[S] Change in coreboot[master]: mb/siemens/mc_ehl2: Add dummy I2C devices to limit the I2C speed in OS

[Felix Held (Code Review)]

Felix Held has submitted this change. ( https://review.coreboot.org/c/coreboot/+/69306 )

Change subject: mb/siemens/mc_ehl2: Add dummy I2C devices to limit the I2C speed in OS
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mb/siemens/mc_ehl2: Add dummy I2C devices to limit the I2C speed in OS

In Linux, the I2C speed defaults to 400 kHz if there is no device
registered in ACPI which requests a different speed. Due to board
limitations (layout, bus load), 400 kHz are too fast which results in a
timing violation. Therefore, add a dummy I2C device to both used I2C
buses (I2C1 and I2C2) with a speed of 100 kHz. This will limit the bus
speed in Linux accordingly.

Change-Id: I507c53c9ec7f763cef18903609231b1a66ed98fa
Signed-off-by: Werner Zeh 
Reviewed-on: https://review.coreboot.org/c/coreboot/+/69306
Tested-by: build bot (Jenkins) 
Reviewed-by: Mario Scheithauer 
---
M src/mainboard/siemens/mc_ehl/variants/mc_ehl2/devicetree.cb
1 file changed, 34 insertions(+), 1 deletion(-)

Approvals:
  build bot (Jenkins): Verified
  Mario Scheithauer: Looks good to me, approved

diff --git a/src/mainboard/siemens/mc_ehl/variants/mc_ehl2/devicetree.cb b/src/mainboard/siemens/mc_ehl/variants/mc_ehl2/devicetree.cb
index 4109ec9..d5d1277 100644
--- a/src/mainboard/siemens/mc_ehl/variants/mc_ehl2/devicetree.cb
+++ b/src/mainboard/siemens/mc_ehl/variants/mc_ehl2/devicetree.cb
@@ -144,8 +144,21 @@
    			register "cap_charge" = "CHARGE_OFF"
    			device i2c 0x52 on end  # RTC RV3028-C7
    		end
+			# Add dummy I2C device to limit BUS speed to 100 kHz in OS
+			chip drivers/i2c/generic
+				register "hid" = ""PRP0001""
+				register "speed" = "I2C_SPEED_STANDARD"
+				device i2c 0x7f on end
+			end
    	end
-		device pci 15.2 on	end # I2C2
+		device pci 15.2 on	    # I2C2
+		# Add dummy I2C device to limit BUS speed to 100 kHz in OS
+			chip drivers/i2c/generic
+				register "hid" = ""PRP0001""
+				register "speed" = "I2C_SPEED_STANDARD"
+				device i2c 0x7f on end
+			end
+		end
    	device pci 15.3 on	end # I2C3

device pci 16.0 hidden	end # Management Engine Interface 1