On Wed, Mar 28, 2018 at 02:25:12PM +0200, Boris Brezillon wrote:
On Wed, 28 Mar 2018 14:22:36 +0200 Daniel Vetter daniel@ffwll.ch wrote:
On Wed, Mar 28, 2018 at 09:34:54AM +0200, Boris Brezillon wrote:
Hi Peter,
On Mon, 26 Mar 2018 09:35:02 +0200 Peter Rosin peda@axentia.se wrote:
I have an sama5d31-based system with 64MB of memory and a 1920x1080 LVDS display wired for 16-bpp. When I enable legacy fbdev support, the contiguous memory allocator invariably fails with the order-11 allocation for a 1920x1080@24-bpp buffer (~6MB). But this HW can never make any good use of RGB888, so that is a wasted attempt anyway that would also waste precious memory should it succeed.
Sure, I could rewrite user-space to go directly to KMS etc, and that makes the (attempted) order-11 allocation go away, replacing it with one order-10 allocation per application restart for a 1920x1080@16-bpp buffer (<4MB). But after a few restarts, order-10 allocations start to fail as well, which is only to be expected AFAIU.
So, I'd rather not change user-space (which was originally written to target a smaller display) so that I at the same time get the benefit of an early pre-allocated fbdev frame-buffer that can be reused over and over. But to do that I need to tell the driver that 16-bpp is the preferred depth. Add a module parameter to do just that.
Signed-off-by: Peter Rosin peda@axentia.se
drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-)
I found some inspiration regarding naming and implementation here: https://patchwork.kernel.org/patch/9848631/
I have found no feedback on that patch though, which makes me wonder if I'm perhaps barking up the wronig tree?
Hm, isn't that something you can already overload with the video= parameter?
video=<output>:<resolution>[-<bpp>]
AFAIR, <bpp> encodes the color depth, so what is the benefit of adding this new property to overload the default depth?
Maybe I'm wrong and the default depth param is actually useful, but in this case we should probably make it generic since other drivers seems to need it too, and we might want to attach it to a specific display engine instance.
I think for the drm's fbdev emulation we ignore the bpp ...
Nope, it's already parsed [1].
[1]https://elixir.bootlin.com/linux/v4.16-rc3/source/drivers/gpu/drm/drm_fb_hel...
Oh, totally missed this. I honestly wonder why we then have all the various bpp module options in different drivers ... -Daniel