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: <aTIRwcocnye0Y6yV@lizhi-Precision-Tower-5810>
Date: Thu, 4 Dec 2025 17:57:05 -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 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.

Does VPU always probe before g1/g2?

and if there are two VPU instances, what's happen?

Frank

>
> For this platform, we only matched against the compatible for simplicity, since
> we know there is only one of each type. I've suggested this method to Ming,
> since it will make it really easy to apply such a quirk if other hardware have
> problems or design constraints.
>
> regards,
> Nicolas