device/mmio.h: Add bit field helpers

When accessing register with multiple bit fields, the common approach is
to use clrsetbits_le32, for example:

  clrsetbits(&reg, (1 << 0) | (0x3 << 1) | (0x7 << 10),
                   (1 << 0) | (0x1 << 1) | (0x5 << 10));

This hard to maintain because we have to calculate the mask values
manually, make sure the duplicated shift (offset) was set correctly.
And it may be even worse if the value to set will be based on some
runtime values (that many developers will do a if-block with two very
similar argument list), and leaving lots of magic numbers.

We want to encourage developers always giving field names, and have a
better way of setting fields. The proposed utility macros are:

 DEFINE_BITFIELD(name, high_bit, low_bit)
 EXTRACT_BITFIELD(value, name)
 WRITE32_BITFIELDS(addr, name, value, [name2, value2, ...])
 READ32_BITFIELD(addr, name)

Where a developer can easily convert from data sheet like

 BITS  NAME
 26:24 SEC_VIO

Into a declaration

 DEFINE_BITFIELD(SEC_VIO, 26, 24)

Then, a simple call can set the field as:

 WRITE32_BITFIELDS(&reg, SEC_VIO, 2);

That is much easier to understand than

 clrsetbits_le32(&reg, 0x7 << 24, 0x2 << 24);

And to extract the value:

 READ32_BITFIELD(&reg, SEC_VIO)

That is equivalent to:

 (read32(&reg) & 0x3) >> 24

Change-Id: I8a1b17142f7a7dc6c441b0b1ee67d60d73ec8cc8
Signed-off-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/35463
Reviewed-by: Julius Werner <jwerner@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/include/device/mmio.h

