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ce3f7163e4
We have pretty clear evidence that MSIs are getting lost on g4x and
somehow the interrupt logic doesn't seem to recover from that state
even if we try hard to clear the IIR.
Disabling IER around the normal IIR clearing in the irq handler isn't
sufficient to avoid this, so the problem really seems to be further
up the interrupt chain. This should guarantee that there's always
an edge if any IIR bits are set after the interrupt handler is done,
which should normally guarantee that the CPU interrupt is generated.
That approach seems to work perfectly on VLV/CHV, but apparently
not on g4x.
MSI is documented to be broken on 965gm at least. The chipset spec
says MSI is defeatured because interrupts can be delayed or lost,
which fits well with what we're seeing on g4x. Previously we've
already disabled GMBUS interrupts on g4x because somehow GMBUS
manages to raise legacy interrupts even when MSI is enabled.
Since there's such widespread MSI breakahge all over in the pre-gen5
land let's just give up on MSI on these platforms.
Seqno reporting might be negatively affected by this since the legcy
interrupts aren't guaranteed to be ordered with the seqno writes,
whereas MSI interrupts may be? But an occasioanlly missed seqno
seems like a small price to pay for generally working interrupts.
Cc: stable@vger.kernel.org
Cc: Diego Viola <diego.viola@gmail.com>
Tested-by: Diego Viola <diego.viola@gmail.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=101261
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170626203051.28480-1-ville.syrjala@linux.intel.com
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
(cherry picked from commit
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Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. 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.