Re: [PATCH v10 1/3] scsi: ufs: Protect some contexts from unexpected clock scaling

[Stanley Chu <stanley.chu@mediatek.com>]

Hi Can,

On Tue, 2021-01-19 at 03:52 -0800, 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@codeaurora.org>
> ---
>  drivers/scsi/ufs/ufshcd.c | 83 +++++++++++++++++++++++++++++------------------
>  drivers/scsi/ufs/ufshcd.h |  6 +++-
>  2 files changed, 56 insertions(+), 33 deletions(-)
> 
> diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
> index 53fd59c..ba62d84 100644
> --- a/drivers/scsi/ufs/ufshcd.c
> +++ b/drivers/scsi/ufs/ufshcd.c
> @@ -1201,19 +1201,30 @@ 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 ||
> +	    ufshcd_wait_for_doorbell_clr(hba, DOORBELL_CLR_TOUT_US)) {
>  		ret = -EBUSY;
>  		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);
>  }
>  
>  /**
> @@ -1228,13 +1239,11 @@ 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) {
> @@ -1260,14 +1269,12 @@ 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;
>  }
>  
> @@ -1541,7 +1548,7 @@ 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,
> @@ -1555,7 +1562,7 @@ 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);
> @@ -1564,7 +1571,7 @@ 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);
> @@ -1902,8 +1909,6 @@ 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)
> @@ -1911,6 +1916,8 @@ 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);
>  }
> @@ -1975,7 +1982,7 @@ 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)
> @@ -5093,7 +5100,8 @@ static void __ufshcd_transfer_req_compl(struct ufs_hba *hba,
>  				update_scaling = true;
>  			}
>  		}
> -		if (ufshcd_is_clkscaling_supported(hba) && update_scaling)
> +		if (ufshcd_is_clkscaling_supported(hba) && update_scaling &&

> +		    hba->clk_scaling.active_reqs > 0)
Do we need to check hba->clk_scaling.active_reqs here?

if hba->clk_scaling.active_reqs is possibly decreased to negative value
here, then there may be something to be fixed?

Otherwise this patch looks good to me.

Thanks,
Stanley Chu

>  			hba->clk_scaling.active_reqs--;
>  	}
>  
> @@ -5759,18 +5767,24 @@ static void ufshcd_err_handling_prepare(struct ufs_hba *hba)
>  		ufshcd_vops_resume(hba, pm_op);
>  	} 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);
>  }
> @@ -7750,12 +7764,14 @@ 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);
> @@ -8672,11 +8688,14 @@ 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) {
> @@ -8773,8 +8792,6 @@ 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);
>  	/*
>  	 * Device hardware reset is required to exit DeepSleep. Also, for
> @@ -8798,7 +8815,10 @@ 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;
> @@ -8901,7 +8921,10 @@ 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 */
> @@ -8925,8 +8948,6 @@ 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;
> @@ -9153,8 +9174,6 @@ 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 85f9d0f..d553e46 100644
> --- a/drivers/scsi/ufs/ufshcd.h
> +++ b/drivers/scsi/ufs/ufshcd.h
> @@ -419,7 +419,10 @@ struct ufs_saved_pwr_info {
>   * @suspend_work: worker to suspend devfreq
>   * @resume_work: worker to resume devfreq
>   * @min_gear: lowest HS gear to scale down to
> - * @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
>   */
> @@ -434,6 +437,7 @@ struct ufs_clk_scaling {
>  	struct work_struct suspend_work;
>  	struct work_struct resume_work;
>  	u32 min_gear;
> +	bool is_enabled;
>  	bool is_allowed;
>  	bool is_busy_started;
>  	bool is_suspended;