@@ -51,6 +51,126 @@ static inline void buffer_to_fifo32(void *buffer, size_t size, void *fifo,
 	buffer_to_fifo32_prefix(buffer, size, 0, 0, fifo,
 				fifo_stride, fifo_width);
 }
+
+/*
+ * Utilities to help processing bit fields.
+ *
+ * To define a bit field (usually inside a register), do:
+ *
+ *  DEFINE_BITFIELD(name, high_bit, low_bit)
+ *
+ *  - name: Name of the field to access.
+ *  - high_bit: highest bit that's part of the bit field.
+ *  - low_bit: lowest bit in the bit field.
+ *
+ * To extract one field value from a raw reg value:
+ *
+ *  EXTRACT_BITFIELD(value, name);
+ *
+ * To read from an MMIO register and extract one field from it:
+ *
+ *  READ32_BITFIELD(&reg, name);
+ *
+ * To write into an MMIO register, set given fields (by names) to specified
+ * values, and all other bits to zero (usually used for resetting a register):
+ *
+ *  WRITE32_BITFIELDS(&reg, name, value, [name, value, ...])
+ *
+ * To write into an MMIO register, set given fields (by names) to specified
+ * values, and leaving all others "unchanged" (usually used for updating some
+ * settings):
+ *
+ *  SET32_BITFIELDS(&reg, name, value, [name, value, ...])
+ *
+ * Examples:
+ *
+ *  DEFINE_BITFIELD(DISP_TYPE, 2, 1)
+ *  DEFINE_BITFIELD(DISP_EN, 0, 0)
+ *
+ *  SET32_BITFIELDS(&disp_regs.ctrl, DISP_TYPE, 2);
+ *  SET32_BITFIELDS(&disp_regs.ctrl, DISP_EN, 0);
+ *
+ *  SET32_BITFIELDS(&disp_regs.ctrl, DISP_TYPE, 1, DISP_EN, 1);
+ *  WRITE32_BITFIELDS(&disp_regs.ctrl, DISP_TYPE, 1, DISP_EN, 1);
+ *
+ *  READ32_BITFIELD(&reg, DISP_TYPE)
+ *  EXTRACT_BITFIELD(value, DISP_TYPE)
+ *
+ * These will be translated to:
+ *
+ *  clrsetbits_le32(&disp_regs.ctrl, 0x6, 0x4);
+ *  clrsetbits_le32(&disp_regs.ctrl, 0x1, 0x0);
+ *
+ *  clrsetbits_le32(&disp_regs.ctrl, 0x7, 0x3);
+ *  write32(&disp_regs.ctrl, 0x3);
+ *
+ *  (read32(&reg) & 0x6) >> 1
+ *  (value & 0x6) >> 1
+ *
+ * The {WRITE,SET}32_BITFIELDS currently only allows setting up to 8 fields at
+ * one invocation.
+ */
+
+#define DEFINE_BITFIELD(name, high_bit, low_bit) \
+	_Static_assert(high_bit >= low_bit, "invalid bit field range"); \
+	enum { \
+		name##_BITFIELD_SHIFT = (low_bit), \
+		name##_BITFIELD_SIZE = (high_bit) - (low_bit) + 1, \
+	};
+
+#define _BF_MASK(name, value) \
+	(((1 << name##_BITFIELD_SIZE) - 1) << name##_BITFIELD_SHIFT)
+
+#define _BF_VALUE(name, value) \
+	((value) << name##_BITFIELD_SHIFT)
+
+#define _BF_APPLY1(op, name, value, ...) (op(name, value))
+#define _BF_APPLY2(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY1(op, __VA_ARGS__))
+#define _BF_APPLY3(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY2(op, __VA_ARGS__))
+#define _BF_APPLY4(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY3(op, __VA_ARGS__))
+#define _BF_APPLY5(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY4(op, __VA_ARGS__))
+#define _BF_APPLY6(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY5(op, __VA_ARGS__))
+#define _BF_APPLY7(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY6(op, __VA_ARGS__))
+#define _BF_APPLY8(op, name, value, ...) ((op(name, value)) | \
+		_BF_APPLY7(op, __VA_ARGS__))
+#define _BF_APPLYINVALID(...) \
+		_Static_assert(0, "Invalid arguments for {WRITE,SET}*_BITFIELDS")
+
+#define _BF_IMPL2(op, addr, \
+	n1, v1, n2, v2, n3, v3, n4, v4, n5, v5, n6, v6, n7, v7, n8, v8, \
+	NARGS, ...) \
+	\
+	op(addr, \
+	   _BF_APPLY##NARGS(_BF_MASK, n1, v1, n2, v2, n3, v3, n4, v4, \
+			    n5, v5, n6, v6, n7, v7, n8, v8), \
+	   _BF_APPLY##NARGS(_BF_VALUE, n1, v1, n2, v2, n3, v3, n4, v4, \
+			    n5, v5, n6, v6, n7, v7, n8, v8))
+
+#define _BF_IMPL(op, addr, ...) \
+	_BF_IMPL2(op, addr, __VA_ARGS__, \
+		  8, INVALID, 7, INVALID, 6, INVALID, 5, INVALID, \
+		  4, INVALID, 3, INVALID, 2, INVALID, 1, INVALID)
+
+#define _WRITE32_BITFIELDS_IMPL(addr, masks, values) write32(addr, values)
+
+#define WRITE32_BITFIELDS(addr, ...)  \
+	_BF_IMPL(_WRITE32_BITFIELDS_IMPL, addr, __VA_ARGS__)
+
+#define SET32_BITFIELDS(addr, ...) \
+	_BF_IMPL(clrsetbits_le32, addr, __VA_ARGS__)
+
+#define EXTRACT_BITFIELD(value, name) \
+	(((value) & _BF_MASK(name, 0)) >> name##_BITFIELD_SHIFT)
+
+#define READ32_BITFIELD(addr, name) \
+	EXTRACT_BITFIELD(read32(addr), name)
+
 #endif	/* !__ROMCC__ */
 
 #endif	/* __DEVICE_MMIO_H__ */