From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver Date: Fri, 24 Jan 2020 17:04:19 +0300 Message-ID: <075e476a-36bb-5fee-15bc-76af4474a797@gmail.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> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <264d3354-8a2e-ee12-44ae-aff69213d551-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Content-Language: en-US Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Jon Hunter , Sameer Pujar Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, lgirdwood-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, atalambedu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, tiwai-IBi9RG/b67k@public.gmane.org, viswanathl-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, sharadg-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, rlokhande-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, mkumard-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, dramesh-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org List-Id: linux-tegra@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.