Add buffer_to/from_fifo32(_prefix) helpers

Many peripheral drivers across different SoCs regularly face the same
task of piping a transfer buffer into (or reading it out of) a 32-bit
FIFO register. Sometimes it's just one register, sometimes a whole array
of registers. Sometimes you actually transfer 4 bytes per register
read/write, sometimes only 2 (or even 1). Sometimes writes need to be
prefixed with one or two command bytes which makes the actual payload
buffer "misaligned" in relation to the FIFO and requires a bunch of
tricky bit packing logic to get right. Most of the times transfer
lengths are not guaranteed to be divisible by 4, which also requires a
bunch of logic to treat the potential unaligned end of the transfer
correctly.

We have a dozen different implementations of this same pattern across
coreboot. This patch introduces a new family of helper functions that
aims to solve all these use cases once and for all (*fingers crossed*).

Change-Id: Ia71f66c1cee530afa4c77c46a838b4de646ffcfb
Signed-off-by: Julius Werner <jwerner@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/34850
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

src/device/mmio.c

@@ -0,0 +1,55 @@
+/*
+ * This file is part of the coreboot project.
+ *
+ * Copyright 2019 Google LLC
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; version 2 of the License.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ */
+
+#include <assert.h>
+#include <device/mmio.h>
+
+/* Helper functions for various MMIO access patterns. */
+
+void buffer_from_fifo32(void *buffer, size_t size, void *fifo,
+			int fifo_stride, int fifo_width)
+{
+	u8 *p = buffer;
+	int i, j;
+
+	assert(fifo_width > 0 && fifo_width <= sizeof(u32) &&
+	       fifo_stride % sizeof(u32) == 0);
+
+	for (i = 0; i < size; i += fifo_width, fifo += fifo_stride) {
+		u32 val = read32(fifo);
+		for (j = 0; j < MIN(size - i, fifo_width); j++)
+			*p++ = (u8)(val >> (j * 8));
+	}
+}
+
+void buffer_to_fifo32_prefix(void *buffer, u32 prefix, int prefsz, size_t size,
+			     void *fifo, int fifo_stride, int fifo_width)
+{
+	u8 *p = buffer;
+	int i, j = prefsz;
+
+	assert(fifo_width > 0 && fifo_width <= sizeof(u32) &&
+	       fifo_stride % sizeof(u32) == 0 && prefsz <= fifo_width);
+
+	uint32_t val = prefix;
+	for (i = 0; i < size; i += fifo_width, fifo += fifo_stride) {
+		for (; j < MIN(size - i, fifo_width); j++)
+			val |= *p++ << (j * 8);
+		write32(fifo, val);
+		val = 0;
+		j = 0;
+	}
+
+}