4be9bd10e2
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> Acked-by: Dave Airlie <airlied@gmail.com> Link: https://patchwork.freedesktop.org/patch/msgid/1538136355-15383-1-git-send-email-narmstrong@baylibre.com
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
See Documentation/00-INDEX for a list of what is contained in each file.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.