Re: [PATCH] RISC-V: virt: This is a "sifive,test1" test finisher

[Palmer Dabbelt <palmerdabbelt@google.com>]

On Sun, 10 Nov 2019 13:10:33 PST (-0800), david@gibson.dropbear.id.au wrote:
> On Fri, Nov 08, 2019 at 10:13:16AM -0800, Palmer Dabbelt wrote:
>> On Fri, 08 Nov 2019 10:04:47 PST (-0800), Peter Maydell wrote:
>> > On Fri, 8 Nov 2019 at 17:15, Alistair Francis <alistair23@gmail.com> wrote:
>> > > 
>> > > On Fri, Nov 8, 2019 at 9:05 AM Palmer Dabbelt <palmer@sifive.com> wrote:
>> > > >
>> > > > The test finisher implements the reset command, which means it's a
>> > > > "sifive,test1" device.  This is a backwards compatible change, so it's
>> > > > also a "sifive,test0" device.  I copied the odd idiom for adding a
>> > > > two-string compatible field from the ARM virt board.
>> > > >
>> > > > Fixes: 9a2551ed6f ("riscv: sifive_test: Add reset functionality")
>> > > > Signed-off-by: Palmer Dabbelt <palmer@sifive.com>
>> > > > Signed-off-by: Palmer Dabbelt <palmer@dabbelt.com>
>> > > > ---
>> > > >  hw/riscv/virt.c | 5 ++++-
>> > > >  1 file changed, 4 insertions(+), 1 deletion(-)
>> > > >
>> > > > diff --git a/hw/riscv/virt.c b/hw/riscv/virt.c
>> > > > index 23f340df19..74f2dce81c 100644
>> > > > --- a/hw/riscv/virt.c
>> > > > +++ b/hw/riscv/virt.c
>> > > > @@ -359,7 +359,10 @@ static void create_fdt(RISCVVirtState *s, const struct MemmapEntry *memmap,
>> > > >      nodename = g_strdup_printf("/test@%lx",
>> > > >          (long)memmap[VIRT_TEST].base);
>> > > >      qemu_fdt_add_subnode(fdt, nodename);
>> > > > -    qemu_fdt_setprop_string(fdt, nodename, "compatible", "sifive,test0");
>> > > > +    {
>> > > > +        const char compat[] = "sifive,test1\0sifive,test0";
>> > > 
>> > > Does this really work? Why not use qemu_fdt_setprop_cells()?
>> > > 
>> > > Alistair
>> > > 
>> > > > +        qemu_fdt_setprop(fdt, nodename, "compatible", compat, sizeof(compat));
>> > > > +    }
>> > 
>> > qemu_fdt_setprop_cells() is for "set this property to
>> > contain this list of 32-bit integers" (and it does a byteswap
>> > of each 32-bit value from host to BE). That's not what
>> > you want for a string (or a string list, which is what
>> > we have here).
>> > 
>> > Cc'ing David Gibson who's our device tree expert to see if there's
>> > a nicer way to write this. Oddly, given that it's used in the
>> > ubiquitous 'compatible' prop, the dtc Documentation/manual.txt
>> > doesn't say anything about properties being able to be
>> > 'string lists', only 'strings', '32 bit numbers', 'lists of
>> > 32-bit numbers' and 'byte sequences'. You have to dig through
>> > the header file comments to deduce that a string list is
>> > represented by a string with embedded NULs separating
>> > each list item.
>> 
>> I copied this from hw/arm/virt.c, but messed up.  There they use
>> 
>>        const char compat[] = "arm,armv8-timer\0arm,armv7-timer";
>>        qemu_fdt_setprop(vms->fdt, "/timer", "compatible",
>>                         compat, sizeof(compat));
>
> I'm not sure what you're saying is messed up.  AFAICT, this matches
> the code you have above, and both should be correct.

Sorry, I must have been hallucinating.  For some reason I though I wrote
qemu_fdt_setprop_string(... compat).

I'd like to take this for 4.2 if possible, but I don't think I have a
reviewed-by (I just got my email set up on my Google computer, so it might be
messy for a bit).  I'm happy to submit the cleaner valist version after 4.2, as
per Peter's suggestion.

Alistair: are you OK with this?

>> I'll send a v2, but I'd be happy to add some sort of setprop_stringlist
>> function.  Maybe we just indicate the length with two '\0's?  IIRC that's
>> how other similar-looking data structures are encoded.
>> 
>
> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson