Re: [PATCH] sh: boot: Remove sh5 cache handling

Hi Adrian,

On Mon, Apr 29, 2024 at 9:52 AM John Paul Adrian Glaubitz
<[email protected]> wrote:
> On Mon, 2024-04-29 at 09:49 +0200, Geert Uytterhoeven wrote:
> > On Mon, Apr 29, 2024 at 9:46 AM John Paul Adrian Glaubitz
> > <[email protected]> wrote:
> > > On Wed, 2024-04-24 at 13:54 +0200, Geert Uytterhoeven wrote:
> > > > Commit 37744feebc086908 ("sh: remove sh5 support") in v5.8 forgot to
> > > > remove the sh5 cache handling.
> > > >
> > > > Suggested-by: Yoshinori Sato <[email protected]>
> > > > Signed-off-by: Geert Uytterhoeven <[email protected]>
> >
> > > > --- a/arch/sh/boot/compressed/cache.c
> > > > +++ /dev/null
> > > > @@ -1,13 +0,0 @@
> > > > -// SPDX-License-Identifier: GPL-2.0
> > > > -int cache_control(unsigned int command)
> > > > -{
> > > > -     volatile unsigned int *p = (volatile unsigned int *) 0x80000000;
> > > > -     int i;
> > > > -
> > > > -     for (i = 0; i < (32 * 1024); i += 32) {
> > > > -             (void)*p;
> > > > -             p += (32 / sizeof(int));
> > > > -     }
> > > > -
> > > > -     return 0;
> > > > -}
> >
> > > Interesting, looking at boot/compressed/cache.c, it seems that the whole code
> > > is actually a no-op and does nothing but increasing a pointer. So I agree we
> > > should just delete it.
> >
> > It is not a no-op: it also reads from memory, to load new data in
> > the cache, and evicting the old data.
>
> Yeah, I actually came to this conclusion right after sending my reply. However, the
> command parameter is never used.
>
> Don't have the 32-bit SH CPUs any caches? The code itself is unconditionally executed,
> it seems.

They do. E.g. SH7751 has 8+8 KiB of L1 cache.
But e.g. sh7724 has 32+32KiB L1 cache, and 256 KiB of unified L2 cache.
SH772[34] have l2_cache_init() to enable the L2 cache, so probably they
boot with L2 disabled, and we are fine.

Unfortunately I don't have access to a SH772[34] system.
Sato-san: can you confirm?
Thanks!

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- [email protected]

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds