linux-kernel - Re: [PATCH v2 2/3] gpu/drm: ingenic: Switch emulated fbdev to 16bpp

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Message-ID: <20200408120444.GJ3456981@phenom.ffwll.local>
Date:   Wed, 8 Apr 2020 14:04:44 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Daniel Vetter <daniel@...ll.ch>, David Airlie <airlied@...ux.ie>,
        od@...c.me, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] gpu/drm: ingenic: Switch emulated fbdev to 16bpp

On Wed, Feb 26, 2020 at 01:30:40AM -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.
> 
> v2: No change
> 
> 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 5493a80d7d2f..3f8cc98d41fe 100644
> --- a/drivers/gpu/drm/ingenic/ingenic-drm.c
> +++ b/drivers/gpu/drm/ingenic/ingenic-drm.c
> @@ -807,7 +807,7 @@ 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);

This will conflict with Thomas' work to remove the error code, so might
need a rebase. Now for the patch itself your supposed to set
drm_device->mode_config.preferred_bpp and leave this here as 0. That way
userspace can also know what's the best option.

Maybe in the future we could auto-compute the preferred_bpp from just
taking the first format of the first primary plane, but atm not there.

With the above change:

Reviewed-by: Daniel Vetter <daniel.vetter@...ll.ch>
>  	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