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SubjectRe: [PATCH] drm/atmel-hlcdc: add command line option to specify preferred depth
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 ...

But yeah probably worth it to wire it up properly.
-Daniel
>
> Thanks,
>
> Boris
>
> >
> > Cheers,
> > Peter
> >
> > diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c
> > index c1ea5c36b006..f0148627c221 100644
> > --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c
> > +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_dc.c
> > @@ -29,6 +29,11 @@
> >
> > #define ATMEL_HLCDC_LAYER_IRQS_OFFSET 8
> >
> > +static int atmel_hlcdc_preferred_depth __read_mostly;
> > +
> > +MODULE_PARM_DESC(preferreddepth, "Set preferred bpp");
> > +module_param_named(preferreddepth, atmel_hlcdc_preferred_depth, int, 0400);
> > +
> > static const struct atmel_hlcdc_layer_desc atmel_hlcdc_at91sam9n12_layers[] = {
> > {
> > .name = "base",
> > @@ -590,6 +595,7 @@ static int atmel_hlcdc_dc_modeset_init(struct drm_device *dev)
> > dev->mode_config.min_height = dc->desc->min_height;
> > dev->mode_config.max_width = dc->desc->max_width;
> > dev->mode_config.max_height = dc->desc->max_height;
> > + dev->mode_config.preferred_depth = 24;
> > dev->mode_config.funcs = &mode_config_funcs;
> >
> > return 0;
> > @@ -658,7 +664,7 @@ static int atmel_hlcdc_dc_load(struct drm_device *dev)
> >
> > platform_set_drvdata(pdev, dev);
> >
> > - drm_fb_cma_fbdev_init(dev, 24, 0);
> > + drm_fb_cma_fbdev_init(dev, atmel_hlcdc_preferred_depth, 0);
> >
> > drm_kms_helper_poll_init(dev);
> >
> > @@ -756,6 +762,16 @@ static int atmel_hlcdc_dc_drm_probe(struct platform_device *pdev)
> > struct drm_device *ddev;
> > int ret;
> >
> > + switch (atmel_hlcdc_preferred_depth) {
> > + case 0: /* driver default */
> > + case 8:
> > + case 16:
> > + case 24:
> > + break;
> > + default:
> > + return -EINVAL;
> > + }
> > +
> > ddev = drm_dev_alloc(&atmel_hlcdc_dc_driver, &pdev->dev);
> > if (IS_ERR(ddev))
> > return PTR_ERR(ddev);
>
>
>
> --
> Boris Brezillon, Bootlin (formerly Free Electrons)
> Embedded Linux and Kernel engineering
> https://bootlin.com
> _______________________________________________
> dri-devel mailing list
> dri-devel@lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

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