linux-kernel - [PATCH 8/8] ARM: dts: at91: sam9x60ek: Set sst26vf064b SPI NOR flash at its maximum frequency

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Date:   Thu, 17 Nov 2022 12:52:49 +0200
From:   Tudor Ambarus <tudor.ambarus@...rochip.com>
To:     <broonie@...nel.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <nicolas.ferre@...rochip.com>,
        <alexandre.belloni@...tlin.com>, <claudiu.beznea@...rochip.com>
CC:     <linux-spi@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-mtd@...ts.infradead.org>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>
Subject: [PATCH 8/8] ARM: dts: at91: sam9x60ek: Set sst26vf064b SPI NOR flash at its maximum frequency

sam9x60ek populates an sst26vf064b SPI NOR flash. Its maximum operating
frequency for 2.7-3.6V is 104 MHz. As the flash is operated at 3.3V,
increase its maximum supported frequency to 104MHz. The increasing of the
spi-max-frequency value requires the setting of the
"CE# Not Active Hold Time", thus set the spi-cs-setup-ns to a value of 7.

The sst26vf064b datasheet specifies just a minimum value for the
"CE# Not Active Hold Time" and it advertises it to 5 ns. There's no
maximum time specified. I determined experimentally that 5 ns for the
spi-cs-setup-ns is not enough when the flash is operated close to its
maximum frequency and tests showed that 7 ns is just fine, so set the
spi-cs-setup-ns dt property to 7.

With the increase of frequency the reads are now faster with ~33%.

Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
---
 arch/arm/boot/dts/at91-sam9x60ek.dts | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/arm/boot/dts/at91-sam9x60ek.dts b/arch/arm/boot/dts/at91-sam9x60ek.dts
index 4ba52ba11dc6..6cbb4e0d9938 100644
--- a/arch/arm/boot/dts/at91-sam9x60ek.dts
+++ b/arch/arm/boot/dts/at91-sam9x60ek.dts
@@ -612,7 +612,8 @@ flash@0 {
 		#size-cells = <1>;
 		compatible = "jedec,spi-nor";
 		reg = <0>;
-		spi-max-frequency = <80000000>;
+		spi-max-frequency = <104000000>;
+		spi-cs-setup-ns = /bits/ 16 <7>;
 		spi-tx-bus-width = <4>;
 		spi-rx-bus-width = <4>;
 		m25p,fast-read;
-- 
2.25.1