linux-kernel - Re: [PATCH v2] media: i2c: imx412: wait for NVM read (T7) before programming mode registers

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Message-ID: <aWS5qIA1Hfrr-3Yb@kekkonen.localdomain>
Date: Mon, 12 Jan 2026 11:06:48 +0200
From: Sakari Ailus <sakari.ailus@...ux.intel.com>
To: Wenmeng Liu <wenmeng.liu@....qualcomm.com>
Cc: Bryan O'Donoghue <bod@...nel.org>, mchehab@...nel.org,
	linux-media@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] media: i2c: imx412: wait for NVM read (T7) before
 programming mode registers

Hi Wenmeng, Bryan,

On Mon, Jan 12, 2026 at 11:07:39AM +0800, Wenmeng Liu wrote:
> 
> 
> On 1/9/2026 8:32 PM, Bryan O'Donoghue wrote:
> > This delay should go at the end of the operation that requires the delay
> > not at the start of the streaming operation.

I would have thought that, too, but I understand there's an issue with an
Arducam module. It's also not exactly clear to me if all other registers
are writable at the sensor identification time or is the required delay
only concerning starting streaming (I'd hope so).

Also see
<URL:https://git.retiisi.eu/?p=~sailus/linux.git;a=shortlog;h=refs/heads/pm-resume-delay>.
I haven't posted these yet, but I think it'd be useful to avoid extra
delays here and elsewhere.

> > 
> > The delay after the stream write, should be related to the stream write
> > command, not the antecedent - the command that came before
> > start_streaming.
> > 
> > Basically I think you need to put your delay into the CCI_ID read NVM
> > parameter load routine so that it guarantees its own completion.
> > 
> > Because for argument's sake if start_streaming() were not to be the
> > thing to happen after CCI_ID/NVM loading, the logic would no longer
> > work.
> > 
> > And you need a Fixes: tag for this patch too.
> 
> Reading the sensor ID only occurs during the sensor probe process. After the
> probe is completed, the IMX577 will power down. When stream on occurs, the
> driver will power on again and then start streaming, but the sensor ID is
> not read during the stream on process.I have tested this change on imx577
> modules of different models.
> 
> So this change can only happen during power on or stream on.
> 
> Hi Bryan, Sakari,
> May I ask if you have any suggestions regarding this?

Could you add a comment this delay is there for the Arducam module (and
which one), that doesn't work without it?

-- 
Kind regards,

Sakari Ailus