On Mon, Oct 8, 2018 at 12:21 PM Boris Brezillon
[off-list ref] wrote:

On Mon, 8 Oct 2018 12:06:30 +0200
Arnd Bergmann [off-list ref] wrote:

quoted

On Wed, Oct 3, 2018 at 3:22 PM Boris Brezillon
[off-list ref] wrote:

quoted

Add a driver for Cadence I3C master IP.

Signed-off-by: Boris Brezillon <redacted>
---

quoted

Changes in v7:
- Fix readsl/writesl() usage
- Add a depends on ARM || ARM64 || XTENSA to forbid selection of this
  driver on platforms that are not implementing readsl/writesl

Most architectures include asm-generic/io.h, which contains a generic
implementation of readsl(). Maybe that #ifdef could be extended here?
I remember discussing this with you not so long ago, which led to
commit 0bbf47eab469 ("ia64: use asm-generic/io.h"). Do we have
a list of architectures that don't include asm-generic/io.h? Maybe
the 'depends on' could be for the set of architectures that fail here.

Well, we started patching 2 archs (ia64 and sparc) based on kbuild
robots failure report, and then I received other reports (still from
kbuild robots) long after the initial ones. I can't tell for sure which
archs are not implementing those functions, hence the conservative
approach taken here.

I think it's a fairly safe assumption that architectures which include
asm-generic/io.h will be fine here. If one of them is broken, that
can be fixed individually. Looking at the ones that don't include this
file:

grep -L asm-generic/io.h arch/*/include/asm/io*.h
arch/alpha/include/asm/io.h        # missing readsl
arch/hexagon/include/asm/io.h   # has its own readsl
arch/mips/include/asm/io.h         # missing readsl (but used from ide.h?)
arch/parisc/include/asm/io.h       # missing readsl
arch/powerpc/include/asm/io.h   # has its own readsl
arch/sh/include/asm/io.h             # has its own readsl
arch/sparc/include/asm/io.h        # has its own readsl

Based on this, I would try what happens on mips, and make it depend
on !(ALPHA || PARISC)

Another option is to just use ioread32_rep(), which should be
available everywhere and has almost the same behavior as
readsl(). The only difference is that on architectures like x86
it takes a few extra cycles to look at the address.

        Arnd