Re: [PATCH v6 08/14] riscv: move boot alternatives to a slightly earlier position

["Heiko Stübner" <heiko@sntech.de>]

Hi Atish,

Am Donnerstag, 10. Februar 2022, 23:42:35 CET schrieb Atish Patra:
> On Wed, Feb 9, 2022 at 4:39 AM Heiko Stuebner <heiko@sntech.de> wrote:
> >
> > Move the application of boot alternatives to soc_early_init().
> > This allows to catch more generic cases of code needing patches
> > than doing it in smp_prepare_boot_cpu() and also makes it actually
> > work if CONFIG_SMP is disabled for whatever reason.
> >
> > The position is chosen mainly as it is before the actual soc early
> > init runs but also already allows accessing the devicetree
> > via fdt_* functions.
> >
> > Signed-off-by: Heiko Stuebner <heiko@sntech.de>
> > ---
> >  arch/riscv/kernel/head.S    | 2 ++
> >  arch/riscv/kernel/smpboot.c | 2 --
> >  2 files changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/riscv/kernel/head.S b/arch/riscv/kernel/head.S
> > index 2363b43312fc..0e1bb97f9749 100644
> > --- a/arch/riscv/kernel/head.S
> > +++ b/arch/riscv/kernel/head.S
> > @@ -10,6 +10,7 @@
> >  #include <asm/thread_info.h>
> >  #include <asm/page.h>
> >  #include <asm/pgtable.h>
> > +#include <asm/alternative.h>
> >  #include <asm/csr.h>
> >  #include <asm/cpu_ops_sbi.h>
> >  #include <asm/hwcap.h>
> > @@ -341,6 +342,7 @@ clear_bss_done:
> >         call kasan_early_init
> >  #endif
> >         /* Start the kernel */
> > +       call apply_boot_alternatives
> 
> Do you really need this early ?
> if non-smp configuration is the only option, Can you do it in
> setup_arch() after riscv_fill_hwcap() is called ?

The issue I see is, we we have the soc_early_init [0] running
directly after this and the one user I see [1] already wants to
ioremap io-memory at this stage.

So judging by the fact that more early-inits will get added
in the future I do guess we should've set up the io-memory
page-type by this point?


Heiko

[0] https://elixir.bootlin.com/linux/latest/source/arch/riscv/kernel/soc.c#L14
[1] https://elixir.bootlin.com/linux/latest/source/drivers/soc/canaan/k210-sysctl.c#L66

> By doing that, we can unify the cpu feature probing and you don't need
> a separate DT parsing just for svpbmt.
> 
> >         call soc_early_init
> >         tail start_kernel
> >
> > diff --git a/arch/riscv/kernel/smpboot.c b/arch/riscv/kernel/smpboot.c
> > index a6d13dca1403..f1e4948a4b52 100644
> > --- a/arch/riscv/kernel/smpboot.c
> > +++ b/arch/riscv/kernel/smpboot.c
> > @@ -32,7 +32,6 @@
> >  #include <asm/sections.h>
> >  #include <asm/sbi.h>
> >  #include <asm/smp.h>
> > -#include <asm/alternative.h>
> >
> >  #include "head.h"
> >
> > @@ -41,7 +40,6 @@ static DECLARE_COMPLETION(cpu_running);
> >  void __init smp_prepare_boot_cpu(void)
> >  {
> >         init_cpu_topology();
> > -       apply_boot_alternatives();
> >  }
> >
> >  void __init smp_prepare_cpus(unsigned int max_cpus)
> > --
> > 2.30.2
> >
> >
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> 
> 
> 
>