linux-kernel - Re: [PATCH v5 00/10] clk: implement clock rate protection mechanism

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Date:   Tue, 19 Dec 2017 16:38:30 -0800
From:   Michael Turquette <mturquette@...libre.com>
To:     Jerome Brunet <jbrunet@...libre.com>,
        "Stephen Boyd" <sboyd@...eaurora.org>
Cc:     "Jerome Brunet" <jbrunet@...libre.com>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        "Russell King" <linux@...linux.org.uk>,
        "Linus Walleij" <linus.walleij@...aro.org>,
        "Quentin Schulz" <quentin.schulz@...e-electrons.com>,
        "Kevin Hilman" <khilman@...libre.com>,
        "Maxime Ripard" <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH v5 00/10] clk: implement clock rate protection mechanism

Quoting Jerome Brunet (2017-12-01 13:51:50)
> This Patchset is related the RFC [0] and the discussion around
> CLK_SET_RATE_GATE available here [1]
> 
> This patchset introduce clock protection to the CCF core. This can then
> be used for:
> 
> * Provide a way for a consumer to claim exclusivity over the rate control
>   of a provider. Some clock consumers require that a clock rate must not
>   deviate from its selected frequency. There can be several reasons for
>   this, not least of which is that some hardware may not be able to
>   handle or recover from a glitch caused by changing the clock rate while
>   the hardware is in operation. For such HW, The ability to get exclusive
>   control of a clock's rate, and release that exclusivity, could be seen
>   as a fundamental clock rate control primitive. The exclusivity is not
>   preemptible, so when claimed more than once, is rate is effectively
>   locked.
> 
> * Provide a similar functionality to providers themselves, fixing
>   CLK_SET_RATE_GATE flag (enforce clock gating along the tree). While
>   there might still be a few platforms relying the broken implementation,
>   tests done has shown this change to be pretty safe.

Applied to clk-protect-rate, with the exception that I did not apply
"clk: fix CLK_SET_RATE_GATE with clock rate protection" as it breaks
qcom clk code.

Stephen, do you plan to fix up the qcom clock code so that the
SET_RATE_GATE improvement can go in?

Thanks,
Mike

> 
> Changes since v4: [4]
>  - Fixup documentation comments
>  - Fix error on exclusive API when CCF is disabled
> 
> Changes since v3: [3]
>  - Reorder patches following Stephen comments
>  - Add before/after examples to the cosmetic change
>  - Remove loops around protection where possible
>  - Rename the API from "protect" to "exclusive" which decribe what the
>    code better
> 
> Changes since v2: [2]
>  - Fix issues reported by Adriana Reus (Thanks !)
>  - Dropped patch "clk: move CLK_SET_RATE_GATE protection from prepare
>    to enable". This was broken as the protect count, like the prepare_count
>    should only be accessed under the prepare_lock.
> 
> Changes since v1: [1]
>  - Check if the rate would actually change before continuing, and bail-out
>    early if not.
> 
> Changes since RFC: [0]
>  - s/clk_protect/clk_rate_protect
>  - Request rework around core_nolock function
>  - Add clk_set_rate_protect
>  - Reword clk_rate_protect and clk_unprotect documentation
>  - Add few comments to explain the code
>  - Add fixes for CLK_SET_RATE_GATE
> 
> This was tested with the audio use case mentioned in [1]
> 
> [0]: https://lkml.kernel.org/r/20170321183330.26722-1-jbrunet@baylibre.com
> [1]: https://lkml.kernel.org/r/148942423440.82235.17188153691656009029@resonance
> [2]: https://lkml.kernel.org/r/20170521215958.19743-1-jbrunet@baylibre.com
> [3]: https://lkml.kernel.org/r/20170612194438.12298-1-jbrunet@baylibre.com
> [4]: https://lkml.kernel.org/r/20170924200030.6227-1-jbrunet@baylibre.com
> 
> Jerome Brunet (10):
>   clk: fix incorrect usage of ENOSYS
>   clk: take the prepare lock out of clk_core_set_parent
>   clk: add clk_core_set_phase_nolock function
>   clk: rework calls to round and determine rate callbacks
>   clk: use round rate to bail out early in set_rate
>   clk: add clock protection mechanism to clk core
>   clk: cosmetic changes to clk_summary debugfs entry
>   clk: fix CLK_SET_RATE_GATE with clock rate protection
>   clk: add clk_rate_exclusive api
>   clk: fix set_rate_range when current rate is out of range
> 
>  drivers/clk/clk.c            | 509 +++++++++++++++++++++++++++++++++++++------
>  include/linux/clk-provider.h |   1 +
>  include/linux/clk.h          |  62 ++++++
>  3 files changed, 502 insertions(+), 70 deletions(-)
> 
> -- 
> 2.14.3
>