From be3df1c40e4623ad40bcd0d42a9d5e39354c4dd0 Mon Sep 17 00:00:00 2001
From: Thomas Maier <contact@thomas-maier.net>
Date: Sat, 27 Nov 2021 13:54:30 +0100
Subject: [PATCH] Fix incorrect core_freq for Raspberry Pi 4, Raspberry Pi 400
 and CM4

Compare https://github.com/raspberrypi/documentation/blob/develop/documentation/asciidoc/computers/config_txt/overclocking.adoc. Unfortunately i found no easy way to read 'core_freq'. This would be great, since the value is "wrong" for most of the RPi revisions.
---
 spi.go | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/spi.go b/spi.go
index 69ebc15..7a5954e 100644
--- a/spi.go
+++ b/spi.go
@@ -61,8 +61,11 @@ func SpiEnd(dev SpiDev) {
 // Param speed may be as big as 125MHz in theory, but
 // only values up to 31.25MHz are considered relayable.
 func SpiSpeed(speed int) {
-	const baseFreq = 250 * 1000000
-	cdiv := uint32(baseFreq / speed)
+	coreFreq := 250 * 1000000
+	if isBCM2711() {
+		coreFreq = 550 * 1000000
+	}
+	cdiv := uint32(coreFreq / speed)
 	setSpiDiv(cdiv)
 }