From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH V1] i2c: busses: tegra: Add suspend-resume support Date: Thu, 6 Jun 2019 14:52:24 +0300 Message-ID: References: <1559195718-6693-1-git-send-email-bbiswas@nvidia.com> <9142282b-ab76-53a0-13ce-c43b8adc575f@nvidia.com> <4f14a218-332c-0263-c6c5-73a13b2446f0@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Bitan Biswas , Laxman Dewangan , Thierry Reding , Jonathan Hunter , linux-i2c@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org Cc: Shardar Mohammed , Sowjanya Komatineni , Mantravadi Karthik List-Id: linux-tegra@vger.kernel.org 06.06.2019 8:43, Bitan Biswas пишет: > > > On 5/31/19 5:43 AM, Dmitry Osipenko wrote: >> 31.05.2019 11:50, Bitan Biswas пишет: >>> >>> >>> On 5/30/19 4:27 AM, Dmitry Osipenko wrote: >>>> 30.05.2019 8:55, Bitan Biswas пишет: >>>>> Post suspend I2C registers have power on reset values. Before any >>>>> transfer initialize I2C registers to prevent I2C transfer timeout >>>>> and implement suspend and resume callbacks needed. Fix below errors >>>>> post suspend: >>>>> >>>>> 1) Tegra I2C transfer timeout during jetson tx2 resume: >>>>> >>>>> [   27.520613] pca953x 1-0074: calling pca953x_resume+0x0/0x1b0 @ >>>>> 2939, parent: i2c-1 >>>>> [   27.633623] tegra-i2c 3160000.i2c: i2c transfer timed out >>>>> [   27.639162] pca953x 1-0074: Unable to sync registers 0x3-0x5. -110 >>>>> [   27.645336] pca953x 1-0074: Failed to sync GPIO dir registers: -110 >>>>> [   27.651596] PM: dpm_run_callback(): pca953x_resume+0x0/0x1b0 >>>>> returns -110 >>>>> [   27.658375] pca953x 1-0074: pca953x_resume+0x0/0x1b0 returned -110 >>>>> after 127152 usecs >>>>> [   27.666194] PM: Device 1-0074 failed to resume: error -110 >>>>> >>>>> 2) Tegra I2C transfer timeout error on jetson Xavier post resume. >>>>> >>>>> Signed-off-by: Bitan Biswas >>>>> --- >>>>>    drivers/i2c/busses/i2c-tegra.c | 24 ++++++++++++++++++++++++ >>>>>    1 file changed, 24 insertions(+) >>>>> >>>>> diff --git a/drivers/i2c/busses/i2c-tegra.c >>>>> b/drivers/i2c/busses/i2c-tegra.c >>>>> index ebaa78d..f6a377f 100644 >>>>> --- a/drivers/i2c/busses/i2c-tegra.c >>>>> +++ b/drivers/i2c/busses/i2c-tegra.c >>>>> @@ -1687,9 +1687,33 @@ static int tegra_i2c_remove(struct >>>>> platform_device *pdev) >>>>>    } >>>>>      #ifdef CONFIG_PM_SLEEP >>>>> +static int tegra_i2c_suspend(struct device *dev) >>>>> +{ >>>>> +    struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev); >>>>> + >>>>> +    i2c_mark_adapter_suspended(&i2c_dev->adapter); >>>>> + >>>>> +    return 0; >>>>> +} >>>>> + >>>>> +static int tegra_i2c_resume(struct device *dev) >>>>> +{ >>>>> +    struct tegra_i2c_dev *i2c_dev = dev_get_drvdata(dev); >>>>> +    int ret; >>>>> + >>>>> +    i2c_lock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER); >>>>> +    ret = tegra_i2c_init(i2c_dev, false); >>>>> +    i2c_unlock_bus(&i2c_dev->adapter, I2C_LOCK_ROOT_ADAPTER); >>>> >>>> Why the locking is needed here? >>> >>> async resume could result in stress test issues if some client accesses >>> the i2c instance. This ensures the i2c instance is locked till the >>> initialization is complete. >> >> 1) This doesn't make much sense.. if client could access I2C during of >> tegra_i2c_init execution, then what stops it to perform the access >> before the lock is taken? > Client resumes will start after I2C instance resume because of driver > dependency. Since lock is the first call in i2c-tegra I believe I2C > calls of client will not start. You're incorrectly assuming that client can start resuming in the middle of the controller's resume process. I2C client's resume won't start until tegra_i2c_resume() is finished completely. That is because child drivers are resumed only after theirs parent is ready and this is guaranteed by the drivers core.