On Mon 01 Jun 2015 16:26:17 Frederic Muller wrote:

> Hi!

>

> I connect one of my machines to my TVs. I have noticed that since

> sometimes along F21 updates the specific TV resolution could not longer

> be activated. As it is definitely not a life threatening condition I

> thought another update would fix it. Apparently the problem might lay

> elsewhere...

>

> So I have 2 TVs (with different resolution) to test. I start with cvt,

> then xrandr --newmode, xrandr --addmode and then --output.

You should be getting EDID back from the screen that can be used to set the mode.

You should see the EDID with xrandr --verbose.

It is worth looking at the dmesg output to see it the kernel had a problem with the connection.

There is a patch in kernel 4.1 that can help with EDID read problems that might be what you are seeing. (Spec says 1 bytes read are good, but vendors sometimes only work with 16 bytes read as that is what Windows does).

Barry