[RFC 0/6] drm: Add support for userspace drivers

[Martin Peres]

On 04/01/17 17:06, Daniel Vetter wrote:
> On Wed, Jan 04, 2017 at 02:34:36PM +0100, Noralf Trønnes wrote:
>> Hi,
>>
>> I was previously working on tinydrm as a replacement for staging/fbtft.
>> During a break from that work, I started to think about if it would be
>> possible to move the drivers to userspace instead. No point in having
>> them in the kernel if it's not necessary.
>>
>> This patchset includes all the pieces necessary to get a userspace
>> driver[1] working that is compatible with the fbtft/fb_ili9341 driver.
>> It is tested with a SPI interfaced display hat/shield for the Raspberry Pi,
>> which has an eeprom with a Device Tree fragment on it (merged by the
>> bootloader). With the help of udev and systemd, the driver is able to
>> autoload when the display is connected.
>> Performance wise, the kernel driver can do ~19fps on a 320x240 spi at 32MHz
>> display, whereas the userspace version does ~18fps. So performance is not
>> an argument to keep the driver in the kernel.
>>
>> What do you think about this approach?
>
> It's a pretty nifty thing, and iirc some of the ideas for implementing
> miracast centered around the same idea: Small userspace drm driver shim
> that forwards everything to the miracast code running all in userspace.
> David Herrmann looked into that years ago, not sure he ever got the full
> stack up&running.

This is actually something David Herrmann told us not to do, stating 
that it was too hard for Desktop Environments to select which GPUs to 
output to. I however disagreed as this is something they need to support 
anyway for USB GPUs and miracast could piggy back on this effort.

An engineer in Intel Finland did work on this and we got approval for 
Open Sourcing it but I really have no time for this right now though :s

That was my 2 cents.

Martin