linux-kernel - Re: [PATCH 2/3] gpu/drm: ingenic: Switch emulated fbdev to 16bpp

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Date:   Mon, 17 Feb 2020 10:30:01 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        od@...c.me, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] gpu/drm: ingenic: Switch emulated fbdev to 16bpp

On Sun, Feb 16, 2020 at 12:58:10PM -0300, Paul Cercueil wrote:
> The fbdev emulation is only ever used on Ingenic SoCs to run old SDL1
> based games at 16bpp (rgb565). Recent applications generally talk to
> DRM directly, and can request their favourite pixel format; so we can
> make everybody happy by switching the emulated fbdev to 16bpp.
> 
> Signed-off-by: Paul Cercueil <paul@...pouillou.net>
> ---
>  drivers/gpu/drm/ingenic/ingenic-drm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/ingenic/ingenic-drm.c b/drivers/gpu/drm/ingenic/ingenic-drm.c
> index 034961a40e98..9aa88fabbd2a 100644
> --- a/drivers/gpu/drm/ingenic/ingenic-drm.c
> +++ b/drivers/gpu/drm/ingenic/ingenic-drm.c
> @@ -808,7 +808,7 @@ static int ingenic_drm_probe(struct platform_device *pdev)
>  		goto err_devclk_disable;
>  	}
>  
> -	ret = drm_fbdev_generic_setup(drm, 32);
> +	ret = drm_fbdev_generic_setup(drm, 16);

If you're really bored, could we make everyone even more happy by exposing
format switching in the drm fbdev emulation? Only for the drivers which
have a full format list on the primary plane (gets too tricky otherwise).
And obviously only formats that have lower bpp than the one we booted with
(can't reallocate the framebuffer because fbdev).

Just as an idea, this shouldn't be too horrible amounts of work to wire
up. But ofc more than this oneliner :-)

Cheers, Daniel

>  	if (ret)
>  		dev_warn(dev, "Unable to start fbdev emulation: %i", ret);
>  
> -- 
> 2.25.0
> 

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