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From: Kirill Kapranov <>
To: Mark Brown <>
Cc: Geert Uytterhoeven <>,,,
Subject: Re: [PATCH -next] spi: Fix double IDR allocation with DT aliases
Date: Sat, 25 Aug 2018 20:54:53 +0300	[thread overview]
Message-ID: <> (raw)
In-Reply-To: <>

> 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].

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.



  reply	other threads:[~2018-08-25 17:55 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 [this message]
2018-08-26 13:24       ` Mark Brown
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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