[Intel-gfx] Can recent i915 support more than 8192x8192 screen?

[Rodrigo Vivi]

On Thu, Jul 19, 2018 at 11:31:19PM +0200, Marcin Owsiany wrote:
>    Hello,
>    TL;DR: how can I set a 8960x2880 screen (not display) size on a T580? A
>    patch for i915 that I found on the internets does not seem to work.
>    Full story:
>    I'm a rather happy user of ThinkPad T580 which comes with a
>    high-density 3840x2160 LCD, and the following graphics hardware.
>    00:02.0 VGA compatible controller: Intel Corporation Device 5917 (rev
>    07) (prog-if 00 [VGA controller])
>            Subsystem: Lenovo Device 225a
>            Flags: bus master, fast devsel, latency 0, IRQ 142
>            Memory at e7000000 (64-bit, non-prefetchable) [size=16M]
>            Memory at c0000000 (64-bit, prefetchable) [size=256M]
>            I/O ports at e000 [size=64]
>            [virtual] Expansion ROM at 000c0000 [disabled] [size=128K]
>            Capabilities: [40] Vendor Specific Information: Len=0c <?>
>            Capabilities: [70] Express Root Complex Integrated Endpoint,
>    MSI 00
>            Capabilities: [ac] MSI: Enable+ Count=1/1 Maskable- 64bit-
>            Capabilities: [d0] Power Management version 2
>            Capabilities: [100] Process Address Space ID (PASID)
>            Capabilities: [200] Address Translation Service (ATS)
>            Capabilities: [300] Page Request Interface (PRI)
>            Kernel driver in use: i915
>            Kernel modules: i915
>    Unfortunately attaching it to an external normal-density 2560x1440
>    display means I need to apply scaling. Combined with the side-by-side
>    arrangement of monitors, this means I'd need to set screen size
>    to 8960x2880. However this does not work:
>     $ xrandr --fb 8960x2880
>     xrandr: screen cannot be larger than 8192x8192 (desired size
>    8960x2880)
>    I found this [1]thread on reddit about the same problem, where a user
>    posted a simple patch claimed to be supplied by someone on #intel-gfx.
>    Unfortunately it does not work (or at least is not sufficient) - after
>    applying it xrandr does claim that 16384x16384 is possible, but
>    actually trying to use more than 8192x8192 fails with an error
>    (unfortunately I lost the exact message).

I'm afraid that it is a hardware limitation that you won't be able to
workaround. But a log would be interesting anyway... (both dmesg and xorg.0.log)

>    My current workaround is to pretend that the displays are arranged
>    vertically, but even after a few months I'm sometimes having trouble
>    remembering that I need to move mouse cursor UP when I want to go to
>    LEFT display :-)

This is another bug.... And probably the right (only?) fixable fr your
setup.

>    I wonder if someone could help me here. Even just getting a definite
>    answer on whether my hardware can in theory support this or not would
>    be helpful, since I found conflicting information.

Well, I'm afraid the right information is already there on the first
xrandr output. The rest was just misleading you.

>    FWIW I'm on Debian stable, Linux 4.9.8x.
>    regards,
>    Marcin
> 
> References
> 
>    1. https://www.reddit.com/r/linux/comments/6bghzm/increasing_maximum_xorg_virtual_screen_resolution/

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