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Subject[PATCH] ce4100: Add errata fixes for UART on CE4100
Date
From: Dirk Brandewie <dirk.brandewie@gmail.com>

This patch enables the UART on the CE4100. The UART has a couple of
issues that need to be worked around. First the UART is mostly PC
compatible except that it is clocked eight times faster than a
standard PC so the default configuration provided in
arch/x86/include/asm/serial.h needs to be overridden. Second the TX
interrupt may not be set correctly all the time. Lastly accessing the
UART via I/O space for early_prink() hangs the chip when the IOAPIC is
enabled.

A custom mem_serial_in() is provided to work around the TX interrupt
issue. The configuration issues are dealt with in the call back
registered with the 8250 driver via serial8250_set_isa_configurator()

Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>
---
arch/x86/platform/ce4100/ce4100.c | 92 +++++++++++++++++++++++++++++++++++-
1 files changed, 89 insertions(+), 3 deletions(-)
diff --git a/arch/x86/platform/ce4100/ce4100.c b/arch/x86/platform/ce4100/ce4100.c
index b8f1c48..d2c0d51 100644
--- a/arch/x86/platform/ce4100/ce4100.c
+++ b/arch/x86/platform/ce4100/ce4100.c
@@ -12,25 +12,111 @@
#include <linux/kernel.h>
#include <linux/irq.h>
#include <linux/module.h>
+#include <linux/serial_reg.h>
+#include <linux/serial_8250.h>

#include <asm/setup.h>
-
+#include <asm/io.h>

static int ce4100_i8042_detect(void)
{
return 0;
}

-static void __init sdv_arch_setup(void)
+static void __init sdv_find_smp_config(void)
{
+}
+
+#ifdef CONFIG_SERIAL_8250
+

+static unsigned int mem_serial_in(struct uart_port *p, int offset)
+{
+ offset = offset << p->regshift;
+ return readl(p->membase + offset);
}

+/*
+ * The UART Tx interrupts are not set under some conditions and therefore serial
+ * transmission hangs. This is a silicon issue and has not been root caused. The
+ * workaround for this silicon issue checks UART_LSR_THRE bit and UART_LSR_TEMT
+ * bit of LSR register in interrupt handler to see whether at least one of these
+ * two bits is set, if so then process the transmit request. If this workaround
+ * is not applied, then the serial transmission may hang. This workaround is for
+ * errata number 9 in Errata - B step.
+*/

-static void __init sdv_find_smp_config(void)
+static unsigned int ce4100_mem_serial_in(struct uart_port *p, int offset)
+{
+ unsigned int ret, ier, lsr;
+
+ if (offset == UART_IIR) {
+ offset = offset << p->regshift;
+ ret = readl(p->membase + offset);
+ if (ret & UART_IIR_NO_INT) {
+ /* see if the TX interrupt should have really set */
+ ier = mem_serial_in(p, UART_IER);
+ /* see if the UART's XMIT interrupt is enabled */
+ if (ier & UART_IER_THRI) {
+ lsr = mem_serial_in(p, UART_LSR);
+ /* now check to see if the UART should be
+ generating an interrupt (but isn't) */
+ if (lsr & (UART_LSR_THRE | UART_LSR_TEMT))
+ ret &= ~UART_IIR_NO_INT;
+ }
+ }
+ } else
+ ret = mem_serial_in(p, offset);
+ return ret;
+}
+
+static void ce4100_mem_serial_out(struct uart_port *p, int offset, int value)
+{
+ offset = offset << p->regshift;
+ writel(value, p->membase + offset);
+}
+
+static void ce4100_serial_fixup(int port, struct uart_port *up,
+ unsigned short *capabilites)
+{
+#ifdef CONFIG_EARLY_PRINTK
+ /*
+ * Over ride the legacy port configuration that comes from
+ * asm/serial.h. Using the ioport driver then switching to the
+ * PCI memmaped driver hangs the IOAPIC
+ */
+ if (up->iotype != UPIO_MEM32) {
+ up->uartclk = 14745600;
+ up->mapbase = 0xdffe0200;
+ set_fixmap_nocache(FIX_EARLYCON_MEM_BASE,
+ up->mapbase & PAGE_MASK);
+ up->membase =
+ (void __iomem *)__fix_to_virt(FIX_EARLYCON_MEM_BASE);
+ up->membase += up->mapbase & ~PAGE_MASK;
+ up->iotype = UPIO_MEM32;
+ up->regshift = 2;
+ }
+#endif
+ up->iobase = 0;
+ up->serial_in = ce4100_mem_serial_in;
+ up->serial_out = ce4100_mem_serial_out;
+
+ *capabilites |= (1 << 12);
+}
+
+static __init void sdv_serial_fixup(void)
{
+ serial8250_set_isa_configurator(ce4100_serial_fixup);
}

+#else
+static inline void sdv_serial_fixup(void);
+#endif
+
+static void __init sdv_arch_setup(void)
+{
+ sdv_serial_fixup();
+}

/*
* CE4100 specific x86_init function overrides and early setup
--
1.7.2.3


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