Re: [RFC PATCH 00/25] Upstream kvx Linux port

[Jules Maselbas <jmaselbas@kalray.eu>]

Hi,

On Wed, Jan 04, 2023 at 04:58:25PM +0100, Arnd Bergmann wrote:
> On Tue, Jan 3, 2023, at 17:43, Yann Sionneau wrote:
> > This patch series adds support for the kv3-1 CPU architecture of the kvx family
> > found in the Coolidge (aka MPPA3-80) SoC of Kalray.
> >
> > This is an RFC, since kvx support is not yet upstreamed into gcc/binutils,
> > therefore this patch series cannot be merged into Linux for now.
> >
> > The goal is to have preliminary reviews and to fix problems early.
> >
> > The Kalray VLIW processor family (kvx) has the following features:
> > * 32/64 bits execution mode
> > * 6-issue VLIW architecture
> > * 64 x 64bits general purpose registers
> > * SIMD instructions
> > * little-endian
> > * deep learning co-processor
> 
> Thanks for posting these, I had been wondering about the
> state of the port. Overall this looks really nice, I can
> see that you and the team have looked at other ports
> and generally made the right decisions.

Thank you and all for the reviews. We are currently going
through every remarks and we are trying to do our best to
send a new patch series with everything addressed.

> I commented on the syscall patch directly, I think it's
> important to stop using the deprecated syscalls as soon
> as possible to avoid having dependencies in too many
> libc binaries. Almost everything else can be changed
> easily as you get closer to upstream inclusion.
> 
> I did not receive most of the other patches as I'm
> not subscribed to all the mainline lists. For future 
> submissions, can you add the linux-arch list to Cc for
> all patches?

We misused get_maintainers.pl, running it on each patch instead
of using it on the whole series. next time every one will be in
copy of every patch in the series and including linux-arch.

> Reading the rest of the series through lore.kernel.org,
> most of the comments I have are for improvements that
> you may find valuable rather than serious mistakes:
> 
> - the {copy_to,copy_from,clear}_user functions are
>   well worth optimizing better than the byte-at-a-time
>   version you have, even just a C version built around
>   your __get_user/__put_user inline asm should help, and
>   could be added to lib/usercopy.c.

right, we are using memcpy for {copy_to,copy_from}_user_page
which has a simple optimized version introduced in
(kvx: Add some library functions).
I wonder if it is possible to do the same for copy_*_user functions.

> - The __raw_{read,write}{b,w,l,q} helpers should
>   normally be defined as inline asm instead of
>   volatile pointer dereferences, I've seen cases where
>   the compiler ends up splitting the access or does
>   other things you may not want on MMIO areas.
>
> - I would recomment implementing HAVE_ARCH_VMAP_STACK
>   as well as IRQ stacks, both of these help to
>   avoid data corruption from stack overflow that you
>   will eventually run into.
> 
> - You use qspinlock as the only available spinlock
>   implementation, but only support running on a
>   single cluster of 16 cores. It may help to use
>   the generic ticket spinlock instead, or leave it
>   as a Kconfig option, in particular since you only
>   have the emulated xchg16() atomic for qspinlock.
> 
> - Your defconfig file enables CONFIG_EMBEDDED, which
>   in turn enables CONFIG_EXPERT. This is probably
>   not what you want, so better turn off both of these.
> 
> - The GENERIC_CALIBRATE_DELAY should not be necessary
>   since you have a get_cycles() based delay loop.
>   Just set loops_per_jiffy to the correct value based
>   on the frequency of the cycle counter, to save
>   a little time during boot and get a more accurate
>   delay loop.
>
Ack !

   Jules