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Date:   Thu, 31 Dec 2020 12:39:01 +0800
From:   Can Guo <cang@...eaurora.org>
To:     asutoshd@...eaurora.org, nguyenb@...eaurora.org,
        hongwus@...eaurora.org, ziqichen@...eaurora.org,
        rnayak@...eaurora.org, linux-scsi@...r.kernel.org,
        kernel-team@...roid.com, saravanak@...gle.com, salyzyn@...gle.com,
        cang@...eaurora.org
Cc:     Alim Akhtar <alim.akhtar@...sung.com>,
        Avri Altman <avri.altman@....com>,
        "James E.J. Bottomley" <jejb@...ux.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        Stanley Chu <stanley.chu@...iatek.com>,
        Bean Huo <beanhuo@...ron.com>,
        Bart Van Assche <bvanassche@....org>,
        Satya Tangirala <satyat@...gle.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 1/3] scsi: ufs: Protect some contexts from unexpected
 clock scaling

Hi Stanley,

I slightly updated this change, because I found that in 
ufshcd_devfreq_scale(),
in order to call ufshcd_wb_ctrl(), clk_scale_lock write sem is released 
once,
which breaks the assumption that clk_scale_lock wraps the entire func. 
So,
in ufshcd_devfreq_scale(), I changed the up_write() to downgrade_write() 
so that
the clk_scale_lock does not have to be released.

Thus, I removed your reviewed-by tag. It would be very helpful if you 
can review
it one more time. Thanks.

Happy new year!!!

Regards,
Can Guo.

