Re: [PATCH v3] drm/bridge: ti-sn65dsi86: Check bridge connection failure

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Mon, Mar 24, 2025 at 10:17:05AM -0700, Doug Anderson wrote:
> On Mon, Mar 24, 2025 at 9:40 AM Laurent Pinchart wrote:
> > On Tue, Mar 18, 2025 at 10:00:31PM +0100, Wolfram Sang wrote:
> > > Hi Laurent,
> > >
> > > > > Read out and check the ID registers, so we can bail out if I2C
> > > > > communication does not work or if the device is unknown.
> > > >
> > > > What's the advantage of that, what are you trying to guard against ?
> > >
> > > That a random chip at address 0x2c will be used.
> >
> > Is that really a problem ? That would only occur with a broken DT, is it
> > worth guarding against a development-time issue with a runtime check
> > that will increase boot time for every user ?
> 
> FWIW, this can also happen simply due to broken / damaged hardware. If
> a board gets stressed and causes a pin to become disconnected or if a
> regulator ages and stops providing power then we can also end up in
> this state. Getting a nice obvious error at probe when the device
> isn't responding at all can make problems like this much easier to
> debug.

I'm not fully convinced it's worth it, compared to an error at runtime,
and especially given that there are way more pins than supplies or
SCL/SDA that could suffer from a similar issue. I won't block the patch,
but I think it's overkill.

> It's not uncommon for i2c devices to probe to make sure the
> device is really there at bootup. Checking for the full 8-byte ID is
> probably a bit overkill, but at the same time if we're going to probe
> something the ID is not a terrible thing to probe and reading 8 bytes
> won't really take much longer than reading 1.

-- 
Regards,

Laurent Pinchart