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Many arm32 board entry points use arm_setup_stack() to set up
the stack from C code. This necessitates using __naked, which
probably has been our most frequent cause of misscompiled C code.
GCC is quite clear that:
Only basic asm statements can safely be included in naked functions
While using extended asm or a mixture of basic asm and C code may
appear to work, they cannot be depended upon to work reliably and
are not supported.
But some boards use it anyway, because it's nice to avoid writing
assembly. Reading generated assembly to spot compiler miscompilation
isn't that nice though, so add some documentation, comments
and compiler diagnostics to hopefully reduce future porting effort.
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210917121152.16033-1-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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Using bthreads throughout means we'll need finer grained locking across
the code base, which is too big a commitment for now. Previous commit
limited bthread_reschedule to only happen in command context, like
how it is for workqueues. Adjust the docs appropriately.
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210622082617.18011-7-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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Clock code sync with Linux got way more straight forward, now that
barebox knows about struct clk_hw. Remove the suggestion to replace
clk_hw with clk when porting.
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Link: https://lore.barebox.org/20210621064646.19094-1-a.fatoum@pengutronix.de
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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Make new porters' life easier by having a central place for porting
advice and add some initial content there.
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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With the new setjmp/longjmp/initjmp support, we have all the
architecture support in place to have suspendable green
threads in barebox. These are expected to replace pollers and
workqueues. For now we still have a differentiation between
the main and secondary threads. The main thread is allowed
I/O access unconditionally. If it's in a delay loop, a secondary
thread running needs to be wary of not entering the same driver
and doing hardware manipulation. We already have slices as
mechanism to guard against this, but they aren't used as widely
as needed.
Preferably, in the end, threads will automatically yield until
they can claim a resource (i.e. lock a mutex). Until we are there,
take the same care when using bthreads as with pollers.
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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With pollers, slices and now workqueues it's time to add some
documentation how these things work and how they all play together.
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
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