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author | 2019-04-13 11:32:50 +0100 | |
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committer | 2019-04-25 19:43:11 +0200 | |
commit | de2a3eaea552f2d562fae46bd495eb83298a1b3c (patch) | |
tree | 38ada939657cc218d0732829eb5413bd7d347abe /drivers/nvmem | |
parent | nvmem: sunxi_sid: Read out SID for randomness without looping (diff) | |
download | linux-de2a3eaea552.tar.gz linux-de2a3eaea552.tar.bz2 linux-de2a3eaea552.zip |
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>
Diffstat (limited to 'drivers/nvmem')
-rw-r--r-- | drivers/nvmem/sunxi_sid.c | 38 |
1 files changed, 18 insertions, 20 deletions
diff --git a/drivers/nvmem/sunxi_sid.c b/drivers/nvmem/sunxi_sid.c index 704c35edf796..15fbfab62595 100644 --- a/drivers/nvmem/sunxi_sid.c +++ b/drivers/nvmem/sunxi_sid.c @@ -115,36 +115,34 @@ 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) -{ - u32 word; - int ret; - - ret = sun8i_sid_register_readout(sid, offset & ~0x03, &word); - - if (ret) - return ret; - - *out = (word >> ((offset & 0x3) * 8)) & 0xff; - - return 0; -} - 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; + u32 word; int ret; - while (bytes--) { - ret = sun8i_sid_read_byte_by_reg(sid, offset++, buf++); + /* .stride = 4 so offset is guaranteed to be aligned */ + while (bytes >= 4) { + ret = sun8i_sid_register_readout(sid, offset, val); if (ret) return ret; + + val += 4; + offset += 4; + bytes -= 4; } + if (!bytes) + return 0; + + /* Handle any trailing bytes */ + ret = sun8i_sid_register_readout(sid, offset, &word); + if (ret) + return ret; + + memcpy(val, &word, bytes); + return 0; } |