Commit de2a3eae authored Apr 13, 2019 by Chen-Yu Tsai Committed by Greg Kroah-Hartman Apr 25, 2019

nvmem: sunxi_sid: Optimize register read-out method



SID cells are 32-bit aligned, and a multiple of 32 bits in length. The
only outlier is the thermal sensor calibration data, which is 16 bits
per sensor. However a whole 64 bits is allocated for this purpose, so
we could consider it conforming to the rule above.

Also, the register read-out method assumes native endian, unlike the
direct MMIO method, which assumes big endian. Thus no endian conversion
is involved.

Under these assumptions, the register read-out method can be slightly
optimized. Instead of reading one word then discarding 3 bytes, read
the whole word directly into the buffer. However, for reads under 4
bytes or trailing bytes, we still use a scratch buffer to extract the
requested bytes.

We could go one step further if .word_size was 4, but changing that
would affect the sysfs interface's behavior.

Signed-off-by: Chen-Yu Tsai <wens@csie.org>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

parent 9c4adfb5

drivers/nvmem/sunxi_sid.c

+18 −20

Original line number	Diff line number	Diff line
		@@ -115,35 +115,33 @@ static int sun8i_sid_register_readout(const struct sunxi_sid *sid,
		* to be not reliable at all.
		* Read by the registers instead.
		*/
		static int sun8i_sid_read_byte_by_reg(const struct sunxi_sid *sid,
		const unsigned int offset,
		u8 *out)
		static int sun8i_sid_read_by_reg(void *context, unsigned int offset,
		void *val, size_t bytes)
		{
		struct sunxi_sid *sid = context;
		u32 word;
		int ret;

		ret = sun8i_sid_register_readout(sid, offset & ~0x03, &word);

		/* .stride = 4 so offset is guaranteed to be aligned */
		while (bytes >= 4) {
		ret = sun8i_sid_register_readout(sid, offset, val);
		if (ret)
		return ret;

		out = (word >> ((offset & 0x3) 8)) & 0xff;

		return 0;
		val += 4;
		offset += 4;
		bytes -= 4;
		}

		static int sun8i_sid_read_by_reg(void *context, unsigned int offset,
		void *val, size_t bytes)
		{
		struct sunxi_sid *sid = context;
		u8 *buf = val;
		int ret;
		if (!bytes)
		return 0;

		while (bytes--) {
		ret = sun8i_sid_read_byte_by_reg(sid, offset++, buf++);
		/* Handle any trailing bytes */
		ret = sun8i_sid_register_readout(sid, offset, &word);
		if (ret)
		return ret;
		}

		memcpy(val, &word, bytes);

		return 0;
		}

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