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Linux x86_64; rv:102.0) Gecko/20100101 Firefox/102.0 Thunderbird/102.14.0 Subject: Re: [PATCH v7] mmc: sdhci-of-dwcmshc: Add runtime PM operations Content-Language: en-US To: Ulf Hansson , Liming Sun Cc: David Thompson , Shawn Lin , linux-mmc@vger.kernel.org, linux-kernel@vger.kernel.org References: <79137159a833c164ea8ea3f05d8d6d9537db2f42.1683747334.git.limings@nvidia.com> <20230808202319.191434-1-limings@nvidia.com> <16047c7a-5bd1-868c-e6eb-e5f415e77fdd@intel.com> From: Adrian Hunter Organization: Intel Finland Oy, Registered Address: PL 281, 00181 Helsinki, Business Identity Code: 0357606 - 4, Domiciled in Helsinki In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-mmc@vger.kernel.org On 10/08/23 19:34, Ulf Hansson wrote: > On Thu, 10 Aug 2023 at 14:44, Adrian Hunter wrote: >> >> On 10/08/23 13:21, Ulf Hansson wrote: >>> On Thu, 10 Aug 2023 at 10:13, Adrian Hunter wrote: >>>> >>>> On 8/08/23 23:23, Liming Sun wrote: >>>>> This commit implements the runtime PM operations to disable eMMC >>>>> card clock when idle. >>>>> >>>>> Reviewed-by: David Thompson >>>>> Signed-off-by: Liming Sun >>>>> --- >>>>> v6->v7: >>>>> - Address Ulf's comment; >>>>> v5->v6: >>>>> - Address Adrian's more comments and add coordination between >>>>> runtime PM and system PM; >>>>> v4->v5: >>>>> - Address Adrian's comment to move the pm_enable to the end to >>>>> avoid race; >>>>> v3->v4: >>>>> - Fix compiling reported by 'kernel test robot'; >>>>> v2->v3: >>>>> - Revise the commit message; >>>>> v1->v2: >>>>> Updates for comments from Ulf: >>>>> - Make the runtime PM logic generic for sdhci-of-dwcmshc; >>>>> v1: Initial version. >>>>> --- >>>>> drivers/mmc/host/sdhci-of-dwcmshc.c | 72 ++++++++++++++++++++++++++++- >>>>> 1 file changed, 70 insertions(+), 2 deletions(-) >>>>> >>>>> diff --git a/drivers/mmc/host/sdhci-of-dwcmshc.c b/drivers/mmc/host/sdhci-of-dwcmshc.c >>>>> index e68cd87998c8..c8e145031429 100644 >>>>> --- a/drivers/mmc/host/sdhci-of-dwcmshc.c >>>>> +++ b/drivers/mmc/host/sdhci-of-dwcmshc.c >>>>> @@ -15,6 +15,7 @@ >>>>> #include >>>>> #include >>>>> #include >>>>> +#include >>>>> #include >>>>> #include >>>>> >>>>> @@ -548,9 +549,13 @@ static int dwcmshc_probe(struct platform_device *pdev) >>>>> >>>>> host->mmc->caps |= MMC_CAP_WAIT_WHILE_BUSY; >>>>> >>>>> + pm_runtime_get_noresume(dev); >>>>> + pm_runtime_set_active(dev); >>>>> + pm_runtime_enable(dev); >>>>> + >>>>> err = sdhci_setup_host(host); >>>>> if (err) >>>>> - goto err_clk; >>>>> + goto err_rpm; >>>>> >>>>> if (rk_priv) >>>>> dwcmshc_rk35xx_postinit(host, priv); >>>>> @@ -559,10 +564,15 @@ static int dwcmshc_probe(struct platform_device *pdev) >>>>> if (err) >>>>> goto err_setup_host; >>>>> >>>>> + pm_runtime_put(dev); >>>>> + >>>>> return 0; >>>>> >>>>> err_setup_host: >>>>> sdhci_cleanup_host(host); >>>>> +err_rpm: >>>>> + pm_runtime_disable(dev); >>>>> + pm_runtime_put_noidle(dev); >>>>> err_clk: >>>>> clk_disable_unprepare(pltfm_host->clk); >>>>> clk_disable_unprepare(priv->bus_clk); >>>>> @@ -606,6 +616,12 @@ static int dwcmshc_suspend(struct device *dev) >>>>> if (ret) >>>>> return ret; >>>>> >>>>> + ret = pm_runtime_force_suspend(dev); >>>>> + if (ret) { >>>>> + sdhci_resume_host(host); >>>>> + return ret; >>>>> + } >>>> >>>> Since you are only using the runtime PM callbacks to turn off the card >>>> clock via SDHCI_CLOCK_CONTROL, pm_runtime_force_suspend() and >>>> pm_runtime_force_resume() are not needed at all. >>> >>> Right, it can be done without these too. >>> >>>> >>>> sdhci_suspend_host() does not care if SDHCI_CLOCK_CARD_EN is on or off. >>>> (And you are disabling pltfm_host->clk and priv->bus_clk, so presumably >>>> the result is no clock either way) >>>> >>>> sdhci_resume_host() does not restore state unless >>>> SDHCI_QUIRK2_HOST_OFF_CARD_ON is used, it just resets, so the internal clock >>>> SDHCI_CLOCK_INT_EN is off which is consistent with either runtime suspended >>>> or runtime resumed. >>> >>> Even if this may work, to me, it doesn't look like good practice for >>> how to use runtime PM in combination with system wide suspend/resume. >>> >>> The point is, sdhci_suspend|resume_host() may end up reading/writing >>> to sdhci registers - and we should *not* allow that (because it may >>> not always work), unless the sdhci controller has been runtime resumed >>> first, right? >> >> I am OK with drivers that just want to use runtime PM to turn off a >> functional clock. sdhci-tegra.c is also doing that although using the >> clock framework. > > Yes, I agree. At least this works for SoC specific drivers. > >> >> Certainly that approach assumes that the host controller's power state >> is not changed due to runtime PM. >> >> To ensure that the host controller is runtime resumed before calling >> sdhci_suspend_host(), we can just call pm_runtime_resume() I think. > > Yes, that was kind of what I proposed in the other thread as option 1) > (except for the replacement of pm_runtime_force_suspend|resume). > > Although, to be clear I would probably use pm_runtime_get_sync() > instead, to make sure the usage count is incremented too. In that case, a matching pm_runtime_put() is needed also at the end of the resume callback. > > I don't have a strong opinion here, but from an optimization point of > view I would at least consider what I proposed in option 2) (in the > other thread). The benefit is that it can allow us to potentially > avoid runtime resuming the device, during system suspend. > > Kind regards > Uffe