From: Marek Vasut <marex@denx.de>
To: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Cc: Maxime Coquelin <mcoquelin.stm32@gmail.com>,
Raphael GALLAIS-POU <raphael.gallais-pou@st.com>,
David Airlie <airlied@linux.ie>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
Yannick FERTRE - foss <yannick.fertre@foss.st.com>,
Philippe CORNU <philippe.cornu@st.com>,
"dri-devel@lists.freedesktop.org"
<dri-devel@lists.freedesktop.org>,
Alexandre TORGUE - foss <alexandre.torgue@foss.st.com>,
Yannick FERTRE <yannick.fertre@st.com>,
Philippe CORNU - foss <philippe.cornu@foss.st.com>,
Benjamin Gaignard <benjamin.gaignard@linaro.org>,
Stephen Boyd <swboyd@chromium.org>,
"linux-stm32@st-md-mailman.stormreply.com"
<linux-stm32@st-md-mailman.stormreply.com>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH] drm/stm: ltdc: improve pm_runtime to stop clocks
Date: Fri, 2 Jul 2021 20:07:34 +0200 [thread overview]
Message-ID: <5d65ca80-4f94-49e1-5de1-cf29e8231a6a@denx.de> (raw)
In-Reply-To: <3bb823e4-4724-7072-fe9f-7b8a355c8e50@foss.st.com>
On 7/2/21 11:23 AM, Raphael Gallais-Pou wrote:
> Hello Marek,
Hi,
> Sorry for the late answer.
No worries, take your time
> On 6/30/21 2:35 AM, Marek Vasut wrote:
>> On 6/29/21 1:58 PM, Raphael GALLAIS-POU - foss wrote:
>>
>> [...]
>>
>>> +++ b/drivers/gpu/drm/stm/ltdc.c
>>> @@ -425,10 +425,17 @@ static void ltdc_crtc_atomic_enable(struct
>>> drm_crtc *crtc,
>>> {
>>> struct ltdc_device *ldev = crtc_to_ltdc(crtc);
>>> struct drm_device *ddev = crtc->dev;
>>> + int ret;
>>> DRM_DEBUG_DRIVER("\n");
>>> - pm_runtime_get_sync(ddev->dev);
>>> + if (!pm_runtime_active(ddev->dev)) {
>>> + ret = pm_runtime_get_sync(ddev->dev);
>>
>> All these if (!pm_runtime_active()) then pm_runtime_get_sync() calls
>> look like workaround for some larger issue. Shouldn't the pm_runtime
>> do some refcounting on its own , so this shouldn't be needed ?
>
>
> This problem purely comes from the driver internals, so I don't think it
> is a workaround.
>
> Because of the "ltdc_crtc_mode_set_nofb" function which does not have
> any "symmetrical" call, such as enable/disable functions, there was two
> calls to pm_runtime_get_sync against one call to pm_runtime_put_sync.
>
> This instability resulted in the LTDC clocks being always enabled, even
> when the peripheral was disabled. This could be seen in the clk_summary
> as explained in the patch summary among other things.
>
> By doing so, we first check if the clocks are not already activated, and
> in that case we call pm_runtime_get_sync.
I just have to wonder, how come other drivers don't need these if
(!pm_runtime_active()) pm_runtime_get_sync() conditions. I think they
just get/put the runtime PM within a call itself, not across function
calls. Maybe that could be the right fix here too ?
next prev parent reply other threads:[~2021-07-02 18:07 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-06-29 11:58 [PATCH] drm/stm: ltdc: improve pm_runtime to stop clocks Raphael GALLAIS-POU - foss
2021-06-30 0:35 ` Marek Vasut
2021-07-02 9:23 ` Raphael Gallais-Pou
2021-07-02 18:07 ` Marek Vasut [this message]
2021-08-17 9:43 ` Raphael Gallais-Pou
2021-08-19 22:22 ` Marek Vasut
2021-07-06 15:21 ` yannick Fertre
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