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