From mboxrd@z Thu Jan 1 00:00:00 1970 From: Sameer Pujar Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver Date: Thu, 23 Jan 2020 14:52:14 +0530 Message-ID: <0fc814c2-0dc6-7741-b954-463381ff7fb9@nvidia.com> References: <1579530198-13431-1-git-send-email-spujar@nvidia.com> <1579530198-13431-5-git-send-email-spujar@nvidia.com> <0c571858-d72c-97c2-2d6a-ead6fdde06eb@nvidia.com> <444731da-c4cd-8578-a732-c803eef31ef0@gmail.com> <598fe377-5b95-d30a-eb64-89a645166d42@gmail.com> <3f51939d-cf4b-f69b-728a-7eb99bbae458@nvidia.com> <34ac1fd3-ae0f-07f2-555f-a55087a2c9dc@nvidia.com> <1a84b393-938f-8bed-d08e-cc3bb6ed4844@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8"; format=flowed Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1a84b393-938f-8bed-d08e-cc3bb6ed4844@gmail.com> Content-Language: en-GB Sender: linux-kernel-owner@vger.kernel.org To: Dmitry Osipenko , Jon Hunter , perex@perex.cz, tiwai@suse.com, robh+dt@kernel.org Cc: spujar@nvidia.com, devicetree@vger.kernel.org, alsa-devel@alsa-project.org, atalambedu@nvidia.com, linux-kernel@vger.kernel.org, lgirdwood@gmail.com, viswanathl@nvidia.com, sharadg@nvidia.com, broonie@kernel.org, thierry.reding@gmail.com, linux-tegra@vger.kernel.org, rlokhande@nvidia.com, mkumard@nvidia.com, dramesh@nvidia.com List-Id: linux-tegra@vger.kernel.org On 1/22/2020 9:57 PM, Dmitry Osipenko wrote: > External email: Use caution opening links or attachments > > > 22.01.2020 14:52, Jon Hunter =D0=BF=D0=B8=D1=88=D0=B5=D1=82: >> On 22/01/2020 07:16, Sameer Pujar wrote: >> >> ... >> >>>>>>>>> +static int tegra210_i2s_remove(struct platform_device *pdev) >>>>>>>>> +{ >>>>>>>>> + pm_runtime_disable(&pdev->dev); >>>>>>>>> + if (!pm_runtime_status_suspended(&pdev->dev)) >>>>>>>>> + tegra210_i2s_runtime_suspend(&pdev->dev); >>>>>>>> This breaks device's RPM refcounting if it was disabled in the act= ive >>>>>>>> state. This code should be removed. At most you could warn about t= he >>>>>>>> unxpected RPM state here, but it shouldn't be necessary. >>>>>>> I guess this was added for safety and explicit suspend keeps clock >>>>>>> disabled. >>>>>>> Not sure if ref-counting of the device matters when runtime PM is >>>>>>> disabled and device is removed. >>>>>>> I see few drivers using this way. >>>>>> It should matter (if I'm not missing something) because RPM should >>>>>> be in >>>>>> a wrecked state once you'll try to re-load the driver's module. Like= ly >>>>>> that those few other drivers are wrong. >>>>>> >>>>>> [snip] >>>>> Once the driver is re-loaded and RPM is enabled, I don't think it >>>>> would use >>>>> the same 'dev' and the corresponding ref count. Doesn't it use the ne= w >>>>> counters? >>>>> If RPM is not working for some reason, most likely it would be the ca= se >>>>> for other >>>>> devices. What best driver can do is probably do a force suspend durin= g >>>>> removal if >>>>> already not done. I would prefer to keep, since multiple drivers stil= l >>>>> have it, >>>>> unless there is a real harm in doing so. >>>> I took a closer look and looks like the counter actually should be >>>> reset. Still I don't think that it's a good practice to make changes >>>> underneath of RPM, it may strike back. >>> If RPM is broken, it probably would have been caught during device usag= e. >>> I will remove explicit suspend here if no any concerns from other folks= . >>> Thanks. >> I recall that this was the preferred way of doing this from the RPM >> folks. Tegra30 I2S driver does the same and Stephen had pointed me to >> this as a reference. >> I believe that this is meant to ensure that the >> device is always powered-off regardless of it RPM is enabled or not and >> what the current state is. > Yes, it was kinda actual for the case of unavailable RPM. > Anyways, /I think/ variant like this should have been more preferred: > > if (!pm_runtime_enabled(&pdev->dev)) > tegra210_i2s_runtime_suspend(&pdev->dev); > else > pm_runtime_disable(&pdev->dev); I think it looks to be similar to what is there already. pm_runtime_disable(&pdev->dev); // it would turn out to be a dummy call=20 if !RPM if (!pm_runtime_status_suspended(&pdev->dev)) // it is true always if !RPM =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 tegra210_i2s_runtime_suspend(&p= dev->dev); >> Now for Tegra210 (or actually 64-bit Tegra) RPM is always enabled and so >> we don't need to worry about the !RPM case. However, I still don't see >> the harm in this. > There is no real harm today, but: > > 1. I'd prefer to be very careful with RPM in general, based on > previous experience. > > 2. It should be a bug if device isn't RPM-suspended during > of driver's removal. Thus the real problem needs to be fixed > rather than worked around.