[PATCH 0/9] T-Head: Allow read access to th.mxstatus CSR

[Inochi Amaoto]

On Wed, Mar 27, 2024 at 11:11:28AM +0100, Christoph Müllner wrote:
> On T-Head C9xx harts, the th.mxstatus CSR provides valuable information
> about the available vendor extensions. As this CSR is only accessible in
> M-mode, we need to provide a mechanism for other modes to access this
> information. This patchset solves this by extending the existing
> platform abstraction such that platforms (or platform overrides)
> can provide a CSR read/write handler.
> 
> A CSR read-handler for th.mxstatus is then added that is utilized by
> the Allwinner D1, the T-Head TH1520, and the Sophgo SG2042.
> Further, a generic mvendorid-based platform override is added that also
> enables the CSR read-handler for th.mxstatus (needed for QEMU).
> 
> The CSR is documented here:
>   https://github.com/T-head-Semi/thead-extension-spec/pull/45
> 
> For QEMU this patch depends on
>   https://lists.gnu.org/archive/html/qemu-devel/2024-03/msg06368.html
> 

Although using something like vendor id to provide basic init code for
platform with the same cpus is a good idea, it may be too hard to
provide common code for the whole vendor. As the cpu evolves, a vendor
may provide something different completely from the previous cpu. This
make provide common code for the entire vendor almost impossible.

There is an another suggestion discussed in the kernel, which suggest
using pseudo extension to provide generic support. I think you want
to check it.
https://lore.kernel.org/all/20240311063018.1886757-1-dqfext@gmail.com/