3 files changed, 149 insertions, 0 deletions
diff --git a/Documentation/tutorial/flashing_firmware/ext_standalone.md b/Documentation/tutorial/flashing_firmware/ext_standalone.md
index 3a676ce47c..1cb03e1cc1 100644
--- a/Documentation/tutorial/flashing_firmware/ext_standalone.md
+++ b/Documentation/tutorial/flashing_firmware/ext_standalone.md
@@ -19,5 +19,45 @@ It is possible to set the onboard flash on hold and use another flash chip.
 Connect all lines one-to-one, except /HOLD. Pull /HOLD of the soldered flash IC
 low, and /HOLD of your replacement flash IC high.
 
+### SPI header
+Some boards feature a pin header which is connected to the SPI bus. This can
+also be used to connect a secondary flash chip.
+
+#### HP boards
+Many HP desktop mainboards have a 2x8 or 2x10 block of header pins which
+can be used to connect a second flash chip. One pin is connected to the
+onboard flash's /CS pin, and another is connected to the chipset's /CS
+pin. Normally a jumper cap is placed between these pins, allowing the
+chipset to access the onboard flash. To use this header, remove this
+jumper and connect all lines except /CS one-to-one with the
+corresponding pin on the header. The secondary flash chip's /CS line
+should be connected to the chipset /CS pin on the header. By doing this
+the secondary SPI flash, rather than the onboard flash, will respond to
+accesses from the chipset.
+
+![][hp_spi_header_pinout]
+
+![][hp_spi_header_mainboard]
+
+Note that on boards where this header is unpopulated, a jumper resistor
+will be populated nearby which serves the purpose of the jumper cap. One
+end should have continuity with the /CS pin on the flash, and the other
+end should have continuity with the chipset /CS pin on the unpopulated
+header. It may also be possible to find this resistor through visual
+inspection of the traces on the /CS pins. This resistor should be
+desoldered if you wish to solder a pin header to the board and connect a
+secondary flash, otherwise the onboard flash will always respond to
+accesses.
+
+#### Other boards
+Other boards may have similar headers, but will likely use a different
+pinout than the ones explicitly mentioned here. Usually such a header
+will be located near the onboard SPI flash. If schematics are available,
+the pinout for the header will likely be found in it, but it could also
+be determined using a multimeter in continuity mode to map out the
+connections between the SPI flash and the header.
+
 
 [EM100Pro]: https://www.dediprog.com/product/EM100Pro
+[hp_spi_header_pinout]: hp_spi_header.svg
+[hp_spi_header_mainboard]: hp_spi_header_mb.jpg
diff --git a/Documentation/tutorial/flashing_firmware/hp_spi_header.svg b/Documentation/tutorial/flashing_firmware/hp_spi_header.svg
new file mode 100644
index 0000000000..c29a444604
--- /dev/null
+++ b/Documentation/tutorial/flashing_firmware/hp_spi_header.svg
@@ -0,0 +1,109 @@
+<?xml version="1.0" encoding="UTF-8" standalone="no"?>
+
+<svg
+   width="40.266247mm"
+   height="20.267391mm"
+   viewBox="0 0 40.266247 20.267391"
+   version="1.1"
+   id="svg5"
+   xmlns="http://www.w3.org/2000/svg"
+   xmlns:svg="http://www.w3.org/2000/svg">
+  <defs
+     id="defs2" />
+  <g
+     id="layer1"
+     transform="translate(0.1322915,0.1322915)">
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.264583"
+       d="M 0,0 C 0,6.6676027 0,13.335205 0,20.002808"
+       id="path500" />
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.264583"
+       d="m 0,20.002808 c 13.333889,0 26.667777,0 40.001666,0 0,-6.667603 0,-13.3352053 0,-20.002808 -6.665673,0 -13.331347,0 -19.99702,0 0,6.6676027 0,13.335205 0,20.002808"
+       id="path506" />
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.264583"
+       d="m 0,0 c 3.3327445,0 6.6654889,0 9.9982334,0 0,6.6676027 0,13.335205 0,20.002808"
+       id="path508" />
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.264583"
+       d="m 0,10.001404 c 13.333889,0 26.667777,0 40.001666,0"
+       id="path510" />
+    <path
+       style="fill:none;stroke:#000000;stroke-width:0.264583"
+       d="m 30.003154,0 c 0,6.6676027 0,13.335205 0,20.002808"
+       id="path512" />
+    <text
+       xml:space="preserve"
+       font-size="2.82222px"
+       style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal"
+       x="22.156124"
+       y="6.3107877"
+       id="text676"><tspan
+         x="22.156124"
+         y="6.3107877">VCC</tspan></text>
+    <text
+       xml:space="preserve"
+       font-size="2.82222px"
+       style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal"
+       x="31.972855"
+       y="6.3107877"
+       id="text730"><tspan
+         id="tspan728"
+         x="31.972855"
+         y="6.3107877">GND</tspan></text>
+    <text
+       xml:space="preserve"
+       font-size="2.82222px"
+       style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal"
+       x="32.398666"
+       y="16.285427"
+       id="text734"><tspan
+         id="tspan732"
+         x="32.398666"
+         y="16.285427">CLK</tspan></text>
+    <text
+       xml:space="preserve"
+       font-size="2.82222px"
+       style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal"
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+       y="16.285427"
+       id="text738"><tspan
+         id="tspan736"
+         x="22.770041"
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+    <text
+       xml:space="preserve"
+       font-size="2.82222px"
+       style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal"
+       x="13.605446"
+       y="16.286804"
+       id="text742"><tspan
+         id="tspan740"
+         x="13.605446"
+         y="16.286804">DI</tspan></text>
+    <text
+       xml:space="preserve"
+       font-size="2.82222px"
+       style="fill: #000000;text-anchor:start;font-family:sans-serif;font-style:normal;font-weight:normal"
+       x="2.5204566"
+       y="6.1998558"
+       id="text746"><tspan
+         id="tspan744"
+         x="2.5204566"
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+    <text
+       xml:space="preserve"
+       font-size="2.5px"
+       style="fill: #000000;text-anchor:middle;font-family:sans-serif;font-style:normal;font-weight:normal"
+       x="5.0321894"
+       y="14.500522"
+       id="text750"><tspan
+         id="tspan748"
+         x="5.0321894"
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+         x="5.0321894"
+         y="17.146358"
+         id="tspan752">chipset</tspan></text>
+  </g>
+</svg>
diff --git a/Documentation/tutorial/flashing_firmware/hp_spi_header_mb.jpg b/Documentation/tutorial/flashing_firmware/hp_spi_header_mb.jpg
new file mode 100644
index 0000000000..b9edd734b8
--- /dev/null
+++ b/Documentation/tutorial/flashing_firmware/hp_spi_header_mb.jpg