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@xxxxxxxx> 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@xxxxxxxxxx> 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@xxxxxxxxxx> > > > > --- > > > > 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_helper.c#L1812 Oh, totally missed this. I honestly wonder why we then have all the various bpp module options in different drivers ... -Daniel -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
