Re: [Qemu-devel] [PATCH v3 2/2] hw/arm/virt-acpi-build: Add SPCR table

[Michael S. Tsirkin]

On Mon, Jun 15, 2015 at 05:59:06PM +0100, Peter Maydell wrote:
> On 15 June 2015 at 17:32, Andrew Jones <address@hidden> wrote:
> > On Mon, Jun 15, 2015 at 06:10:25PM +0200, Michael S. Tsirkin wrote:
> >> On Mon, Jun 15, 2015 at 04:45:58PM +0100, Peter Maydell wrote:
> >> > I'm still confused about when fields in these ACPI structs
> >> > need to be converted to little-endian, and when they don't.
> >> > Is there a rule-of-thumb I can use when I'm looking at patches?
> 
> >> Normally it's all LE unless it's a single byte value.
> >> Did not check this specific table.
> >> We really need to add sparse support to check
> >> endian-ness matches, or re-write it
> >> all using byte_add so there's no duplication of info.
> 
> > Everything used in the table is either a single byte, or I used le32,
> > Well, I didn't bother for the pci_{device,vendor}_id assignments, as
> > they're 0xffff anyway. I can change those two to make them more explicit,
> > if that's preferred.
> 
> Yep, I just looked over the struct definition, so since this
> has been reviewed I'll apply it to target-arm.next.
> 
> You could probably make it easier to review and write
> code that has to do these endianness swaps with something
> like
> 
> #define acpi_struct_assign(FIELD, VAL) \
>   ((FIELD) = \
>   __builtin_choose_expr(sizeof(FIELD) == 1, VAL, \
>   __builtin_choose_expr(sizeof(FIELD) == 2, cpu_to_le16(VAL), \
>   __builtin_choose_expr(sizeof(FIELD) == 4, cpu_to_le32(VAL), \
>   __builtin_choose_expr(sizeof(FIELD) == 8, cpu_to_le64(VAL), \
>   abort))))
> 
> (untested, but based on some code in linux-user/qemu.h).
> 
> Then it's always
> 
>     acpi_struct_assign(spcr->field, value);
> 
> whether the field is 1, 2, 4 or 8 bytes.
> 
> Not my bit of the codebase though, so I'll leave it to the
> ACPI maintainers to decide how much they like magic macros :-)
> 
> thanks
> -- PMM


We don't much. One can use build_append_int_noprefix and just avoid
structs altogether.
We did this for some structures and I'm thinking it's a good direction
generally.

-- 
MST