Re: [PATCH v2] drm/fb_helper: Allow leaking fbdev smem_start

[Neil Armstrong <narmstrong@baylibre.com>]

Le 28/09/2018 14:05, Neil Armstrong a écrit :
> Since "drm/fb: Stop leaking physical address", the default behaviour of
> the DRM fbdev emulation is to set the smem_base to 0 and pass the new
> FBINFO_HIDE_SMEM_START flag.
> 
> The main reason is to avoid leaking physical addresse to user-space, and
> it follows a general move over the kernel code to avoid user-space to
> manipulate physical addresses and then use some other mechanisms like
> dma-buf to transfer physical buffer handles over multiple subsystems.
> 
> But, a lot of devices depends on closed sources binaries to enable
> OpenGL hardware acceleration that uses this smem_start value to
> pass physical addresses to out-of-tree modules in order to render
> into these physical adresses. These should use dma-buf buffers allocated
> from the DRM display device instead and stop relying on fbdev overallocation
> to gather DMA memory (some HW vendors delivers GBM and Wayland capable
> binaries, but older unsupported devices won't have these new binaries
> and are doomed until an Open Source solution like Lima finalizes).
> 
> Since these devices heavily depends on this kind of software and because
> the smem_start population was available for years, it's a breakage to
> stop leaking smem_start without any alternative solutions.
> 
> This patch adds a Kconfig depending on the EXPERT config and an unsafe
> kernel module parameter tainting the kernel when enabled.
> 
> A clear comment and Kconfig help text was added to clarify why and when
> this patch should be reverted, but in the meantime it's a necessary
> feature to keep.
> 
> Cc: Dave Airlie <airlied@gmail.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
> Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
> Cc: Noralf Trønnes <noralf@tronnes.org>
> Cc: Maxime Ripard <maxime.ripard@bootlin.com>
> Cc: Eric Anholt <eric@anholt.net>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> Cc: Rob Clark <robdclark@gmail.com>
> Cc: Ben Skeggs <skeggsb@gmail.com>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
> Tested-by: Maxime Ripard <maxime.ripard@bootlin.com>
> Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
> ---
>  drivers/gpu/drm/Kconfig         | 20 ++++++++++++++++++++
>  drivers/gpu/drm/drm_fb_helper.c | 33 +++++++++++++++++++++++++++++++--
>  2 files changed, 51 insertions(+), 2 deletions(-)

Applied to drm-misc-next-fixes with Ack from Dave on irc.

Neil
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