From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jon Hunter Subject: Re: [alsa-devel] [PATCH 4/9] ASoC: tegra: add Tegra210 based I2S driver Date: Wed, 22 Jan 2020 11:52:14 +0000 Message-ID: <34ac1fd3-ae0f-07f2-555f-a55087a2c9dc@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> Mime-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <3f51939d-cf4b-f69b-728a-7eb99bbae458-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org> Content-Language: en-US Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Sameer Pujar , Dmitry Osipenko , perex-/Fr2/VpizcU@public.gmane.org, tiwai-IBi9RG/b67k@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, alsa-devel-K7yf7f+aM1XWsZ/bQMPhNw@public.gmane.org, atalambedu-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, lgirdwood-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, viswanathl-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, sharadg-DDmLM1+adcrQT0dZR+AlfA@public.gmane.org, broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org, linux-tegra-u79uwXL29TY76Z2rM5mHXA@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 On 22/01/2020 07:16, Sameer Pujar wrote: ... >>>>>>> +static int tegra210_i2s_remove(struct platform_device *pdev) >>>>>>> +{ >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 pm_runtime_disable(&pdev->dev); >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0 if (!pm_runtime_status_suspended(&pdev->d= ev)) >>>>>>> +=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0= =C2=A0 tegra210_i2s_runtime_suspend(&pdev->dev); >>>>>> This breaks device's RPM refcounting if it was disabled in the activ= e >>>>>> 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. >=20 > 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. 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. Jon --=20 nvpublic