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1e2d08a837
There's a bit of math in rockchip_mmc_get_phase() to calculate the
"fine delay". This math boils down to:
PSECS_PER_SEC = 1000000000000.
ROCKCHIP_MMC_DELAY_ELEMENT_PSEC = 60
card_clk * ROCKCHIP_MMC_DELAY_ELEMENT_PSEC * 360 * x / PSECS_PER_SEC
...but we do it in pieces to avoid overflowing 32-bits. Right now we
overdo it a little bit, though, and end up getting less accurate math
than we could. Right now we do:
DIV_ROUND_CLOSEST((card_clk / 1000000) *
(ROCKCHIP_MMC_DELAY_ELEMENT_PSEC / 10) *
(360 / 10) *
delay_num,
PSECS_PER_SEC / 1000000 / 10 / 10)
This is non-ideal because:
A) The pins on Rockchip SoCs are rated to go at most 150 MHz, so the
max card clock is 150 MHz. Even ignoring this the maximum SD card
clock (for SDR104) would be 208 MHz. This means you can decrease
your division by 100x and still not overflow:
hex(208000000 / 10000 * 6 * 36 * 0xff) == 0x44497200
B) On many Rockchip SoCs we end up with a card clock that is actually
148500000 because we parent off the 297 MHz PLL. That means the
math we're actually doing today is less than ideal. Specifically:
148500000 / 1000000 = 148
Let's fix the math to be slightly more accurate.
NOTE: no known problems are fixed by this. It was found simply by
code inspection. If you want to see the difference between the old
and the new on a 148.5 MHz clock, this python can help:
old = [x for x in
(int(round(148 * 6 * 36 * x / 10000.)) for x in range(256))
if x < 90]
new = [x for x in
(int(round(1485 * 6 * 36 * x / 100000.)) for x in range(256))
if x < 90]
The only differences are:
delay_num=17 54=>55
delay_num=22 70=>71
delay_num=27 86=>87
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
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| certs | ||
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| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
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| Makefile | ||
| README | ||
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.