Linux mainline fork with MSM8998 patches | https://mainline.space | Currently supported devices:
OnePlus 5/5T, Xiaomi Mi 6, F(x)tec Pro¹ (2019 QX1000 model) & Sony Xperia XZ Premium (UNTESTED!)
e440e30e26
At boot time the following happens:
1. Device core gets ready to probe our SPI driver.
2. Device core applies SPI controller's "default" pinctrl.
3. Device core calls the SPI driver's probe() function which will
eventually setup the chip select GPIO as "unasserted".
Thinking about the above, we can find:
a) For SPI devices that the BIOS inits (Cr50 and EC), the BIOS would
have had them configured as "GENI" pins and not as "GPIO" pins.
b) It turns out that our BIOS also happens to init these pins as
"output" (even though it doesn't need to since they're not muxed as
GPIO) but leaves them at the default state of "low".
c) As soon as we apply the "default" chip select it'll switch the
function to GPIO and stop driving the chip select high (which is
how "GENI" was driving it) and start driving it low.
d) As of commit 9378f46040be ("UPSTREAM: spi: spi-geni-qcom: Use the
new method of gpio CS control"), when the SPI core inits things it
inits the GPIO to be "deasserted". Prior to that commit the GPIO
was left untouched until first use.
e) When the first transaction happens we'll assert the chip select and
then deassert it after done.
So before the commit to change us to use gpio descriptors we used to
have a _really long_ assertion of chip select before our first
transaction (because it got pulled down and then the first "assert"
was a no-op). That wasn't great but (apparently) didn't cause any
real harm.
After the commit to change us to use gpio descriptors we end up
glitching the chip select line during probe. It would go low and then
high with no data transferred. The other side ought to be robust
against this, but it certainly could cause some confusion. It's known
to at least cause an error message on the EC console and it's believed
that, under certain timing conditions, it could be getting the EC into
a confused state causing the EC driver to fail to probe.
Let's fix things to avoid the glitch. We'll add an extra pinctrl
entry that sets the value of the pin to output high (CS deasserted)
before doing anything else. We'll do this in its own pinctrl node
that comes before the normal pinctrl entries to ensure that the order
is correct and that this gets applied before the mux change.
This change is in the trogdor board file rather than in the SoC dtsi
file because chip select polarity can be different depending on what's
hooked up and it doesn't feel worth it to spam the SoC dtsi file with
both options. The board file would need to pick the right one anyway.
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Fixes:
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|---|---|---|
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| 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 | ||
| Kconfig | ||
| MAINTAINERS | ||
| 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.