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Groups > linux.kernel > #1433513

clk: Per controller locks (prepare & enable)

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Hi,


Problems:
1. Deadlocks on prepare lock in following scenario:
 - prepare_enable(some external clock through i2c)
   - i2c transfer
     - prepare_enable(i2c lock in SoC)
       - deadlock
See [1]. We implemented a workaround for this in few places like
10ff4c5239a1 ("i2c: exynos5: Fix possible ABBA deadlock by keeping I2C
clock prepared") and 34e81ad5f0b6 ("i2c: s3c2410: fix ABBA deadlock by
keeping clock prepared")

The goal would be to remove also this workaround.

2. The global prepare and enable locks are over-used. I didn't test the
congestion but intuition says that they could be improved.


Solution:
Make this locks per controller. This will directly solve problem #1
because these are different controllers. Still in-controller deadlock
could occur but we couldn't find a real case with it.


Question:
What do you think about it? I know that talk is cheap and code looks
better but before starting the work I would like to hear some
comments/opinions/ideas.


Best regards,
Krzysztof


[1]
http://www.krzk.eu/builders/boot-odroid-xu3-multi_v7/builds/34/steps/Boot%20odroid/logs/serial

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Thread

clk: Per controller locks (prepare & enable) Krzysztof Kozlowski <k.kozlowski@samsung.com> - 2016-06-29 09:30 +0200
  Re: clk: Per controller locks (prepare & enable) Javier Martinez Canillas <javier@osg.samsung.com> - 2016-06-30 18:30 +0200
    Re: clk: Per controller locks (prepare & enable) Javier Martinez Canillas <javier@osg.samsung.com> - 2016-07-04 17:20 +0200
      Re: clk: Per controller locks (prepare & enable) Javier Martinez Canillas <javier@osg.samsung.com> - 2016-07-04 17:30 +0200
      Re: clk: Per controller locks (prepare & enable) Krzysztof Kozlowski <k.kozlowski@samsung.com> - 2016-07-05 08:40 +0200
        Re: clk: Per controller locks (prepare & enable) Javier Martinez Canillas <javier@osg.samsung.com> - 2016-07-05 16:00 +0200
          Re: clk: Per controller locks (prepare & enable) Charles Keepax <ckeepax@opensource.wolfsonmicro.com> - 2016-07-07 14:10 +0200
            Re: clk: Per controller locks (prepare & enable) Krzysztof Kozlowski <k.kozlowski@samsung.com> - 2016-07-07 14:50 +0200
              Re: clk: Per controller locks (prepare & enable) Charles Keepax <ckeepax@opensource.wolfsonmicro.com> - 2016-07-07 18:10 +0200
    Re: clk: Per controller locks (prepare & enable) Krzysztof Kozlowski <k.kozlowski@samsung.com> - 2016-07-04 10:30 +0200

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