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Tony notes that the GPIO module does not idle when level interrupts are in use, as the wakeup appears to get stuck. After extensive investigation, it appears that the wakeup will only be cleared if the interrupt status register is cleared while the interrupt is enabled. However, we are currently clearing it with the interrupt disabled for level-based interrupts. It is acknowledged that this observed behaviour conflicts with a statement in the TRM: CAUTION After servicing the interrupt, the status bit in the interrupt status register (GPIOi.GPIO_IRQSTATUS_0 or GPIOi.GPIO_IRQSTATUS_1) must be reset and the interrupt line released (by setting the corresponding bit of the interrupt status register to 1) before enabling an interrupt for the GPIO channel in the interrupt-enable register (GPIOi.GPIO_IRQSTATUS_SET_0 or GPIOi.GPIO_IRQSTATUS_SET_1) to prevent the occurrence of unexpected interrupts when enabling an interrupt for the GPIO channel. However, this does not appear to be a practical problem. Further, as reported by Grygorii Strashko <grygorii.strashko@ti.com>, the TI Android kernel tree has an earlier similar patch as "GPIO: OMAP: Fix the sequence to clear the IRQ status" saying: if the status is cleared after disabling the IRQ then sWAKEUP will not be cleared and gates the module transition When we unmask the level interrupt after the interrupt has been handled, enable the interrupt and only then clear the interrupt. If the interrupt is still pending, the hardware will re-assert the interrupt status. Should the caution note in the TRM prove to be a problem, we could use a clear-enable-clear sequence instead. Cc: Aaro Koskinen <aaro.koskinen@iki.fi> Cc: Keerthy <j-keerthy@ti.com> Cc: Peter Ujfalusi <peter.ujfalusi@ti.com> Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk> [tony@atomide.com: updated comments based on an earlier TI patch] Signed-off-by: Tony Lindgren <tony@atomide.com> Acked-by: Grygorii Strashko <grygorii.strashko@ti.com> Signed-off-by: Linus Walleij <linus.walleij@linaro.org> |
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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.