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1/* SPDX-License-Identifier: GPL-2.0
2 *
3 * Various common functions used by the framebuffer drawing code
4 *
5 * Copyright (C) 2025 Zsolt Kajtar (soci@c64.rulez.org)
6 */
7#ifndef _FB_DRAW_H
8#define _FB_DRAW_H
9
10/* swap bytes in a long, independent of word size */
11#define swab_long _swab_long(BITS_PER_LONG)
12#define _swab_long(x) __swab_long(x)
13#define __swab_long(x) swab##x
14
15/* move the address pointer by the number of words */
16static inline void fb_address_move_long(struct fb_address *adr, int offset)
17{
18 adr->address += offset * (BITS_PER_LONG / BITS_PER_BYTE);
19}
20
21/* move the address pointer forward with the number of bits */
22static inline void fb_address_forward(struct fb_address *adr, unsigned int offset)
23{
24 unsigned int bits = (unsigned int)adr->bits + offset;
25
26 adr->bits = bits & (BITS_PER_LONG - 1u);
27 adr->address += (bits & ~(BITS_PER_LONG - 1u)) / BITS_PER_BYTE;
28}
29
30/* move the address pointer backwards with the number of bits */
31static inline void fb_address_backward(struct fb_address *adr, unsigned int offset)
32{
33 int bits = adr->bits - (int)offset;
34
35 adr->bits = bits & (BITS_PER_LONG - 1);
36 if (bits < 0)
37 adr->address -= (adr->bits - bits) / BITS_PER_BYTE;
38 else
39 adr->address += (bits - adr->bits) / BITS_PER_BYTE;
40}
41
42/* compose pixels based on mask */
43static inline unsigned long fb_comp(unsigned long set, unsigned long unset, unsigned long mask)
44{
45 return ((set ^ unset) & mask) ^ unset;
46}
47
48/* framebuffer read-modify-write access for replacing bits in the mask */
49static inline void fb_modify_offset(unsigned long val, unsigned long mask,
50 int offset, const struct fb_address *dst)
51{
52 fb_write_offset(fb_comp(val, fb_read_offset(offset, dst), mask), offset, dst);
53}
54
55/*
56 * get current palette, if applicable for visual
57 *
58 * The pseudo color table entries (and colors) are right justified and in the
59 * same byte order as it's expected to be placed into a native ordered
60 * framebuffer memory. What that means:
61 *
62 * Expected bytes in framebuffer memory (in native order):
63 * RR GG BB RR GG BB RR GG BB ...
64 *
65 * Pseudo palette entry on little endian arch:
66 * RR | GG << 8 | BB << 16
67 *
68 * Pseudo palette entry on a big endian arch:
69 * RR << 16 | GG << 8 | BB
70 */
71static inline const u32 *fb_palette(struct fb_info *info)
72{
73 return (info->fix.visual == FB_VISUAL_TRUECOLOR ||
74 info->fix.visual == FB_VISUAL_DIRECTCOLOR) ? info->pseudo_palette : NULL;
75}
76
77/* move pixels right on screen when framebuffer is in native order */
78static inline unsigned long fb_right(unsigned long value, int index)
79{
80#ifdef __LITTLE_ENDIAN
81 return value << index;
82#else
83 return value >> index;
84#endif
85}
86
87/* move pixels left on screen when framebuffer is in native order */
88static inline unsigned long fb_left(unsigned long value, int index)
89{
90#ifdef __LITTLE_ENDIAN
91 return value >> index;
92#else
93 return value << index;
94#endif
95}
96
97/* reversal options */
98struct fb_reverse {
99 bool byte, pixel;
100};
101
102/* reverse bits of each byte in a long */
103static inline unsigned long fb_reverse_bits_long(unsigned long val)
104{
105#if defined(CONFIG_HAVE_ARCH_BITREVERSE) && BITS_PER_LONG == 32
106 return bitrev8x4(val);
107#else
108 val = fb_comp(val >> 1, val << 1, ~0UL / 3);
109 val = fb_comp(val >> 2, val << 2, ~0UL / 5);
110 return fb_comp(val >> 4, val << 4, ~0UL / 17);
111#endif
112}
113
114/* apply byte and bit reversals as necessary */
115static inline unsigned long fb_reverse_long(unsigned long val,
116 struct fb_reverse reverse)
117{
118 if (reverse.pixel)
119 val = fb_reverse_bits_long(val);
120 return reverse.byte ? swab_long(val) : val;
121}
122
123/* calculate a pixel mask for the given reversal */
124static inline unsigned long fb_pixel_mask(int index, struct fb_reverse reverse)
125{
126#ifdef FB_REV_PIXELS_IN_BYTE
127 if (reverse.byte)
128 return reverse.pixel ? fb_left(~0UL, index) : swab_long(fb_right(~0UL, index));
129 else
130 return reverse.pixel ? swab_long(fb_left(~0UL, index)) : fb_right(~0UL, index);
131#else
132 return reverse.byte ? swab_long(fb_right(~0UL, index)) : fb_right(~0UL, index);
133#endif
134}
135
136
137/*
138 * initialise reversals based on info
139 *
140 * Normally the first byte is the low byte on little endian and in the high
141 * on big endian. If it's the other way around then that's reverse byte order.
142 *
143 * Normally the first pixel is the LSB on little endian and the MSB on big
144 * endian. If that's not the case that's reverse pixel order.
145 */
146static inline struct fb_reverse fb_reverse_init(struct fb_info *info)
147{
148 struct fb_reverse reverse;
149#ifdef __LITTLE_ENDIAN
150 reverse.byte = fb_be_math(info) != 0;
151#else
152 reverse.byte = fb_be_math(info) == 0;
153#endif
154#ifdef FB_REV_PIXELS_IN_BYTE
155 reverse.pixel = info->var.bits_per_pixel < BITS_PER_BYTE
156 && (info->var.nonstd & FB_NONSTD_REV_PIX_IN_B);
157#else
158 reverse.pixel = false;
159#endif
160 return reverse;
161}
162
163#endif /* FB_DRAW_H */