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From: Mark Brown <>
To: Kirill Kapranov <>
Cc: Geert Uytterhoeven <>,,,
Subject: Re: [PATCH -next] spi: Fix double IDR allocation with DT aliases
Date: Sun, 26 Aug 2018 14:24:15 +0100	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

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On Sat, Aug 25, 2018 at 08:54:53PM +0300, Kirill Kapranov wrote:
> > For DT systems the dynamically allocated IDs start at the maximum
> > positive ID and work down so in practice it is vanishingly unlikely that
> > there will be a collision as idiomatic static DT IDs would be low
> > integers.
> Yes, this algorithm seems really bullet-proof. However, it isn't actually
> used now. The ID allocation algorithm using  atomic_dec_return call had been
> introduced 2006-01-08 as [1]. It was being used in the mainline kernel (with
> some improvements) up to 2017-08-16, when it has been replaced with the
> newer algorithm using Linux idr, accordingly [2].

Please include human readable descriptions of things like commits and
issues being discussed in e-mail in your mails, this makes them much
easier for humans to read especially when they have no internet access.
I do frequently catch up on my mail on flights or while otherwise
travelling so this is even more pressing for me than just being about
making things a bit easier to read.

> Since idr_alloc call works incrementally, the situation of a 'fixed' ID
> squatting by a driver with 'dynamic ID' seems more than possible.
> Therefore it would be justified to use a hardcoded constant
> SPI_DYN_FIRST_BUS_NUM (that was introduced in [2] and eliminated in [3]),
> but with a sufficiently greater value of the constant.

Right, that clearly wasn't an intended effect, though - should be using
the max of the big constant and the maximum static ID.

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  reply	other threads:[~2018-08-26 13:24 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-21  9:53 [PATCH -next] spi: Fix double IDR allocation with DT aliases Geert Uytterhoeven
2018-08-21 13:40 ` Greg KH
2018-08-21 17:42   ` Geert Uytterhoeven
2018-08-22 17:51 ` Kirill Kapranov
2018-08-23 10:21   ` Mark Brown
2018-08-25 17:54     ` Kirill Kapranov
2018-08-26 13:24       ` Mark Brown [this message]
2018-08-28 19:47         ` Kirill kapranov
2018-08-27 14:13 ` Fabio Estevam
2018-08-28 20:58 ` Applied "spi: Fix double IDR allocation with DT aliases" to the spi tree Mark Brown

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