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Index: sys/dev/uart/uart_dev_mu.c
===================================================================
--- sys/dev/uart/uart_dev_mu.c
+++ sys/dev/uart/uart_dev_mu.c
@@ -140,6 +140,7 @@
static void uart_mu_putc(struct uart_bas *bas, int);
static int uart_mu_rxready(struct uart_bas *bas);
static int uart_mu_getc(struct uart_bas *bas, struct mtx *);
+static int cpu_clock(void);
static struct uart_ops uart_mu_ops = {
.probe = uart_mu_probe,
@@ -157,12 +158,6 @@
return (0);
}
-/*
- * According to the docs, the cpu clock is locked to 250Mhz when
- * the micro-uart is used
- */
-#define CPU_CLOCK 250000000
-
static void
uart_mu_param(struct uart_bas *bas, int baudrate, int databits, int stopbits,
int parity)
@@ -188,15 +183,11 @@
line |= LCR_WLEN8;
break;
}
-
__uart_setreg(bas, AUX_MU_LCR_REG, line);
/* See 2.2.1 BCM2835-ARM-Peripherals baudrate */
if (baudrate != 0) {
- baud = CPU_CLOCK / (8 * baudrate);
- /* XXX
- * baud = cpu_clock() / (8 * baudrate);
- */
+ baud = cpu_clock() / (8 * baudrate);
__uart_setreg(bas, AUX_MU_BAUD_REG, ((uint32_t)(baud & 0xFFFF)));
}
@@ -252,7 +243,7 @@
*/
struct uart_mu_softc {
struct uart_softc bas;
- uint16_t aux_ier; /* Interrupt mask */
+ uint16_t aux_ier; /* Interrupt mask */
};
static int uart_mu_bus_attach(struct uart_softc *);
@@ -518,4 +509,40 @@
__uart_setreg(bas, AUX_MU_CNTL_REG, CNTL_RXENAB|CNTL_TXENAB);
__uart_setreg(bas, AUX_MU_IER_REG, psc->aux_ier);
uart_unlock(sc->sc_hwmtx);
+}
+
+/*
+ * From www.raspberripi.org/documentation/configuration/uart.md
+ *
+ * "The baud rate of the mini UART is linked to the core frequency of
+ * the VPU on the VC4 GPU. This means that, as the VPU frequency governor
+ * varies the core frequency, the baud rate of the mini UART also changes"
+ *
+ * Since this is rather unusable for a uart the core frequency is locked
+ * if this uart is enabled in the config. Unfortantely it is locked
+ * to 250Mhz on Rpi2 and Rpi3 but 500Mhz on Rpi4 so this driver needs
+ * to determine which is needed. This is one approach, another approach
+ * might be to query bcm2835_cpufreq.c directly.
+ */
+
+#define RPI2_AND_3_CORE_CLOCK 250000000
+#define RPI4_CORE_CLOCK 500000000
+
+static int
+cpu_clock(void)
+{
+ char compat[255];
+ ssize_t compatlen;
+ char *curstr;
+ phandle_t root;
+
+ root = OF_peer(0);
+ if (root == 0)
+ return (RPI2_AND_3_CORE_CLOCK);
+ compatlen = OF_getprop(root, "compatible", compat, sizeof(compat));
+ for (curstr = compat; curstr < compat + compatlen; curstr++) {
+ if (strncmp(curstr, "4-model", 7) == 0)
+ return (RPI4_CORE_CLOCK);
+ }
+ return (RPI2_AND_3_CORE_CLOCK);
}

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