Re: [PATCH 6/7] drm/tilcdc: clean up ifdef hacks around iowrite64

[Arnd Bergmann]

On Mon, Jun 26, 2017 at 6:26 PM, Logan Gunthorpe <logang@xxxxxxxxxxxx> wrote:
> Hi Jyri,
>
> Thanks for the ack. However, I'm reworking this patch set to use the
> include/linux/io-64-nonatomic* headers which will explicitly devolve
> into two 32-bit transfers. It's not clear whether this is appropriate
> for the tilcdc driver as it was never setup to use 32-bit transfers
> (unlike the others I had patched).
>
> If you think it's ok, I can still patch this driver to use the
> non-atomic headers. Otherwise I can leave it out. Please let me know.

You'd have to first figure out whether this device is of the lo-hi
or the hi-lo variant, or doesn't allow the I/O to be split at all.

Note that we could theoretically define ARM to use strd/ldrd
for writeq/readq, but I would expect that to be wrong with many
other devices that can use the existing io-64-nonatomic headers.

The comment in set_scanout() suggests that we actually do rely
on the write64 to be atomic, so we probably don't want to change
this driver.

         Arnd
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