On 2020-12-30 19:29, Can Guo wrote:
> In contexts like suspend, shutdown and error handling, we need to 
> suspend
> devfreq to make sure these contexts won't be disturbed by clock 
> scaling.
> However, suspending devfreq is not enough since users can still trigger 
> a
> clock scaling by manipulating the devfreq sysfs nodes like min/max_freq 
> and
> governor even after devfreq is suspended. Moreover, mere suspending 
> devfreq
> cannot synchroinze a clock scaling which has already been invoked 
> through
> these sysfs nodes. Add one more flag in struct clk_scaling and wrap the
> entire func ufshcd_devfreq_scale() with the clk_scaling_lock, so that 
> we
> can use this flag and clk_scaling_lock to control and synchronize clock
> scaling invoked through devfreq sysfs nodes.
> 
> Signed-off-by: Can Guo <cang@...eaurora.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 87 
> ++++++++++++++++++++++++++++++-----------------
>  drivers/scsi/ufs/ufshcd.h |  6 +++-
>  2 files changed, 60 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 0c148fc..44cbee1 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1147,19 +1147,33 @@ static int ufshcd_clock_scaling_prepare(struct
> ufs_hba *hba)
>  	 */
>  	ufshcd_scsi_block_requests(hba);
>  	down_write(&hba->clk_scaling_lock);
> -	if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
> +
> +	if (!hba->clk_scaling.is_allowed)
> +		ret = -EAGAIN;
> +	else if (ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US))
>  		ret = -EBUSY;
> +
> +	if (ret) {
>  		up_write(&hba->clk_scaling_lock);
>  		ufshcd_scsi_unblock_requests(hba);
> +		goto out;
>  	}
> 
> +	/* let's not get into low power until clock scaling is completed */
> +	ufshcd_hold(hba, false);
> +
> +out:
>  	return ret;
>  }
> 
> -static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
> +static void ufshcd_clock_scaling_unprepare(struct ufs_hba *hba, bool 
> writelock)
>  {
> -	up_write(&hba->clk_scaling_lock);
> +	if (writelock)
> +		up_write(&hba->clk_scaling_lock);
> +	else
> +		up_read(&hba->clk_scaling_lock);
>  	ufshcd_scsi_unblock_requests(hba);
> +	ufshcd_release(hba);
>  }
> 
>  /**
> @@ -1174,13 +1188,11 @@ static void
> ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
>  static int ufshcd_devfreq_scale(struct ufs_hba *hba, bool scale_up)
>  {
>  	int ret = 0;
> -
> -	/* let's not get into low power until clock scaling is completed */
> -	ufshcd_hold(hba, false);
> +	bool is_writelock = true;
> 
>  	ret = ufshcd_clock_scaling_prepare(hba);
>  	if (ret)
> -		goto out;
> +		return ret;
> 
>  	/* scale down the gear before scaling down clocks */
>  	if (!scale_up) {
> @@ -1206,14 +1218,12 @@ static int ufshcd_devfreq_scale(struct ufs_hba
> *hba, bool scale_up)
>  	}
> 
>  	/* Enable Write Booster if we have scaled up else disable it */
> -	up_write(&hba->clk_scaling_lock);
> +	downgrade_write(&hba->clk_scaling_lock);
> +	is_writelock = false;
>  	ufshcd_wb_ctrl(hba, scale_up);
> -	down_write(&hba->clk_scaling_lock);
> 
>  out_unprepare:
> -	ufshcd_clock_scaling_unprepare(hba);
> -out:
> -	ufshcd_release(hba);
> +	ufshcd_clock_scaling_unprepare(hba, is_writelock);
>  	return ret;
>  }
> 
> @@ -1487,7 +1497,7 @@ static ssize_t
> ufshcd_clkscale_enable_show(struct device *dev,
>  {
>  	struct ufs_hba *hba = dev_get_drvdata(dev);
> 
> -	return snprintf(buf, PAGE_SIZE, "%d\n", hba->clk_scaling.is_allowed);
> +	return snprintf(buf, PAGE_SIZE, "%d\n", hba->clk_scaling.is_enabled);
>  }
> 
>  static ssize_t ufshcd_clkscale_enable_store(struct device *dev,
> @@ -1501,7 +1511,7 @@ static ssize_t
> ufshcd_clkscale_enable_store(struct device *dev,
>  		return -EINVAL;
> 
>  	value = !!value;
> -	if (value == hba->clk_scaling.is_allowed)
> +	if (value == hba->clk_scaling.is_enabled)
>  		goto out;
> 
>  	pm_runtime_get_sync(hba->dev);
> @@ -1510,7 +1520,7 @@ static ssize_t
> ufshcd_clkscale_enable_store(struct device *dev,
>  	cancel_work_sync(&hba->clk_scaling.suspend_work);
>  	cancel_work_sync(&hba->clk_scaling.resume_work);
> 
> -	hba->clk_scaling.is_allowed = value;
> +	hba->clk_scaling.is_enabled = value;
> 
>  	if (value) {
>  		ufshcd_resume_clkscaling(hba);
> @@ -1845,8 +1855,6 @@ static void ufshcd_init_clk_scaling(struct 
> ufs_hba *hba)
>  	snprintf(wq_name, sizeof(wq_name), "ufs_clkscaling_%d",
>  		 hba->host->host_no);
>  	hba->clk_scaling.workq = create_singlethread_workqueue(wq_name);
> -
> -	ufshcd_clkscaling_init_sysfs(hba);
>  }
> 
>  static void ufshcd_exit_clk_scaling(struct ufs_hba *hba)
> @@ -1854,6 +1862,8 @@ static void ufshcd_exit_clk_scaling(struct 
> ufs_hba *hba)
>  	if (!ufshcd_is_clkscaling_supported(hba))
>  		return;
> 
> +	if (hba->clk_scaling.enable_attr.attr.name)
> +		device_remove_file(hba->dev, &hba->clk_scaling.enable_attr);
>  	destroy_workqueue(hba->clk_scaling.workq);
>  	ufshcd_devfreq_remove(hba);
>  }
> @@ -1918,7 +1928,7 @@ static void ufshcd_clk_scaling_start_busy(struct
> ufs_hba *hba)
>  	if (!hba->clk_scaling.active_reqs++)
>  		queue_resume_work = true;
> 
> -	if (!hba->clk_scaling.is_allowed || hba->pm_op_in_progress)
> +	if (!hba->clk_scaling.is_enabled || hba->pm_op_in_progress)
>  		return;
> 
>  	if (queue_resume_work)
> @@ -4987,7 +4997,8 @@ static void __ufshcd_transfer_req_compl(struct
