From: Wolfram Sang <wsa@the-dreams.de>
To: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
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 14:19:29 +0100 [thread overview]
Message-ID: <20200108131929.GA834@kunai> (raw)
In-Reply-To: <20200103001056.GJ4843@pendragon.ideasonboard.com>
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> > > As I said to Laurent, too, I think the risk that a bus is not fully
> > > described is higher than a device which does not respond to a read_byte.
> > > In both cases, we would wrongly use an address in use.
>
> I don't fully agree with this, I think we shouldn't impose a penalty on
> every user because some device trees don't fully describe the hardware.
I haven't decided yet. However, my general preference is that for a
generic OS like Linux, saftey comes first, then performance. If you have
a fully described DT, then the overhead will be 1 read_byte transaction
per requested alias at probe time. We could talk about using quick_read
to half the overhead. You could even patch it away, if it is too much
for $customer.
> I think we should, at the very least, skip the probe and rely on DT if
> DT explicitly states that all used addresses are listed. We discussed a
> property to report addresses used by devices not described in DT, if
> that property is listed I would prefer trusting DT.
Yeah, we discussed this property and I have no intentions of dropping
it. I haven't though of including it into this series, but it probably
makes sense. We don't have to define much anyhow, just state what
already exists, I guess.
From Documentation/devicetree/bindings/i2c/i2c-ocores.txt:
dummy@60 {
compatible = "dummy";
reg = <0x60>;
};
I think "dummy" is generic enough to be described in i2c.txt.
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next prev parent reply other threads:[~2020-01-08 13:19 UTC|newest]
Thread overview: 42+ 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
2020-01-08 13:38 ` Wolfram Sang
2020-01-08 13:22 ` Wolfram Sang
2020-01-08 13:19 ` Wolfram Sang [this message]
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
2020-01-07 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
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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