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From: Jerome Brunet <jbrunet@baylibre.com>
To: Michael Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@codeaurora.org>
Cc: linux-clk@vger.kernel.org, linux-kernel@vger.kernel.org,
	Russell King <linux@armlinux.org.uk>,
	Linus Walleij <linus.walleij@linaro.org>,
	Quentin Schulz <quentin.schulz@free-electrons.com>,
	Kevin Hilman <khilman@baylibre.com>,
	Maxime Ripard <maxime.ripard@free-electrons.com>
Subject: Re: [PATCH v5 00/10] clk: implement clock rate protection mechanism
Date: Thu, 24 May 2018 16:53:56 +0200	[thread overview]
Message-ID: <1527173636.2822.66.camel@baylibre.com> (raw)
In-Reply-To: <20180423182136.43156.94025@harbor.lan>

On Mon, 2018-04-23 at 11:21 -0700, Michael Turquette wrote:
> Quoting Jerome Brunet (2018-02-02 04:50:28)
> > On Thu, 2018-02-01 at 09:43 -0800, Stephen Boyd wrote:
> > > > > > 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?
> > > > > > 
> > > > > 
> > > > > I started working on it a while back. Let's see if I can finish
> > > > > it off this weekend.
> > > > > 
> > > > 
> > > > Hi Stephen,
> > > > 
> > > > Have you been able find something to fix the qcom code regarding this issue ?
> > > > 
> > > 
> > > This is what I have. I'm unhappy with a few things. First, I made
> > > a spinlock for each clk, which is overkill. Most likely, just a
> > > single spinlock is needed per clk-controller device. Second, I
> > > haven't finished off the branch/gate part, so gating/ungating of
> > > branches needs to be locked as well to prevent branches from
> > > turning on while rates change. And finally, the 'branches' list is
> > > duplicating a bunch of information about the child clks of an
> > > RCG, so it feels like we need a core framework API to enable and
> > > disable clks forcibly while remembering what is enabled/disabled
> > > or at least to walk the clk tree and call some function.
> > 
> > Looks similar to Mike's CCR idea ;)
> 
> Giving clk provider drivers more control over the clocks that they
> provide is a similar concept, but the ancient ccr series dealt almost
> exclusively with set_rate and set_parent ops. 
> 
> > 
> > > 
> > > The spinlock per clk-controller is duplicating the regmap lock we
> > > already have, so we may want a regmap API to grab the lock, and
> > > then another regmap API to do reads/writes without grabbing the
> > > lock, and then finally release the lock with a regmap unlock API.
> > 
> > There is 'regsequence' for multiple write in a burst, but that's only if you do
> > write only ... I suppose you are more in read/update/writeback mode, so it
> > probably does not help much.
> > 
> > Maybe we could extend regmap's regsequence, to do a sequence of
> > regmap_update_bits() ?
> > 
> > Another possibility could be to provide your own lock/unlock ops when
> > registering the regmap. With this, you might be able to supply your own spinlock
> > to regmap. This is already supported by regmap, would it help ?
> 
> Stephen, was there ever an update on your end? This patch has been
> dangling for a while and I thought it was time to ping on it.
> 
> Regards,
> Mike

Mike, Stephen,
The patch as been sitting on list for 6 months now and CLK_SET_RATE_GATE still
does not really do what it should, at least not completely.
How can we progress on this ?

As explained in this mail [0] from March, I think there is a fairly simple way
to deal with platforms relying on the broken implementation, such as qcom and
the mmci driver.

[0]: https://lkml.kernel.org/r/1522398050.3871.12.camel@baylibre.com

Regards
Jerome

> 
> > 
> > > This part is mostly an optimization, but it would be nice to have
> > > so that multiple writes could be done in sequence. This way, the
> > > RCG code could do the special locking sequence and the branch
> > > code could do the fire and forget single bit update.
> 
>  

      reply	other threads:[~2018-05-24 14:54 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-12-01 21:51 Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 01/10] clk: fix incorrect usage of ENOSYS Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 02/10] clk: take the prepare lock out of clk_core_set_parent Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 03/10] clk: add clk_core_set_phase_nolock function Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 04/10] clk: rework calls to round and determine rate callbacks Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 05/10] clk: use round rate to bail out early in set_rate Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 06/10] clk: add clock protection mechanism to clk core Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 07/10] clk: cosmetic changes to clk_summary debugfs entry Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 08/10] clk: fix CLK_SET_RATE_GATE with clock rate protection Jerome Brunet
2018-03-30  8:20   ` Jerome Brunet
2017-12-01 21:51 ` [PATCH v5 09/10] clk: add clk_rate_exclusive api Jerome Brunet
2017-12-01 21:52 ` [PATCH v5 10/10] clk: fix set_rate_range when current rate is out of range Jerome Brunet
2017-12-20  0:38 ` [PATCH v5 00/10] clk: implement clock rate protection mechanism Michael Turquette
2017-12-20 17:45   ` Jerome Brunet
2017-12-22  2:15   ` Stephen Boyd
2018-01-29  9:22     ` Jerome Brunet
2018-02-01 17:43       ` Stephen Boyd
2018-02-02 12:50         ` Jerome Brunet
2018-04-23 18:21           ` Michael Turquette
2018-05-24 14:53             ` Jerome Brunet [this message]

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