[PATCH 3/7] riscv: Use NULL as a sentinel value for smp_call_function

[Leo Liang]

Hi, Bin
On Mon, Sep 14, 2020 at 10:07:57AM +0800, Bin Meng wrote:
> Hi Leo,
> 
> On Mon, Sep 14, 2020 at 9:58 AM Leo Liang <ycliang at andestech.com> wrote:
> >
> > On Fri, Sep 11, 2020 at 04:04:13PM +0800, Bin Meng wrote:
> > > On Tue, Sep 8, 2020 at 2:17 AM Sean Anderson <seanga2 at gmail.com> wrote:
> > > >
> > > > Some IPIs may already be pending when U-Boot is started. This could be a
> > > > problem if a secondary hart tries to handle an IPI before the boot hart has
> > > > initialized the IPI device.
> > > >
> > > > This commit uses NULL as a sentinel for secondary harts so they know when
> > > > the IPI is initialized, and it is safe to use the IPI API. The smp addr
> > > > parameter is initialized to NULL by board_init_f_init_reserve. Before this,
> > > > secondary harts wait in wait_for_gd_init.
> > > >
> > > > This imposes a minor restriction because harts may no longer jump to NULL.
> > > > However, given that the RISC-V debug device is likely to be located at
> > > > 0x400, it is unlikely for any RISC-V implementation to have usable ram
> > > > located at 0x0.
> > > >
> > > > Signed-off-by: Sean Anderson <seanga2 at gmail.com>
> > > > ---
> > > >
> > > >  arch/riscv/lib/smp.c | 26 ++++++++++++++++++++++----
> > > >  1 file changed, 22 insertions(+), 4 deletions(-)
> > > >
> > >
> > > Reviewed-by: Bin Meng <bin.meng at windriver.com>
> >
> > Hi Bin,
> >
> > There is a series of follow-up discussion on this patch that you might miss reading.
> >
> > This current patch will cause AE350 to fail booting,
> >
> > so maybe we should wait until Sean's next patch comes up to consider a reviewed-by tag.
> >
> 
> Do we know why AE350 fails to boot with this patch?
>

When booting with bootm command,
boot hart will use smp_call_function(addr, arg0, arg1) to tell other harts to jump to "addr",
and other hart will use handle_ipi() to get the "addr".

The address of bbl+kernel payload when booting with AE350 is at 0x0,
so the "addr" would be 0x0 that other harts have to jump to.

With this patch

+	if (!ipi->addr) {
+		pr_err("smp_function cannot be set to 0x0\n");
+		return -EINVAL;
+	}

+	if (!smp_function)
+		return;

these two code snippets would cause u-boot to hang and thus fail the booting process.

> If some big changes are reworked in newer patches, I believe author
> should remove the tag and re-request the review.
> 

Oh I see! Thanks for the explanation.

> Regards,
> Bin

Best,
Leo