On 09/02/2009 07:32 AM, Michael Krufky wrote:
Over the course of the past year, a number of developers have expressed a need for giving the bridge drivers better control over dvb_frontend operations. Specifically, there is a need for the bridge driver to receive a DVB frontend IOCTL and have the opportunity to allow or deny the IOCTL to proceed, as resources permit. For instance, in the case of a hybrid device, only the bridge driver knows whether the analog functionality is presently being used. If the driver is currently in analog mode, serving video frames, the driver will have a chance to deny the DVB frontend ioctl request before dvb-core passes the request on to the frontend driver, potentially damaging the analog video stream already in progress. In some cases, the bridge driver might have to perform a setup operation to use a feature specific to the device. For instance, the bridge device may be in a low powered state - this new capability allows the driver to wake up before passing the command on to the frontend driver. This new feature will allow LinuxTV developers to finally get working on actual power management support within the v4l/dvb subsystem, without the fear of breaking devices with hybrid analog / digital functionality. In other cases, there may be situations in which multiple RF connectors are available to the tuner, but only the bridge driver will be aware of this, as this type of thing is specific to the device's hardware implementation. As there are many tuners capable of multiple RF spigots, not all devices actually employ this feature - only the bridge driver knows what implementations support such features, and how to enable / disable them. The possibilities are endless. I actually did all the heavy lifting involved in this a few months ago, but haven't had a moment to write up this RFC until now. The change to dvb-core that allows this new functionality is posted to my development repository on kernellabs.com. I have also included an example of how this can be used on a digital tuner board with multiple RF inputs. The multiple RF input switching is already supported in today's code, but I promised Mauro that I would present a better method of doing this before the upcoming merge window. For your review and comments, please take a look at the topmost changesets, starting with "create a standard method for dvb adapter drivers to override frontend ioctls": http://kernellabs.com/hg/~mkrufky/fe_ioctl_override
Idea looks very good! I tested one DVB USB device need blocking IOCTLs when demod and tuner are power save and didn't saw functionality problems.
However, it was a little bit hard to add callback to DVB USB driver. Could that callback be added to the struct dvb_usb_adapter_properties for simplify things? I have feeling that this callback will be useful most DVb USB devices - setting GPIOs and clock settings for power save.
Name fe_ioctl_override sounds like whole IOCTL will be replaced with new one which is not true. Still, I don't know which could be better name.
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