add stmac read mac form eeprom

hc

2023-12-09 b22da3d8526a935aa31e086e63f60ff3246cb61c

 kernel/drivers/md/bcache/util.h
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@@ -558,17 +558,29 @@
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 	return crc;
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 }
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-/* Does linear interpolation between powers of two */
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+/*
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+ * A stepwise-linear pseudo-exponential.  This returns 1 << (x >>
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+ * frac_bits), with the less-significant bits filled in by linear
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+ * interpolation.
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+ *
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+ * This can also be interpreted as a floating-point number format,
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+ * where the low frac_bits are the mantissa (with implicit leading
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+ * 1 bit), and the more significant bits are the exponent.
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+ * The return value is 1.mantissa * 2^exponent.
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+ *
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+ * The way this is used, fract_bits is 6 and the largest possible
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+ * input is CONGESTED_MAX-1 = 1023 (exponent 16, mantissa 0x1.fc),
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+ * so the maximum output is 0x1fc00.
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+ */
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 static inline unsigned int fract_exp_two(unsigned int x,
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 					 unsigned int fract_bits)
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 {
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-	unsigned int fract = x & ~(~0 << fract_bits);
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+	unsigned int mantissa = 1 << fract_bits;	/* Implicit bit */
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-	x >>= fract_bits;
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-	x   = 1 << x;
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-	x  += (x * fract) >> fract_bits;
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-
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-	return x;
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+	mantissa += x & (mantissa - 1);
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+	x >>= fract_bits;	/* The exponent */
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+	/* Largest intermediate value 0x7f0000 */
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+	return mantissa << x >> fract_bits;
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 }
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 void bch_bio_map(struct bio *bio, void *base);