linux-kernel - [PATCH] ARM: dts: vf610: use reset values for L2 cache latencies

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Message-Id: <1448935166-2697-1-git-send-email-stefan@agner.ch>
Date:	Mon, 30 Nov 2015 17:59:26 -0800
From:	Stefan Agner <stefan@...er.ch>
To:	shawnguo@...nel.org, kernel@...gutronix.de
Cc:	robh+dt@...nel.org, pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux@....linux.org.uk, linux-arm-kernel@...ts.infradead.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Stefan Agner <stefan@...er.ch>
Subject: [PATCH] ARM: dts: vf610: use reset values for L2 cache latencies

Linux on Vybrid used several different L2 latencies so far, none
of them seem to be the right ones. According to the application note
AN4947 ("Understanding Vybrid Architecture"), the tag portion runs
on CPU clock and is inside the L2 cache controller, whereas the data
portion is stored in the external SRAM running on platform clock.
Hence it is likely that the correct value requires a higher data
latency then tag latency.

These are the values which have been used so far:
- The mainline values:
  arm,data-latency = <1 1 1>;
  arm,tag-latency = <2 2 2>;
  Those values have lead to problems on higher clocks. They look
  like a poor translation from the reset values (missing +1 offset
  and a mix up between tag/latency values).
- The Linux 3.0 (SoC vendor BSP) values (converted to DT notation):
  arm,data-latency = <4 2 3>
  arm,tag-latency = <4 2 3>
  The cache initialization function along with the value matches the
  i.MX6 code from the same kernel, so it seems that those values have
  just been copied.
- The Colibri values:
  arm,data-latency = <2 1 2>;
  arm,tag-latency = <3 2 3>;
  Those were a mix between the values of the Linux 3.0 based BSP and
  the mainline values above.
- The SoC Reset values (converted to DT notation):
  arm,data-latency = <3 3 3>;
  arm,tag-latency = <2 2 2>;

So far there is no official statement on what the correct values are.
See also the related Freescale community thread:
https://community.freescale.com/message/579785#579785

For now, the reset values seem to be the best bet. Remove all other
"bogus" values and use the reset value on vf610.dtsi level.

Signed-off-by: Stefan Agner <stefan@...er.ch>
---
Hi Shawn,

Any chance to get this into 4.4?

--
Stefan

 arch/arm/boot/dts/vf610-colibri.dtsi | 5 -----
 arch/arm/boot/dts/vf610.dtsi         | 2 +-
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/arch/arm/boot/dts/vf610-colibri.dtsi b/arch/arm/boot/dts/vf610-colibri.dtsi
index 19fe045..2d7eab7 100644
--- a/arch/arm/boot/dts/vf610-colibri.dtsi
+++ b/arch/arm/boot/dts/vf610-colibri.dtsi
@@ -18,8 +18,3 @@
 		reg = <0x80000000 0x10000000>;
 	};
 };
-
-&L2 {
-	arm,data-latency = <2 1 2>;
-	arm,tag-latency = <3 2 3>;
-};
diff --git a/arch/arm/boot/dts/vf610.dtsi b/arch/arm/boot/dts/vf610.dtsi
index 5f8eb1b..58bc6e4 100644
--- a/arch/arm/boot/dts/vf610.dtsi
+++ b/arch/arm/boot/dts/vf610.dtsi
@@ -19,7 +19,7 @@
 		reg = <0x40006000 0x1000>;
 		cache-unified;
 		cache-level = <2>;
-		arm,data-latency = <1 1 1>;
+		arm,data-latency = <3 3 3>;
 		arm,tag-latency = <2 2 2>;
 	};
 };
-- 
2.6.2

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