Re: [PATCH 2/2] hw/riscv/virt: Introduce strict-dt

[Alistair Francis]

On Sat, Aug 17, 2024 at 2:08 AM Andrew Jones <ajones@ventanamicro.com> wrote:
>
> Older firmwares and OS kernels which use deprecated device tree
> properties or are missing support for new properties may not be
> tolerant of fully compliant device trees. When divergence to the
> bindings specifications is harmless for new firmwares and OS kernels
> which are compliant, then it's probably better to also continue
> supporting the old firmwares and OS kernels by generating
> non-compliant device trees. The '#msi-cells=<0>' property of the
> imsic is one such property. Generating that property doesn't provide
> anything necessary (no '#msi-cells' property or an '#msi-cells'
> property with a value of zero mean the same thing) but it does
> cause PCI devices to fail to find the MSI controller on Linux and,
> for that reason, riscv virt doesn't currently generate it despite
> that putting the DT out of compliance. For users that want a
> compliant DT and know their software supports it, introduce a machine
> property 'strict-dt' to do so. We also drop the one redundant
> property that uses a deprecated name when strict-dt is enabled.
>
> Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
> ---
>  docs/system/riscv/virt.rst | 11 ++++++++++
>  hw/riscv/virt.c            | 43 ++++++++++++++++++++++++++++++--------
>  include/hw/riscv/virt.h    |  1 +
>  3 files changed, 46 insertions(+), 9 deletions(-)
>
> diff --git a/docs/system/riscv/virt.rst b/docs/system/riscv/virt.rst
> index 9a06f95a3444..f08d0a053051 100644
> --- a/docs/system/riscv/virt.rst
> +++ b/docs/system/riscv/virt.rst
> @@ -116,6 +116,17 @@ The following machine-specific options are supported:
>    having AIA IMSIC (i.e. "aia=aplic-imsic" selected). When not specified,
>    the default number of per-HART VS-level AIA IMSIC pages is 0.
>
> +- strict-dt=[on|off]

Hmm... I don't love the idea of having yet another command line option.

Does this really buy us a lot? Eventually we should deprecate the
invalid DT bindings anyway

Alistair