Re: [PATCH v3 1/6] MIPS: Loongson64: Do not write the read only field LPA of CP0_CONFIG3

[Tiezhu Yang]

On 11/04/2020 10:00 AM, Huacai Chen wrote:
> Hi, Tiezhu,
>
> On Tue, Nov 3, 2020 at 3:13 PM Tiezhu Yang <yangtiezhu@xxxxxxxxxxx> wrote:
> > The field LPA of CP0_CONFIG3 register is read only for Loongson64, so the
> > write operations are meaningless, remove them.
> >
> > Signed-off-by: Tiezhu Yang <yangtiezhu@xxxxxxxxxxx>
> > ---
> >
> > v2: No changes
> > v3: No changes
> >
> >   arch/mips/include/asm/mach-loongson64/kernel-entry-init.h | 8 --------
> >   arch/mips/loongson64/numa.c                               | 3 ---
> >   2 files changed, 11 deletions(-)
> >
> > diff --git a/arch/mips/include/asm/mach-loongson64/kernel-entry-init.h b/arch/mips/include/asm/mach-loongson64/kernel-entry-init.h
> > index 87a5bfb..e4d77f4 100644
> > --- a/arch/mips/include/asm/mach-loongson64/kernel-entry-init.h
> > +++ b/arch/mips/include/asm/mach-loongson64/kernel-entry-init.h
> > @@ -19,10 +19,6 @@
> >          .macro  kernel_entry_setup
> >          .set    push
> >          .set    mips64
> > -       /* Set LPA on LOONGSON3 config3 */
> > -       mfc0    t0, CP0_CONFIG3
> > -       or      t0, (0x1 << 7)
> > -       mtc0    t0, CP0_CONFIG3
> Sorry for the late response, I have the same worry as Jiaxun. As you
> know, Loongson's user manuals are not always correct, but the original
> code comes from Loongson are usually better. So, my opinion is "Don't
> change it if it doesn't break anything".

Hi Huacai,

Thanks for your reply, I have confirmed by Loongson user manuals and
hardware designers, CP0_CONFIG3 register is read only.

Without this patch, the related kernel code is meaningless, with
this patch, it can reflect the reality.

Thanks,
Tiezhu

> Huacai
>
> >          /* Set ELPA on LOONGSON3 pagegrain */
> >          mfc0    t0, CP0_PAGEGRAIN
> >          or      t0, (0x1 << 29)
> > @@ -54,10 +50,6 @@
> >          .macro  smp_slave_setup
> >          .set    push
> >          .set    mips64
> > -       /* Set LPA on LOONGSON3 config3 */
> > -       mfc0    t0, CP0_CONFIG3
> > -       or      t0, (0x1 << 7)
> > -       mtc0    t0, CP0_CONFIG3
> >          /* Set ELPA on LOONGSON3 pagegrain */
> >          mfc0    t0, CP0_PAGEGRAIN
> >          or      t0, (0x1 << 29)
> > diff --git a/arch/mips/loongson64/numa.c b/arch/mips/loongson64/numa.c
> > index cf9459f..c7e3cced 100644
> > --- a/arch/mips/loongson64/numa.c
> > +++ b/arch/mips/loongson64/numa.c
> > @@ -40,9 +40,6 @@ static void enable_lpa(void)
> >          unsigned long value;
> >
> >          value = __read_32bit_c0_register($16, 3);
> > -       value |= 0x00000080;
> > -       __write_32bit_c0_register($16, 3, value);
> > -       value = __read_32bit_c0_register($16, 3);
> >          pr_info("CP0_Config3: CP0 16.3 (0x%lx)\n", value);
> >
> >          value = __read_32bit_c0_register($5, 1);
> > --
> > 2.1.0