linux-kernel - Re: [PATCH v3 3/3] media: verisilicon: Avoid G2 bus error while decoding H.264 and HEVC

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Message-ID: <aTL1NrZyeq8g/4Ft@lizhi-Precision-Tower-5810>
Date: Fri, 5 Dec 2025 10:07:34 -0500
From: Frank Li <Frank.li@....com>
To: Nicolas Dufresne <nicolas@...fresne.ca>
Cc: ming.qian@....nxp.com, linux-media@...r.kernel.org, mchehab@...nel.org,
	hverkuil-cisco@...all.nl, benjamin.gaignard@...labora.com,
	p.zabel@...gutronix.de, sebastian.fricke@...labora.com,
	shawnguo@...nel.org, ulf.hansson@...aro.org, s.hauer@...gutronix.de,
	kernel@...gutronix.de, festevam@...il.com, linux-imx@....com,
	l.stach@...gutronix.de, peng.fan@....com, eagle.zhou@....com,
	imx@...ts.linux.dev, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 3/3] media: verisilicon: Avoid G2 bus error while
 decoding H.264 and HEVC

On Thu, Dec 04, 2025 at 07:05:01PM -0500, Nicolas Dufresne wrote:
> Le jeudi 04 décembre 2025 à 17:57 -0500, Frank Li a écrit :
> > On Thu, Dec 04, 2025 at 01:15:35PM -0500, Nicolas Dufresne wrote:
> > > Hi Frank,
> > >
> > > Le jeudi 04 décembre 2025 à 12:34 -0500, Frank Li a écrit :
> > > > > +static struct v4l2_m2m_dev *hantro_get_v4l2_m2m_dev(struct hantro_dev *vpu)
> > > > > +{
> > > > > +	struct device_node *node;
> > > > > +	struct hantro_dev *shared_vpu;
> > > > > +
> > > > > +	if (!vpu->variant || !vpu->variant->shared_devices)
> > > > > +		goto init_new_m2m_dev;
> > > >
> > > > I found only use shared_devices here, how to  ensure that g1 and g2 operate
> > > > alternately by using shared_devices?
> > >
> > > shared_devices is an array of of_device_id we match against. All the matching
> > > devices will share the same v4l2_m2m_dev (aka m2m scheduler). Typically, both
> > > cores will be schedule as one. This achieve what alternate operations without
> > > active polling or blocking locks/mutex.
> >
> > Okay, but this code require shared_devices==NULL's device probe firstly.
> > generally not order guaranteed, if there are not depentance at DT.
>
> shared_devices is a constant array that is set inside the variant. It is
> normally NULL, except for the imx8mq SoC, for which its always set.
>
> >
> > Does VPU always probe before g1/g2?
> >
> > and if there are two VPU instances, what's happen?
>
> Since there is two VPU, g1 and g2, we will enter this loop:
>
> > +	for_each_matching_node(node, vpu->variant->shared_devices) {
>
> On imx8mq, this will match twice.
>
> > +		struct platform_device *pdev;
> > +		struct v4l2_m2m_dev *m2m_dev;
> > +
> > +		pdev = of_find_device_by_node(node);
> > +		of_node_put(node);
> > +
> > +		if (!pdev)
> > +			continue;
>
> If the match does not have a device yet (not probe yet), we skip.
>
> > +
> > +		shared_vpu = platform_get_drvdata(pdev);
> > +		if (IS_ERR_OR_NULL(shared_vpu) || shared_vpu == vpu) {
> > +			platform_device_put(pdev);
> > +			continue;
> > +		}
>
> If its the current VPU, we also skip.
>
> > +
> > +		v4l2_m2m_get(shared_vpu->m2m_dev);
> > +		m2m_dev = shared_vpu->m2m_dev;
> > +		platform_device_put(pdev);
>
> Finally, if the other VPU was initialized, we ref the v4l2_m2m_dev. We will then
> create m2m_ctx from it which will cause the two VPU to be scheduled one after
> the other.
>
> > +
> > +		return m2m_dev;
> > +	}
>
> > +
> > +init_new_m2m_dev:
> > +	return v4l2_m2m_init(&vpu_m2m_ops);
>
> Otherwhise we create a fresh one.
>
> Does it make sense now ?

Yes, thanks for detial explain.

Frank

>
> Nicolas