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Date:   Fri, 15 Sep 2023 22:02:36 +0800
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Subject: Re: [RFT PATCH 2/6] drm: Call drm_atomic_helper_shutdown() at
 shutdown time for misc drivers
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To:     Doug Anderson <dianders@chromium.org>
Cc:     dri-devel@lists.freedesktop.org,
        Maxime Ripard <mripard@kernel.org>, airlied@gmail.com,
        airlied@redhat.com, alain.volmat@foss.st.com,
        alexander.deucher@amd.com, alexandre.belloni@bootlin.com,
        alison.wang@nxp.com, bbrezillon@kernel.org,
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        jernej.skrabec@gmail.com, jfalempe@redhat.com, jstultz@google.com,
        kong.kongxinwei@hisilicon.com, kraxel@redhat.com,
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        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
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        nicolas.ferre@microchip.com, paul.kocialkowski@bootlin.com,
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        virtualization@lists.linux-foundation.org, wens@csie.org,
        xinliang.liu@linaro.org, yongqin.liu@linaro.org, zackr@vmware.com
References: <20230901234015.566018-1-dianders@chromium.org>
 <20230901163944.RFT.2.I9115e5d094a43e687978b0699cc1fe9f2a3452ea@changeid>
 <e7d855b6-327e-8c0c-5913-75bba9b6cfcd@loongson.cn>
 <CAD=FV=XF65otS2S+6sg6qga6Le3xb1f5GC6R6qpf27zx49DQ6w@mail.gmail.com>
From:   suijingfeng <suijingfeng@loongson.cn>
In-Reply-To: <CAD=FV=XF65otS2S+6sg6qga6Le3xb1f5GC6R6qpf27zx49DQ6w@mail.gmail.com>
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Hi,


On 2023/9/15 21:44, Doug Anderson wrote:
> Hi,
>
> On Fri, Sep 15, 2023 at 2:11 AM suijingfeng <suijingfeng@loongson.cn> wrote:
>> Hi,
>>
>>
>> On 2023/9/2 07:39, Douglas Anderson wrote:
>>> Based on grepping through the source code these drivers appear to be
>>> missing a call to drm_atomic_helper_shutdown() at system shutdown
>>> time. Among other things, this means that if a panel is in use that it
>>> won't be cleanly powered off at system shutdown time.
>>>
>>> The fact that we should call drm_atomic_helper_shutdown() in the case
>>> of OS shutdown/restart comes straight out of the kernel doc "driver
>>> instance overview" in drm_drv.c.
>>>
>>> All of the drivers in this patch were fairly straightforward to fix
>>> since they already had a call to drm_atomic_helper_shutdown() at
>>> remove/unbind time but were just lacking one at system shutdown. The
>>> only hitch is that some of these drivers use the component model to
>>> register/unregister their DRM devices. The shutdown callback is part
>>> of the original device. The typical solution here, based on how other
>>> DRM drivers do this, is to keep track of whether the device is bound
>>> based on drvdata. In most cases the drvdata is the drm_device, so we
>>> can just make sure it is NULL when the device is not bound. In some
>>> drivers, this required minor code changes. To make things simpler,
>>> drm_atomic_helper_shutdown() has been modified to consider a NULL
>>> drm_device as a noop in the patch ("drm/atomic-helper:
>>> drm_atomic_helper_shutdown(NULL) should be a noop").
>>>
>>> Suggested-by: Maxime Ripard <mripard@kernel.org>
>>> Signed-off-by: Douglas Anderson <dianders@chromium.org>
>>> ---
>>
>> I have just tested the whole series, thanks for the patch. For drm/loongson only:
>>
>>
>> Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
>> Tested-by: Sui Jingfeng <suijingfeng@loongson.cn>
> Thanks!
>
>
>> By the way, I add 'pr_info("lsdc_pci_shutdown\n");' into the lsdc_pci_shutdown() function,
>> And seeing that lsdc_pci_shutdown() will be called when reboot and shutdown the machine.
>> I did not witness something weird happen at present. As you have said, this is useful for
>> drm panels drivers. But for the rest(drm/hibmc, drm/ast, drm/mgag200 and drm/loongson etc)
>> drivers, you didn't mention what's the benefit for those drivers.
> I didn't mention it because I have no idea! I presume that for
> non-drm_panel use cases it's not a huge deal, otherwise it wouldn't
> have been missing from so many drivers. Thus, my "one sentence" reason
> for the non-drm_panel case is just "we should do this because the
> documentation of the API says we should", which is already in the
> commit message. ;-)
>

OK, this sound fine.

> If you have a specific other benefit you'd like me to list then I'm happy to.

You should think about the answer of this question yourself.
But I will not object if you can't find one. OK. :-)

>
>> Probably, you can
>> mention it with at least one sentence at the next version. I also prefer to alter the
>> lsdc_pci_shutdown() function as the following pattern:
>>
>>
>> static void lsdc_pci_shutdown(struct pci_dev *pdev)
>> {
>>
>>       struct drm_device *ddev = pci_get_drvdata(pdev);
>>
>>       drm_atomic_helper_shutdown(ddev);
>> }
> I was hoping to land this patch without spinning it unless there's a
> good reason. How strongly do you feel about needing to change the
> above?


Not very strong, this version looks just fine.
I will not object if you keep it as is.
But I will also hear what the others reviewers say.
Thanks for the patch.

>
> -Doug