linux-samsung-soc.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
To: Sam Protsenko <semen.protsenko@linaro.org>
Cc: "Sylwester Nawrocki" <s.nawrocki@samsung.com>,
	"Paweł Chmiel" <pawel.mikolaj.chmiel@gmail.com>,
	"Chanwoo Choi" <cw00.choi@samsung.com>,
	"Tomasz Figa" <tomasz.figa@gmail.com>,
	"Rob Herring" <robh+dt@kernel.org>,
	"Stephen Boyd" <sboyd@kernel.org>,
	"Michael Turquette" <mturquette@baylibre.com>,
	"Ryu Euiyoul" <ryu.real@samsung.com>,
	"Tom Gall" <tom.gall@linaro.org>,
	"Sumit Semwal" <sumit.semwal@linaro.org>,
	"John Stultz" <john.stultz@linaro.org>,
	"Amit Pundir" <amit.pundir@linaro.org>,
	devicetree <devicetree@vger.kernel.org>,
	"linux-arm Mailing List" <linux-arm-kernel@lists.infradead.org>,
	linux-clk <linux-clk@vger.kernel.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Linux Samsung SOC" <linux-samsung-soc@vger.kernel.org>
Subject: Re: [PATCH 1/6] clk: samsung: Enable bus clock on init
Date: Wed, 6 Oct 2021 14:38:56 +0200	[thread overview]
Message-ID: <16ee07a1-afa9-b258-8836-e96de84551db@canonical.com> (raw)
In-Reply-To: <CAPLW+4kexaByx0nfy3q5g9XmrYdLav7E25h8qiO4Z_zmUVbRYQ@mail.gmail.com>

On 06/10/2021 12:46, Sam Protsenko wrote:
> On Wed, 15 Sept 2021 at 11:21, Krzysztof Kozlowski
> <krzysztof.kozlowski@canonical.com> wrote:
>>
>> On 14/09/2021 17:56, Sam Protsenko wrote:
>>> By default if bus clock has no users its "enable count" value is 0. It
>>> might be actually running if it's already enabled in bootloader, but
>>> then in some cases it can be disabled by mistake. For example, such case
>>> was observed when dw_mci_probe() enabled bus clock, then failed to do
>>> something and disabled that bus clock on error path. After that even
>>> attempt to read the 'clk_summary' file in DebugFS freezed forever, as
>>> CMU bus clock ended up being disabled and it wasn't possible to access
>>> CMU registers anymore.
>>>
>>> To avoid such cases, CMU driver must increment the ref count for that
>>> bus clock by running clk_prepare_enable(). There is already existing
>>> '.clk_name' field in struct samsung_cmu_info, exactly for that reason.
>>> It was added in commit 523d3de41f02 ("clk: samsung: exynos5433: Add
>>> support for runtime PM"). But the clock is actually enabled only in
>>> Exynos5433 clock driver. Let's mimic what is done there in generic
>>> samsung_cmu_register_one() function, so other drivers can benefit from
>>> that `.clk_name' field. As was described above, it might be helpful not
>>> only for PM reasons, but also to prevent possible erroneous clock gating
>>> on error paths.
>>>
>>> Another way to workaround that issue would be to use CLOCK_IS_CRITICAL
>>> flag for corresponding gate clocks. But that might be not very good
>>> design decision, as we might still want to disable that bus clock, e.g.
>>> on PM suspend.
>>>
>>> Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
>>> ---
>>>  drivers/clk/samsung/clk.c | 13 +++++++++++++
>>>  1 file changed, 13 insertions(+)
>>>
>>> diff --git a/drivers/clk/samsung/clk.c b/drivers/clk/samsung/clk.c
>>> index 1949ae7851b2..da65149fa502 100644
>>> --- a/drivers/clk/samsung/clk.c
>>> +++ b/drivers/clk/samsung/clk.c
>>> @@ -357,6 +357,19 @@ struct samsung_clk_provider * __init samsung_cmu_register_one(
>>>
>>>       ctx = samsung_clk_init(np, reg_base, cmu->nr_clk_ids);
>>>
>>> +     /* Keep bus clock running, so it's possible to access CMU registers */
>>> +     if (cmu->clk_name) {
>>> +             struct clk *bus_clk;
>>> +
>>> +             bus_clk = __clk_lookup(cmu->clk_name);
>>> +             if (bus_clk) {
>>> +                     clk_prepare_enable(bus_clk);
>>> +             } else {
>>> +                     pr_err("%s: could not find bus clock %s\n", __func__,
>>> +                            cmu->clk_name);
>>> +             }
>>> +     }
>>> +
>>
>> Solving this problem in generic way makes sense but your solution is
>> insufficient. You skipped suspend/resume paths and in such case you
>> should remove the Exynos5433-specific code.
>>
> 
> Keeping core bus clocks always running seems like a separate
> independent feature to me (not related to suspend/resume). It's
> mentioned in commit 523d3de41f02 ("clk: samsung: exynos5433: Add
> support for runtime PM") this way:
> 
>     "Also for each CMU there is one special parent clock, which has to
> be enabled all the time when any access to CMU registers is being
> done."
> 
> Why do you think suspend/resume paths have to be implemented along
> with it? Btw, I didn't add PM ops in clk-exynos850, as PM is not
> implemented on my board yet and I can't test it.

