Re: [PATCH 1/2] scsi: ufs: Protect some contexts from unexpected clock scaling

From: Can Guo
Date: Thu Dec 10 2020 - 20:11:21 EST


On 2020-12-11 01:34, Bean Huo wrote:
Hi Can

On Wed, 2020-12-09 at 05:35 -0800, Can Guo wrote:


@@ -1160,6 +1166,7 @@ static void
ufshcd_clock_scaling_unprepare(struct ufs_hba *hba)
{
up_write(&hba->clk_scaling_lock);
ufshcd_scsi_unblock_requests(hba);
+ ufshcd_release(hba);
}

/**
@@ -1175,12 +1182,9 @@ 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);
-
ret = ufshcd_clock_scaling_prepare(hba);
if (ret)
- goto out;
+ return ret;

/* scale down the gear before scaling down clocks */
if (!scale_up) {
@@ -1212,8 +1216,6 @@ static int ufshcd_devfreq_scale(struct ufs_hba
*hba, bool scale_up)

out_unprepare:
ufshcd_clock_scaling_unprepare(hba);
-out:
- ufshcd_release(hba);
return ret;
}

I didn't understand why moving ufshcd_hold/ufshcd_release into
ufshcd_clock_scaling_prepare()/ufshcd_clock_scaling_unprepare().


Say you change devfreq's governor to performance after UFS host
has entered runtime suspend.

governor_store
devfreq_performance_handler
update_devfreq
devfreq_set_target
ufshcd_devfreq_target
ufshcd_devfreq_scale

When ufshcd_devfreq_scale() calls ufshcd_hold() when host is already
runtime suspended, guess what, NoC issues. So clk_scaling.is_allowed
should be checked first.

Regards,

Can Guo.



@@ -1294,15 +1296,8 @@ static int ufshcd_devfreq_target(struct device
*dev,
}
spin_unlock_irqrestore(hba->host->host_lock, irq_flags);

- pm_runtime_get_noresume(hba->dev);
- if (!pm_runtime_active(hba->dev)) {
- pm_runtime_put_noidle(hba->dev);
- ret = -EAGAIN;
- goto out;
- }
start = ktime_get();
ret = ufshcd_devfreq_scale(hba, scale_up);
- pm_runtime_put(hba->dev);


which branch are you working on? I didn't see this part codes in the
branch 5.11/scsi-queue and 5.11/scsi-staging.

Bean