barebox runs code in pollers. This works reasonably well when the pollers do not touch any resources that are used by code outside the pollers as well. Currently we also have fastboot running in a poller and this is where things become dangerous. This series aims to provide a way for solving resource conflicts with pollers. It is currently enough to safely run the networking receive loop inside of pollers, but there are more possible issues, one of them described below. There are several more places that have to be sprinkled with: slices, the barebox idea of locking =================================== barebox has pollers which execute code in the background whenever one of the delay functions (udelay, mdelay, ...) or is_timeout() are called. This introduces resource problems when some device triggers a poller by calling a delay function and then the poller code calls into the same device again. As an example consider a I2C GPIO expander which drives a LED which shall be used as a heartbeat LED: poller -> LED on/off -> GPIO high/low -> I2C transfer The I2C controller has a timeout loop using is_timeout() and thus can trigger a poller run. With this the following can happen during an unrelated I2C transfer: I2C transfer -> is_timeout() -> poller -> LED on/off -> GPIO high/low -> I2C transfer We end up with issuing an I2C transfer during another I2C transfer and things go downhill. Due to the lack of interrupts we can't do real locking in barebox. We use a mechanism called slices instead. A slice describes a resource to which other slices can be attached. Whenever a slice is needed it must be acquired. Acquiring a slice never fails, it just increases the acquired counter of the slice and its dependent slices. when a slice shall be used inside a poller it must first be tested if the slice is already in use. If it is, we can't do the operation on the slice now and must return and hope that we have more luck in the next poller call. slices can be attached other slices as dependencies. In the example above LED driver would add a dependency to the GPIO controller and the GPIO driver would add a dependency to the I2C bus: GPIO driver probe: slice_add(&gpio->slice, i2c_device_slice(i2cdev)); LED driver probe: slice_add(&led->slice, gpio_slice(gpio)); The GPIO code would call slice_acquire(&gpio->slice) before doing any operation on the GPIO chip providing this GPIO, likewise the I2C core would call slice_acquire(&i2cbus->slice) before doing an operation on this I2C bus. The heartbeat poller code would call slice_acquired(led_slice(led)) and only continue when the slice is not acquired. Sascha Sascha Hauer (8): Introduce slices net: Add a slice to struct eth_device net: mdiobus: Add slice usb: Add a slice to usb host controllers usbnet: Add slice net: Call net_poll() in a poller net: reply to ping requests usbnet: Be more friendly in the receive path common/Makefile | 1 + common/slice.c | 316 +++++++++++++++++++++++++++++++++++++ drivers/net/phy/mdio_bus.c | 40 +++++ drivers/net/phy/phy.c | 2 + drivers/net/usb/usbnet.c | 22 ++- drivers/usb/core/usb.c | 6 + fs/nfs.c | 2 - fs/tftp.c | 2 - include/linux/phy.h | 32 ++-- include/net.h | 11 +- include/slice.h | 31 ++++ include/usb/usb.h | 7 + include/usb/usbnet.h | 3 + net/dhcp.c | 1 - net/dns.c | 1 - net/eth.c | 29 +++- net/net.c | 60 ++++++- net/netconsole.c | 4 +- net/nfs.c | 1 - net/ping.c | 2 - net/sntp.c | 2 - 21 files changed, 524 insertions(+), 51 deletions(-) create mode 100644 common/slice.c create mode 100644 include/slice.h -- 2.25.1 _______________________________________________ barebox mailing list barebox@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/barebox
