0022-scsi-ufs-Use-turbo-write-in-concert-with-DVFS.patch

From fbe7de2518a4143a4026c636d6b7b6179988905c Mon Sep 17 00:00:00 2001
From: Avri Altman <avri.altman@wdc.com>
Date: Wed, 3 Apr 2019 19:57:26 +0300
Subject: [PATCH 22/25] scsi: ufs: Use turbo-write in concert with DVFS
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

The DVFS governor, triggers a scaling action (calling its target()
callback) whenever it decide that a scale/up down is necessary.  It is
making those decisions based on the system load, which contains all
kinds of requests – not necessarily writes.  Therefore, theoretically,
we should not use those triggers simply as it is.  Similarly, we cannot
replicate this mechanism just to account for write requests as it comes
with a serious cost – the DVFS with its accompanying clock scaling is a
heavy weight sub-module, both in code as well as in performance.

Nevertheless, let us re-examine the option of using the clock scaling as
it is.  Looking at the read/write load options - we might have decide
differently on option 3:

	read	write	turbo-write
-----------------------------------
1 |	low  |	low   |	OFF
2 |	low  |	high  |	ON
3 |	high |	low   |	ON
4 |	high |	high  |	ON

However, the cost is negligible – so few writes will get a higher
priority than they should, which is merely a second order mistake.  The
upside is re-using the already existing clock scaling mechanism.  So on
high load, either one - read or write, enable turbo-write mode, and when
the load decreases – disable it.

Luckily, the scale_up Boolean in ufshcd_devfreq_target() is doing
exactly that.  We will use it to enable/disable turbo write, just before
it performs the clock scaling, so that we will have the device ready
before the host is tempering with the bus clocks.

Change-Id: Id7974ac5df8d74776e411589d45a943495f35ff0
Signed-off-by: Avri Altman <avri.altman@wdc.com>
---
 drivers/scsi/ufs/ufshcd.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index bceebb8..77739a3 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -2234,6 +2234,11 @@ static int ufshcd_devfreq_target(struct device *dev,
 	}
 	spin_unlock_irqrestore(hba->host->host_lock, irq_flags);
 
+	if (scale_up)
+		ufshcd_enable_turbo_write(hba);
+	else
+		ufshcd_disable_turbo_write(hba);
+
 	start = ktime_get();
 	ret = ufshcd_devfreq_scale(hba, scale_up);
 	trace_ufshcd_profile_clk_scaling(dev_name(hba->dev),
-- 
2.7.4