> ufs_hba *hba,
>  				complete(hba->dev_cmd.complete);
>  			}
>  		}
> -		if (ufshcd_is_clkscaling_supported(hba))
> +		if (ufshcd_is_clkscaling_supported(hba) &&
> +		    hba->clk_scaling.active_reqs > 0)
>  			hba->clk_scaling.active_reqs--;
>  	}
> 
> @@ -5650,18 +5661,25 @@ static void ufshcd_err_handling_prepare(struct
> ufs_hba *hba)
>  		ufshcd_vops_resume(hba, UFS_RUNTIME_PM);
>  	} else {
>  		ufshcd_hold(hba, false);
> -		if (hba->clk_scaling.is_allowed) {
> +		if (hba->clk_scaling.is_enabled) {
>  			cancel_work_sync(&hba->clk_scaling.suspend_work);
>  			cancel_work_sync(&hba->clk_scaling.resume_work);
>  			ufshcd_suspend_clkscaling(hba);
>  		}
>  	}
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = false;
> +	up_write(&hba->clk_scaling_lock);
>  }
> 
>  static void ufshcd_err_handling_unprepare(struct ufs_hba *hba)
>  {
>  	ufshcd_release(hba);
> -	if (hba->clk_scaling.is_allowed)
> +
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = true;
> +	up_write(&hba->clk_scaling_lock);
> +	if (hba->clk_scaling.is_enabled)
>  		ufshcd_resume_clkscaling(hba);
>  	pm_runtime_put(hba->dev);
>  }
> @@ -7620,12 +7638,14 @@ static int ufshcd_add_lus(struct ufs_hba *hba)
>  			sizeof(struct ufs_pa_layer_attr));
>  		hba->clk_scaling.saved_pwr_info.is_valid = true;
>  		if (!hba->devfreq) {
> +			hba->clk_scaling.is_allowed = true;
>  			ret = ufshcd_devfreq_init(hba);
>  			if (ret)
>  				goto out;
> -		}
> 
> -		hba->clk_scaling.is_allowed = true;
> +			hba->clk_scaling.is_enabled = true;
> +			ufshcd_clkscaling_init_sysfs(hba);
> +		}
>  	}
> 
>  	ufs_bsg_probe(hba);
> @@ -8491,11 +8511,14 @@ static int ufshcd_suspend(struct ufs_hba *hba,
> enum ufs_pm_op pm_op)
>  	ufshcd_hold(hba, false);
>  	hba->clk_gating.is_suspended = true;
> 
> -	if (hba->clk_scaling.is_allowed) {
> +	if (hba->clk_scaling.is_enabled) {
>  		cancel_work_sync(&hba->clk_scaling.suspend_work);
>  		cancel_work_sync(&hba->clk_scaling.resume_work);
>  		ufshcd_suspend_clkscaling(hba);
>  	}
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = false;
> +	up_write(&hba->clk_scaling_lock);
> 
>  	if (req_dev_pwr_mode == UFS_ACTIVE_PWR_MODE &&
>  			req_link_state == UIC_LINK_ACTIVE_STATE) {
> @@ -8592,8 +8615,6 @@ static int ufshcd_suspend(struct ufs_hba *hba,
> enum ufs_pm_op pm_op)
>  	goto out;
> 
>  set_link_active:
> -	if (hba->clk_scaling.is_allowed)
> -		ufshcd_resume_clkscaling(hba);
>  	ufshcd_vreg_set_hpm(hba);
>  	if (ufshcd_is_link_hibern8(hba) && !ufshcd_uic_hibern8_exit(hba))
>  		ufshcd_set_link_active(hba);
> @@ -8603,7 +8624,10 @@ static int ufshcd_suspend(struct ufs_hba *hba,
> enum ufs_pm_op pm_op)
>  	if (!ufshcd_set_dev_pwr_mode(hba, UFS_ACTIVE_PWR_MODE))
>  		ufshcd_disable_auto_bkops(hba);
>  enable_gating:
> -	if (hba->clk_scaling.is_allowed)
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = true;
> +	up_write(&hba->clk_scaling_lock);
> +	if (hba->clk_scaling.is_enabled)
>  		ufshcd_resume_clkscaling(hba);
>  	hba->clk_gating.is_suspended = false;
>  	hba->dev_info.b_rpm_dev_flush_capable = false;
> @@ -8701,7 +8725,10 @@ static int ufshcd_resume(struct ufs_hba *hba,
> enum ufs_pm_op pm_op)
> 
>  	hba->clk_gating.is_suspended = false;
> 
> -	if (hba->clk_scaling.is_allowed)
> +	down_write(&hba->clk_scaling_lock);
> +	hba->clk_scaling.is_allowed = true;
> +	up_write(&hba->clk_scaling_lock);
> +	if (hba->clk_scaling.is_enabled)
>  		ufshcd_resume_clkscaling(hba);
> 
>  	/* Enable Auto-Hibernate if configured */
> @@ -8725,8 +8752,6 @@ static int ufshcd_resume(struct ufs_hba *hba,
> enum ufs_pm_op pm_op)
>  	ufshcd_vreg_set_lpm(hba);
>  disable_irq_and_vops_clks:
>  	ufshcd_disable_irq(hba);
> -	if (hba->clk_scaling.is_allowed)
> -		ufshcd_suspend_clkscaling(hba);
>  	ufshcd_setup_clocks(hba, false);
>  	if (ufshcd_is_clkgating_allowed(hba)) {
>  		hba->clk_gating.state = CLKS_OFF;
> @@ -8944,8 +8969,6 @@ void ufshcd_remove(struct ufs_hba *hba)
> 
>  	ufshcd_exit_clk_scaling(hba);
>  	ufshcd_exit_clk_gating(hba);
> -	if (ufshcd_is_clkscaling_supported(hba))
> -		device_remove_file(hba->dev, &hba->clk_scaling.enable_attr);
>  	ufshcd_hba_exit(hba);
>  }
>  EXPORT_SYMBOL_GPL(ufshcd_remove);
> diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
> index e0f00a4..5737679 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -382,7 +382,10 @@ struct ufs_saved_pwr_info {
>   * @workq: workqueue to schedule devfreq suspend/resume work
>   * @suspend_work: worker to suspend devfreq
>   * @resume_work: worker to resume devfreq
> - * @is_allowed: tracks if scaling is currently allowed or not
> + * @is_enabled: tracks if scaling is currently enabled or not, 
> controlled by
> +		clkscale_enable sysfs node
> + * @is_allowed: tracks if scaling is currently allowed or not, used to 
> block
> +		clock scaling which is not invoked from devfreq governor
>   * @is_busy_started: tracks if busy period has started or not
>   * @is_suspended: tracks if devfreq is suspended or not
>   */
> @@ -396,6 +399,7 @@ struct ufs_clk_scaling {
>  	struct workqueue_struct *workq;
>  	struct work_struct suspend_work;
>  	struct work_struct resume_work;
> +	bool is_enabled;
>  	bool is_allowed;
>  	bool is_busy_started;
>  	bool is_suspended;

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