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[79.139.233.37]) by smtp.googlemail.com with ESMTPSA id d20sm20510706ljg.95.2020.01.22.08.27.11 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 22 Jan 2020 08:27:12 -0800 (PST) Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver To: Jon Hunter , Sameer Pujar , perex@perex.cz, tiwai@suse.com, robh+dt@kernel.org Cc: 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 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> From: Dmitry Osipenko Message-ID: <1a84b393-938f-8bed-d08e-cc3bb6ed4844@gmail.com> Date: Wed, 22 Jan 2020 19:27:11 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <34ac1fd3-ae0f-07f2-555f-a55087a2c9dc@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: devicetree-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org 22.01.2020 14:52, Jon Hunter пишет: > > 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 active >>>>>>> state. This code should be removed. At most you could warn about the >>>>>>> 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. Likely >>>>> 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 new >>>> counters? >>>> If RPM is not working for some reason, most likely it would be the case >>>> for other >>>> devices. What best driver can do is probably do a force suspend during >>>> removal if >>>> already not done. I would prefer to keep, since multiple drivers still >>>> 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 usage. >> 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); > 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.