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[PATCH 4/7] Documentation: mtd: add a DT property to set the latency code of Spansion memory

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  [PATCH 4/7] Documentation: mtd: add a DT property to set the latency code of Spansion memory Cyrille Pitchen <cyrille.pitchen@atmel.com> - 2015-07-16 17:30 +0200
    Re: [PATCH 4/7] Documentation: mtd: add a DT property to set the latency code of Spansion memory Marek Vasut <marex@denx.de> - 2015-07-16 19:50 +0200

#1185965 — [PATCH 4/7] Documentation: mtd: add a DT property to set the latency code of Spansion memory

Both the SPI controller and the NOR flash memory need to agree on the
number of dummy cycles to use for Fast Read commands. For Spansion
memories, this number of dummy cycles is not given directly but through a
so called "latency code".
The latency code can be found into the memory datasheet and depends on the
SPI clock frequency, the Fast Read op code and the Single/Dual Data Rate
mode.

Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>
---
 .../devicetree/bindings/mtd/spansion-nor.txt       | 22 ++++++++++++++++++++++
 1 file changed, 22 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mtd/spansion-nor.txt

diff --git a/Documentation/devicetree/bindings/mtd/spansion-nor.txt b/Documentation/devicetree/bindings/mtd/spansion-nor.txt
new file mode 100644
index 000000000000..a55c62db0e6f
--- /dev/null
+++ b/Documentation/devicetree/bindings/mtd/spansion-nor.txt
@@ -0,0 +1,22 @@
+* Spansion NOR flash
+
+Optional properties:
+- spansion,latency-code : Only used when the "m25p,num-dummy-cycles" property is
+                          set. The Spansion latency code tells the NOR flash
+                          memory the number of dummy cycles to expect for each
+                          Fast Read command. The value to be used is provided by
+                          tables in the memory datasheet and depends on the SPI
+                          clock frequency and on the Single/Dual Data Rate mode.
+                          Then the value of "m25p,num-dummy-cycles" property
+                          should match the (Fast) Read command to be used for
+                          the chosen latency code.
+
+Example:
+
+	m25p80@0 {
+		compatible = "spansion,s25fl512s";
+		reg = <0>;
+		spi-max-frequency = <104000000>;
+		m25p,num-dummy-cycles = <8>;
+		spansion,latency-code = <2>;
+	};
-- 
1.8.2.2

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#1186143

On Thursday, July 16, 2015 at 05:27:51 PM, Cyrille Pitchen wrote:

Hi!

> Both the SPI controller and the NOR flash memory need to agree on the
> number of dummy cycles to use for Fast Read commands. For Spansion
> memories, this number of dummy cycles is not given directly but through a
> so called "latency code".
> The latency code can be found into the memory datasheet and depends on the
> SPI clock frequency, the Fast Read op code and the Single/Dual Data Rate
> mode.

Shouldn't you be able to derive the latency code from the above information,
which you already know then ?

Best regards,
Marek Vasut
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