Re: [PATCH v3 4/5] media: i2c: imx412: Add imx477 compatible string

From: Sakari Ailus <sakari.ailus@iki.fi>
To: Bryan O'Donoghue <bryan.odonoghue@linaro.org>
Cc: Dave Stevenson <dave.stevenson@raspberrypi.com>,
	jacopo@jmondi.org, paul.j.murphy@intel.com,
	daniele.alessandrelli@intel.com, mchehab@kernel.org,
	linux-media@vger.kernel.org
Subject: Re: [PATCH v3 4/5] media: i2c: imx412: Add imx477 compatible string
Date: Fri, 16 Sep 2022 14:03:11 +0300	[thread overview]
Message-ID: <YyRX78PH/3zSCdCU@valkosipuli.retiisi.eu> (raw)
In-Reply-To: <e29e5573-13b6-0a29-20c7-ba780d825a37@linaro.org>

Hi Bryan,

On Fri, Sep 16, 2022 at 01:32:06AM +0100, Bryan O'Donoghue wrote:
> On 15/09/2022 23:03, Dave Stevenson wrote:
> > Hi Bryan
> > 
> > On Thu, 15 Sept 2022 at 01:36, Bryan O'Donoghue
> > <bryan.odonoghue@linaro.org> wrote:
> > > 
> > > The Sony imx477 uses the same silicon enabling reference code from Sony in
> > > the available examples provided.
> > 
> > Have you had any conversations with Sony on whether the same register
> > settings are genuinely valid for all of these sensors?
> 
> There's alot to unpack here but... this shows me the main thing
> 
> https://github.com/raspberrypi/linux/blob/rpi-5.15.y/drivers/media/i2c/imx477.c#L37
> 
> The vendor driver reference code I have expects 0x0577. I've discussed with
> Daniele previously - that imx412 and imx577 both return 0x0577 in the chip
> id field and this imx412.c driver won't work with any chip reporting
> anything else.
> 
> Your chip though is returning 0x0477 so it will need to have its own
> upstream driver anyway.

That doesn't matter. What does however matter is what that sensor does and
how it's controlled. It is entirely possible that earlier versions of such
a sensor simply report a wrong ID.

> 
> So the conclusion I drew from the Nvidia/Leopard stack is wrong they call
> the driver imx477 but pointedly and suspiciously comment out the check for
> chip id.
> 
> And its pretty clear why, its so the "imx477" driver they have with work
> with chips identifying as 0x0577 and 0x0477.

I wouldn't be so worried about the model ID *if* the registers (and their
values) programmed to the sensor are otherwise the same.

And even if you have small differences in the registers you'll need to
write there, you can still differentiate between the sensors based on the
compatible string.

I don't have strong opinion on the grey areas though. Still if the register
set is exactly the same, then the driver should also be the same.

-- 
Kind regards,

Sakari Ailus