Hi, On 02/13/2014 07:37 AM, Alexander E. Patrakov wrote: > 13.02.2014 04:26, David Herrmann wrote: >> The "attach" stuff actually sounds doable, but who decides which one >> to attach? You still need some user-space script during device-plug >> for that. >> But to be honest, the simplest way would be a "backlightd" >> bus-activatable daemon. SetBacklight() then takes a DRM-connector and >> brightness-value, which the daemon looks up in /sys and sets.. This >> has the advantage that we can do any fancy matching in user-space. We >> can provide quirks (maybe even via udev-hwdb) and other helpers for >> weird setups. > > What would be done with Samsung monitors (like an old SyncMaster 770P) that > have a DVI connection, no physical buttons and have to be controlled via > DDC-CI? Currently, ddccontrol works (via /dev/i2c-*), but only from root. I > would like this use case to be covered in such a way that it could work both > in Xorg and in Wayland, and, if possible, without races related to i2c usage > from the kernel and from userspace.
The nice thing about having a userspace daemon for this is that we can actually add some support for DCC-CI too. WRT races between user and kernelspace, those can be avoided by using the I2C_RDWR ioctl, in this case you can specify multipel i2c writes / reads which will all get executed as one transaction, note this assumes that the protocol supports repeated START conditions, if it needs a STOP condition and still needs everything to be in one transaction, then things become trickier. This also assumes that the i2c controller driver used supports I2C_FUNC_I2C Regards, Hans
