Hello. On 11-05-2012 22:12, Sarah Sharp wrote:
For external ports, this should be associated with sys file control. The users need to determine when they should be power off.
You don't mean "external", you mean "not described as unconnectable by ACPI".
So I should work on the external ports without devices firstly and add the sys file for user to control?
Yes, I think so. It will be less controversial and probably simpler. When that mechanism is ready, you should be able to use it automatically for unconnectable ports.
One tricky thing: In theory, there should be a separate sysfs file for each port. That seems like a lot of overhead though; is there any way to present the information in a single file that won't offend sysfs purists?
Tianyu proposed having one file per hub, with a bit field that controlled each port power. However, I was concerned about different userspace applications racing with each other to turn or off ports. For example, one app could read the bit field, attempt to power off just port 1, but before it can write to the sysfs file, a second app powers on port2, and the first app then writes to the sysfs file, leaving port 1 powered off, and port 2 powered off, which is not what the second app wanted.
But if you can think of a better way to coalesce the port power off mechanisms into one file, we're all ears. :)
How about two files? You write 1 to the bit that matcheas port you want powered on in the 'poweron' file, and vice versa, you write 1 to the bit that matches port you want powered off in the 'poweroff' file.
Sarah Sharp
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