From: Fabrice Gasnier <fabrice.gasnier@st.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Lee Jones <lee.jones@linaro.org>,
Rob Herring <robh+dt@kernel.org>,
Alexandre Torgue <alexandre.torgue@st.com>,
Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Mark Rutland <mark.rutland@arm.com>,
Gabriel Fernandez <gabriel.fernandez@st.com>,
DTML <devicetree@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
<linux-stm32@st-md-mailman.stormreply.com>,
Linux ARM <linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH v2 2/3] mfd: syscon: Add optional clock support
Date: Wed, 16 Jan 2019 15:10:08 +0100 [thread overview]
Message-ID: <9e0ee154-a399-9bff-3beb-adfd9d6c6fee@st.com> (raw)
In-Reply-To: <CAK8P3a1MucNG86=bXwVVsasGBOLJ67kuRSpoeneF6M5aB6GmQA@mail.gmail.com>
On 1/16/19 1:14 PM, Arnd Bergmann wrote:
> (sorry for the late reply, I just realized that I had never sent out the
> mail after Lee asked me for a review last year and I had drafted
> my reply).
Hi Arnd,
Many thanks for reviewing, no worries :-)
>
> On Wed, Dec 12, 2018 at 9:48 AM Fabrice Gasnier <fabrice.gasnier@st.com> wrote:
>>
>> Some system control registers need to be clocked, so the registers can
>> be accessed. Add an optional clock and attach it to regmap.
>>
>> Signed-off-by: Fabrice Gasnier <fabrice.gasnier@st.com>
>
> This looks ok to me in principle, but I have one question: When we
> do a clk_get() and clk_prepare() as part of regmap_mmio_attach_clk(),
> does that change the behavior of syscon nodes that are otherwise
> unused?
I'm not sure I correctly understand this question. I don't think it will
change the behavior for "unused" nodes. These should remain unused with
this patch.
>
> I think we have a bunch of devices that started out as a syscon but
> then we added a proper driver for them, which would handle the
> clocks explicitly. Is it guaranteed that this will keep working (including
> shutting down the clocks when they are unused) if we have two drivers
> that call clk_get() on the same device node?
I'd expect nothing wrong happens when two drivers call clk_get() for the
same clock.
Are there some case where two drivers are bind (e.g. syscon driver +
another driver) for the same piece of hardware ?
The clk_prepare() is part of regmap_mmio_attach_clk(). It's called once
upon registration via of_syscon_register(). There is currently no mean
to unregister, e.g. something like "of_syscon_unregister" and so do
clk_unprepare via regmap_mmio_detach_clk().
Then point is clk_enable()/clk_disable() calls will be used in
regmap_mmio_read() and regmap_mmio_write(). These calls are balanced.
Then clock framework should correctly disable/gate the clock when
unused, based on the enable count.
Is this answering your question?
Thanks again,
Best regards,
Fabrice
>
> Arnd
>
next prev parent reply other threads:[~2019-01-16 14:10 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-12 8:48 [PATCH v2 0/3] mfd: syscon: Add optional clock support needed on stm32 Fabrice Gasnier
2018-12-12 8:48 ` [PATCH v2 1/3] dt-bindings: stm32: syscon: add clock support Fabrice Gasnier
2018-12-18 17:12 ` Rob Herring
2019-03-20 13:05 ` Lee Jones
2018-12-12 8:48 ` [PATCH v2 2/3] mfd: syscon: Add optional " Fabrice Gasnier
2019-01-16 12:14 ` Arnd Bergmann
2019-01-16 14:10 ` Fabrice Gasnier [this message]
2019-01-16 15:11 ` Arnd Bergmann
2019-01-28 13:20 ` Fabrice Gasnier
2019-02-11 16:32 ` Fabrice Gasnier
2019-02-18 12:54 ` Arnd Bergmann
2019-03-20 13:05 ` Lee Jones
2018-12-12 8:48 ` [PATCH v2 3/3] ARM: dts: stm32: Add clock on stm32mp157c syscfg Fabrice Gasnier
2019-03-26 11:24 ` Alexandre Torgue
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