You can skip the runtime PM, so keep your patch almost like it is now
(in respect to Sylwester's comment about __clk_lookup). However now the
Exynos5433 will enable the clk_name twice: here and in
exynos5433_cmu_probe().

If you keep this approach, you need to remove duplicated part in
exynos5433_cmu_probe()...

> 
> If you are suggesting moving all stuff from exynos5433_cmu_probe()
> into samsung_cmu_register_one(), it would take passing platform_device
> there, and implementing all PM related operations. I guess it's not a
> super easy task, as it would require converting clk-exynos7 to
> platform_driver for instance, and re-testing everything on exynos5433
> and exynos7 boards (which I don't have).
> 
> What do you say if I pull that code to clk-exynos850.c instead for v2?
> Refactoring (merging stuff from exynos5433_cmu_probe() into
> samsung_cmu_register_one() ) can be done later, when I add PM ops into
> clk-exynos850.
> 
>> Best regards,
>> Krzysztof


Best regards,
Krzysztof

  reply	other threads:[~2021-10-06 12:39 UTC|newest]

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-14 15:56 [PATCH 0/6] clk: samsung: Introduce Exynos850 SoC clock driver Sam Protsenko
2021-09-14 15:56 ` [PATCH 1/6] clk: samsung: Enable bus clock on init Sam Protsenko
2021-09-15  8:21   ` Krzysztof Kozlowski
2021-10-06 10:46     ` Sam Protsenko
2021-10-06 12:38       ` Krzysztof Kozlowski [this message]
2021-10-06 13:29         ` Sam Protsenko
2021-10-08  6:50           ` Krzysztof Kozlowski
2021-09-15 12:51   ` Sylwester Nawrocki
2021-10-06 11:18     ` Sam Protsenko
2021-10-06 12:45       ` Krzysztof Kozlowski
2021-10-09 18:49       ` Sylwester Nawrocki
2021-09-14 15:56 ` [PATCH 2/6] clk: samsung: clk-pll: Implement pll0822x PLL type Sam Protsenko
2021-09-15  8:24   ` Krzysztof Kozlowski
2021-09-15 15:59   ` Chanwoo Choi
2021-09-14 15:56 ` [PATCH 3/6] clk: samsung: clk-pll: Implement pll0831x " Sam Protsenko
2021-09-15  8:26   ` Krzysztof Kozlowski
2021-09-15 16:11   ` Chanwoo Choi
2021-09-14 15:56 ` [PATCH 4/6] dt-bindings: clock: Add bindings definitions for Exynos850 CMU Sam Protsenko
2021-09-15  8:27   ` Krzysztof Kozlowski
2021-09-15 16:37   ` Chanwoo Choi
2021-10-05 10:28     ` Sam Protsenko
2021-10-06 10:49       ` Krzysztof Kozlowski
2021-10-06 13:31         ` Sam Protsenko
2021-09-21 21:10   ` Rob Herring
2021-09-14 15:56 ` [PATCH 5/6] dt-bindings: clock: Document Exynos850 CMU bindings Sam Protsenko
2021-09-14 21:35   ` Rob Herring
2021-09-15  8:28   ` Krzysztof Kozlowski
2021-10-05 11:48     ` Sam Protsenko
2021-09-15 16:47   ` Chanwoo Choi
2021-09-14 15:56 ` [PATCH 6/6] clk: samsung: Introduce Exynos850 clock driver Sam Protsenko
2021-09-15  8:59   ` Krzysztof Kozlowski
2021-10-05 11:29     ` Sam Protsenko
2021-10-06 12:50       ` Krzysztof Kozlowski
2021-09-15 13:07   ` Sylwester Nawrocki
2021-10-05 11:36     ` Sam Protsenko
2021-10-06 12:46       ` Krzysztof Kozlowski
2021-09-15 18:04   ` Chanwoo Choi
2021-09-15 22:00     ` Sam Protsenko

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=16ee07a1-afa9-b258-8836-e96de84551db@canonical.com \
    --to=krzysztof.kozlowski@canonical.com \
    --cc=amit.pundir@linaro.org \
    --cc=cw00.choi@samsung.com \
    --cc=devicetree@vger.kernel.org \
    --cc=john.stultz@linaro.org \
    --cc=linux-arm-kernel@lists.infradead.org \
    --cc=linux-clk@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-samsung-soc@vger.kernel.org \
    --cc=mturquette@baylibre.com \
    --cc=pawel.mikolaj.chmiel@gmail.com \
    --cc=robh+dt@kernel.org \
    --cc=ryu.real@samsung.com \
    --cc=s.nawrocki@samsung.com \
    --cc=sboyd@kernel.org \
    --cc=semen.protsenko@linaro.org \
    --cc=sumit.semwal@linaro.org \
    --cc=tom.gall@linaro.org \
    --cc=tomasz.figa@gmail.com \
    --subject='Re: [PATCH 1/6] clk: samsung: Enable bus clock on init' \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).