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From: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
To: Wolfram Sang <wsa@the-dreams.de>
Cc: Luca Ceresoli <luca@lucaceresoli.net>,
	Wolfram Sang <wsa+renesas@sang-engineering.com>,
	linux-i2c@vger.kernel.org, linux-renesas-soc@vger.kernel.org,
	Kieran Bingham <kieran@ksquared.org.uk>,
	Jacopo Mondi <jacopo@jmondi.org>,
	Vladimir Zapolskiy <vz@mleia.com>
Subject: Re: [RFC PATCH 3/5] i2c: core: add function to request an alias
Date: Wed, 8 Jan 2020 15:31:53 +0200	[thread overview]
Message-ID: <20200108133153.GB4884@pendragon.ideasonboard.com> (raw)
In-Reply-To: <20200108132708.GC834@kunai>

On Wed, Jan 08, 2020 at 02:27:08PM +0100, Wolfram Sang wrote:
> 
> > > It would be nice, but I'm not sure this is really doable. Say the DT for
> > > board X lists all the used slave addresses. Then the kernel would assume
> > > all the other addresses are available. But then somebody includes the DT
> > > of board X in the DT for product Z, based on board X + add-on board Y.
> > > Add-on board Y has 2 I2C chips, but only one is described in DT. Now the
> > > kernel still thinks it knows all the used address, but this is wrong.
> > 
> > That's the fault of the system integrator though. We can't prevent
> > people from making incorrect DT, and we shouldn't go to great length to
> > still support them.
> 
> Currently, there is no paradigm that all I2C busses must be fully
> described. Enforcing it now all of a sudden is not too user-friendly,
> or?

We're only enforcing it for systems that want to make use of this new
API, so it's not breaking backward compatibility.

> Especially since calling read_byte once is not necessarily "great
> length" in my book. If you have 8 cameras on a 400kHz bus, the 8 * 18
> bits should take 360us if I am not mistaken?

That's assuming the first scanned address is free. There could also be
I2C-controller I2C muxes or gates in front of the bus. Things can
quickly get more expensive.

-- 
Regards,

Laurent Pinchart

  reply	other threads:[~2020-01-08 13:32 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-31 16:13 [RFC PATCH 0/5] i2c: implement mechanism to retrieve an alias device Wolfram Sang
2019-12-31 16:13 ` [RFC PATCH 1/5] i2c: core: refactor scanning for a client Wolfram Sang
2020-01-01 16:45   ` Laurent Pinchart
2020-01-07  9:26   ` Kieran Bingham
2020-01-07  9:53     ` Geert Uytterhoeven
2020-01-07  9:58       ` Kieran Bingham
2020-01-07 10:25       ` Wolfram Sang
2020-01-07 10:36         ` Geert Uytterhoeven
2020-01-07 11:23           ` Wolfram Sang
2020-01-07 15:03             ` Luca Ceresoli
2020-01-07 16:45               ` Wolfram Sang
2020-01-07 16:52                 ` Kieran Bingham
2019-12-31 16:13 ` [RFC PATCH 2/5] i2c: core: add new variant to check " Wolfram Sang
2020-01-01 16:49   ` Laurent Pinchart
2020-01-07  9:42   ` Kieran Bingham
2019-12-31 16:13 ` [RFC PATCH 3/5] i2c: core: add function to request an alias Wolfram Sang
2020-01-01 16:55   ` Laurent Pinchart
2020-01-02 18:58     ` Luca Ceresoli
2020-01-02 21:13       ` Wolfram Sang
2020-01-02 22:27         ` Luca Ceresoli
2020-01-03  0:10           ` Laurent Pinchart
2020-01-07 15:03             ` Luca Ceresoli
2020-01-07 17:13               ` Laurent Pinchart
2020-01-08 13:27                 ` Wolfram Sang
2020-01-08 13:31                   ` Laurent Pinchart [this message]
2020-01-08 13:38                     ` Wolfram Sang
2020-01-08 13:22               ` Wolfram Sang
2020-01-08 13:19             ` Wolfram Sang
2020-01-08 13:29               ` Geert Uytterhoeven
2020-01-08 13:34               ` Laurent Pinchart
2020-01-02 21:03     ` Wolfram Sang
2020-01-21  9:05     ` Peter Rosin
2020-01-21  9:05       ` Peter Rosin
2020-01-07  9:40   ` Kieran Bingham
2020-01-07 17:11     ` Laurent Pinchart
2020-01-07 17:14       ` Kieran Bingham
2020-01-08 13:35         ` Wolfram Sang
2020-01-08 13:36           ` Laurent Pinchart
2019-12-31 16:13 ` [RFC PATCH 4/5] i2c: core: add simple caching to the 'alias' scanning Wolfram Sang
2020-01-07  9:59   ` Kieran Bingham
2020-01-21  9:22   ` Peter Rosin
2020-01-21  9:22     ` Peter Rosin
2019-12-31 16:14 ` [RFC PATCH 5/5] simple test case for the I2C alias functionality Wolfram Sang
2019-12-31 16:27 ` [RFC PATCH 0/5] i2c: implement mechanism to retrieve an alias device Wolfram Sang

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