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2ee471a1e2
If you added a bit of a delay (like a trace_printk) into the ISR for
the spi-geni-qcom driver, you would suddenly start seeing some errors
spit out. The problem was that, though the ISR itself held a lock,
other parts of the driver didn't always grab the lock.
One example race was this:
CPU0 CPU1
---- ----
spi_geni_set_cs()
mas->cur_mcmd = CMD_CS;
geni_se_setup_m_cmd(...)
wait_for_completion_timeout(&xfer_done);
<INTERRUPT>
geni_spi_isr()
complete(&xfer_done);
<wakeup>
pm_runtime_put(mas->dev);
... // back to SPI core
spi_geni_transfer_one()
setup_fifo_xfer()
mas->cur_mcmd = CMD_XFER;
mas->cur_cmd = CMD_NONE; // bad!
return IRQ_HANDLED;
Let's fix this. Before we start messing with hardware, we'll grab the
lock to make sure that the IRQ handler from some previous command has
really finished. We don't need to hold the lock unless we're in a
state where more interrupts can come in, but we at least need to make
sure the previous IRQ is done. This lock is used exclusively to
prevent the IRQ handler and non-IRQ from stomping on each other. The
SPI core handles all other mutual exclusion.
As part of this, we change the way that the IRQ handler detects
spurious interrupts. Previously we checked for our state variable
being set to IRQ_NONE, but that was done outside the spinlock. We
could move it into the spinlock, but instead let's just change it to
look for the lack of any IRQ status bits being set. This can be done
outside the lock--the hardware certainly isn't grabbing or looking at
the spinlock when it updates its status register.
It's possible that this will fix real (but very rare) errors seen in
the field that look like:
irq ...: nobody cared (try booting with the "irqpoll" option)
NOTE: an alternate strategy considered here was to always make the
complete() / spi_finalize_current_transfer() the very last thing in
our IRQ handler. With such a change you could consider that we could
be "lockless". In that case, though, we'd have to be very careful w/
memory barriers so we made sure we didn't have any bugs with weakly
ordered memory. Using spinlocks makes the driver much easier to
understand.
Fixes:
|
||
|---|---|---|
| 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.