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[79.139.233.37]) by smtp.googlemail.com with ESMTPSA id i13sm3094490ljg.89.2020.01.24.06.04.21 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 24 Jan 2020 06:04:22 -0800 (PST) Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver To: Jon Hunter , Sameer Pujar Cc: devicetree@vger.kernel.org, alsa-devel@alsa-project.org, lgirdwood@gmail.com, linux-kernel@vger.kernel.org, broonie@kernel.org, atalambedu@nvidia.com, tiwai@suse.com, viswanathl@nvidia.com, linux-tegra@vger.kernel.org, robh+dt@kernel.org, thierry.reding@gmail.com, sharadg@nvidia.com, 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> <1a84b393-938f-8bed-d08e-cc3bb6ed4844@gmail.com> <0fc814c2-0dc6-7741-b954-463381ff7fb9@nvidia.com> <9f73afdf-1e9a-cdbd-f972-a022d503ef51@nvidia.com> <264d3354-8a2e-ee12-44ae-aff69213d551@nvidia.com> From: Dmitry Osipenko Message-ID: <075e476a-36bb-5fee-15bc-76af4474a797@gmail.com> Date: Fri, 24 Jan 2020 17:04:19 +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: <264d3354-8a2e-ee12-44ae-aff69213d551@nvidia.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 24.01.2020 12:51, Jon Hunter пишет: > > On 24/01/2020 09:07, Jon Hunter wrote: >> >> On 23/01/2020 15:16, Dmitry Osipenko wrote: >>> 23.01.2020 12:22, Sameer Pujar пишет: >>>> >>>> >>>> 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 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); >>>> >>>> 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 >>>> if !RPM >>>> if (!pm_runtime_status_suspended(&pdev->dev)) // it is true always if !RPM >>>>         tegra210_i2s_runtime_suspend(&pdev->dev); >>> >>> Maybe this is fine for !RPM, but not really fine in a case of enabled >>> RPM. Device could be in resumed state after pm_runtime_disable() if it >>> wasn't suspended before the disabling. >> >> I don't see any problem with this for the !RPM case. > > Sorry I meant the RPM case. In other words, I don't see a problem for > neither the RPM case of the !RPM case. 1. Device shall be in RPM-suspended state at the time of driver's removal, unless there is a bug in the sound driver. Hence why do you need the dead code which doesn't bring any practical value? 2. Making changes underneath of RPM is simply error-prone. It may hit badly in the future once something will change in the RPM core.