SoC supported by rkvdec that has multiple DTS
> nodes with the same compatible.
> 
> Signed-off-by: Detlev Casanova <detlev.casanova@...labora.com>

Reviewed-by: Nicolas Dufresne <nicolas.dufresne@...labora.com>

> ---
>  .../media/platform/rockchip/rkvdec/rkvdec.c   | 47 +++++++++++++++++++
>  1 file changed, 47 insertions(+)
> 
> diff --git a/drivers/media/platform/rockchip/rkvdec/rkvdec.c b/drivers/media/platform/rockchip/rkvdec/rkvdec.c
> index ce96a0470d4d..af2eced90026 100644
> --- a/drivers/media/platform/rockchip/rkvdec/rkvdec.c
> +++ b/drivers/media/platform/rockchip/rkvdec/rkvdec.c
> @@ -1269,6 +1269,49 @@ static void rkvdec_watchdog_func(struct work_struct *work)
>  	}
>  }
>  
> +/*
> + * Some SoCs, like RK3588 have multiple identical VDPU cores, but the
> + * kernel is currently missing support for multi-core handling. Exposing
> + * separate devices for each core to userspace is bad, since that does
> + * not allow scheduling tasks properly (and creates ABI). With this workaround
> + * the driver will only probe for the first core and early exit for the other
> + * cores. Once the driver gains multi-core support, the same technique
> + * for detecting the first core can be used to cluster all cores together.
> + */
> +static int rkvdec_disable_multicore(struct rkvdec_dev *rkvdec)
> +{
> +	struct device_node *node = NULL;
> +	const char *compatible;
> +	bool is_first_core;
> +	int ret;
> +
> +	/* Intentionally ignores the fallback strings */
> +	ret = of_property_read_string(rkvdec->dev->of_node, "compatible", &compatible);
> +	if (ret)
> +		return ret;
> +
> +	/* The first compatible and available node found is considered the main core */
> +	do {
> +		node = of_find_compatible_node(node, NULL, compatible);
> +		if (of_device_is_available(node))
> +			break;
> +	} while (node);
> +
> +	if (!node)
> +		return -EINVAL;
> +
> +	is_first_core = (rkvdec->dev->of_node == node);
> +
> +	of_node_put(node);
> +
> +	if (!is_first_core) {
> +		dev_info(rkvdec->dev, "missing multi-core support, ignoring this instance\n");
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
>  static const struct rkvdec_variant_ops rk3399_variant_ops = {
>  	.irq_handler = rk3399_irq_handler,
>  };
> @@ -1332,6 +1375,10 @@ static int rkvdec_probe(struct platform_device *pdev)
>  	mutex_init(&rkvdec->vdev_lock);
>  	INIT_DELAYED_WORK(&rkvdec->watchdog_work, rkvdec_watchdog_func);
>  
> +	ret = rkvdec_disable_multicore(rkvdec);
> +	if (ret)
> +		return ret;
> +
>  	ret = devm_clk_bulk_get_all_enabled(&pdev->dev, &rkvdec->clocks);
>  	if (ret < 0)
>  		return ret;

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