Re: [PATCH 00/11] drm/fbdev: Remove DRM's helpers for fbdev I/O

[Sam Ravnborg <sam@ravnborg.org>]

Hi Thomas,

On Fri, May 12, 2023 at 10:41:41AM +0200, Thomas Zimmermann wrote:
> DRM provides a number of wrappers around fbdev cfb_() sys_(), fb_io_()
> and fb_sys_() helpers. The DRM functions don't provide any additional
> functionality for most DRM drivers. So remove them and call the fbdev
> I/O helpers directly.
> 
> The DRM fbdev I/O wrappers were originally added because <linux/fb.h>
> does not protect its content with CONFIG_FB. DRM fbdev emulation did
> not build if the the config option had been disabled. This has been
> fixed. For fbdev-generic and i915, the wrappers added support for damage
> handling. But this is better handled within the two callers, as each
> is special in its damage handling.
> 
> Patches 1 to 8 replace the DRM wrappers in a number of fbdev emulations.
> Patch 9 exports two helpers for damage handling. Patches 10 and 11
> update fbdev-generic and i915 with the help of the exported functions.
> The patches also remove DRM's fbdev I/O helpers, which are now unused.
> 
> DRM's fbdev helpers had to select fbdev I/O helpers for I/O and for
> system memory. Each fbdev emulation now selects the correct helpers
> for itself. Depending on the selected DRM drivers, kernel builds will
> now only contain the necessary fbdev I/O helpers and might be slightly
> smaller in size.

Nice cleanup.

From one of the patches:

> +config DRM_ARMADA_FBDEV_EMULATION
> +     bool
> +     depends on DRM_ARMADA
> +     select FB_CFB_COPYAREA
> +     select FB_CFB_FILLRECT
> +     select FB_CFB_IMAGEBLIT

This seems like a hard to maintain way to select a few helper functions.
Today we have LD_DEAD_CODE_DATA_ELIMINATION for the configs that care
about size - and that should work here as well.

I understand where this comes from and I am not against the
solution, but wanted to point at a more modern approach to deal with the
bloat.

Maybe some of the embbedded folks can tell if LD_DEAD_CODE_DATA_ELIMINATION
can be trusted yet or that is something for the future.

In barebox -ffunction-section (what LD_DEAD_CODE_DATA_ELIMINATION
enables) is used with success - there it really helps when generating
different barebox images where size matters a lot.

	Sam